18 Feb 2007 11:04:42
TidewayUmpire
Vespoli boats

Can anyone in the UK who has had any experience with Vespoli boats
please assist?

Are they a viable option? e.g. Can damage be repaired easily in the
UK, do any UK manufacturers make riggers for them, whats the delivery
time for spares imported from the US, is it easy to do and are they
[the spares], like for like, any more expensive than other boat
manufacturers?

Thanks for any input



18 Feb 2007 19:49:24
Christopher Anton
Re: Vespoli boats

"TidewayUmpire" <[email protected] > wrote in message
news:[email protected]
> Can anyone in the UK who has had any experience with Vespoli boats
> please assist?
>
> Are they a viable option?

Another important question, do they pass the FISA minimum guidance for the
safe practice of rowing?




18 Feb 2007 11:55:57
Teaplant
Re: Vespoli boats

>Can damage be repaired easily in the UK?

I highly recommend Eric Sims for repairs - Vespoli or otherwise. The
silver lining around the ERB-RIP cloud is that he ought to be much
easier to get to now!

> do any UK manufacturers make riggers for them.

Any/all of them - all riggers should be made 'bespoke' for the boat
after careful measuring and there is usually nothing in particular to
be gained from buying a new boat rigged - saves a few quid perhaps but
do all boatbuilders measure and check every single boat before having
riggers made?
Carl does a very tidy rigger and you can get his details from his
occasional posts to rec.sport.ranting. Just don't mention that the
boat is a poor quality import from a nation with questionable
political situation and a favourable currency exchange rate.

Vespolis themselves always seem quite robust and therefore durable.
However, you don't seem to see many of them in the finals of the World
Champs.... I presume that we are about to see a few more of them about
at club level with the exchange rate as it is at present. Who knows?
Janousek (bullet proof club boats) to go bust next?



19 Feb 2007 05:10:20
Michael Walker
Re: Vespoli boats

On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected] > wrote:
> Can anyone in the UK who has had any experience with Vespoli boats
> please assist?
>
> Are they a viable option? e.g. Can damage be repaired easily in the
> UK, do any UK manufacturers make riggers for them, whats the delivery
> time for spares imported from the US, is it easy to do and are they
> [the spares], like for like, any more expensive than other boat
> manufacturers?
>
> Thanks for any input

One of our Vet eights used one on loan when they went to the Head of
The Charles a couple of years back. They liked it so much they bought
one and imported it. Still cheaper than buying new in the UK from
someone like Aylings or Jano. Do bear in mind - if you go down this
route - that because they're American, fittings etc are NOT metric!



19 Feb 2007 09:25:51
Re: Vespoli boats

My suggestion is that if you are going to buy an American boat try for
other cheaper and more reliable options. If you buy a Vespoli V1 (the
top of the line boat) you spend as much as you spend for a Resolute,
but you end up getting half of the quality. Now that Resolute have a
better customer service and offer some more economical options they
are the better option in the market in my humble opinion.
Neither of the 2 boat builders at the moment are producing a FISA
standards compliant boat. I assume though that at least Resolute will
have no problem to fit their boats with sealed bulkhead.
If you are going for less expensive boats there Hudson and Pocock that
are good alternatives. I think you need to consider the skills of the
crew that is going o use the boat. If your crew is skilled shorter
boats like V1 and Resolute are better options than longer boat like
the M2 and Pocock. Also keep in mind the crew weight: Pocock and
Resolute build a real Midweight boat; V1 are not available yet on that
size so you would get a a cut down HW boat. Let me know if you have
any other questions.

Marco


On Feb 18, 2:04 pm, "TidewayUmpire" <[email protected] > wrote:
> Can anyone in the UK who has had any experience with Vespoli boats
> please assist?
>
> Are they a viable option? e.g. Can damage be repaired easily in the
> UK, do any UK manufacturers make riggers for them, whats the delivery
> time for spares imported from the US, is it easy to do and are they
> [the spares], like for like, any more expensive than other boat
> manufacturers?
>
> Thanks for any input




19 Feb 2007 17:50:13
Christopher Anton
Re: Vespoli boats


<[email protected] > wrote in message
news:[email protected]

> Neither of the 2 boat builders at the moment are producing a FISA
> standards compliant boat.

In that case I wouldn't hesitate to stop it boating at a UK regatta because
it would not comply with the water safety code.




19 Feb 2007 10:25:00
Re: Vespoli boats

You are right Anton but I'm pretty sure that at this moment many boat
builder will consider to fix the problem in order to sell a boat. When
I asked Resolute they told me that they didn't think it would be a
problem. Unfortunately most of the market of the USA boat builder is
internal so they are really not that motivated in making changes that
will increase the weight of the boat (even if only by a little). Here
the race "the-lighter-the-better" is still going on.

M

On Feb 19, 12:50 pm, "Christopher Anton"
<[email protected] > wrote:
> <[email protected]> wrote in message
>
> news:[email protected]
>
> > Neither of the 2 boat builders at the moment are producing a FISA
> > standards compliant boat.
>
> In that case I wouldn't hesitate to stop it boating at a UK regatta because
> it would not comply with the water safety code.




20 Feb 2007 02:02:10
Robin
Re: Vespoli boats

On Feb 19, 5:25 pm, [email protected] wrote:
> My suggestion is that if you are going to buy an American boat try for
> other cheaper and more reliable options. If you buy a Vespoli V1 (the
> top of the line boat) you spend as much as you spend for a Resolute,
> but you end up getting half of the quality. Now that Resolute have a
> better customer service and offer some more economical options they
> are the better option in the market in my humble opinion.
> Neither of the 2 boat builders at the moment are producing a FISA
> standards compliant boat.

I'm not normally a huge fan of Vespolis - but the V1 I coxed in
Seattle last summer had closed bulkheads at every seat AND hatches
between the tracks. I can't comment whether the space enclosed would
'support the crew if swamped' - but it looked at least as enclosed as
a Janousek does. Nice and stiff, and relatively responsive to
steering.

Regarding Pococks and Hudsons. Pococks VIIIs - although good solid
beasties (in particular the side-rigged E8) are not currently built
with enclosed buoyancy. The E8 (based on the late 80s Empacher shape)
sits up nicely for most crews and both the boats I've coxed were a
delight in head and sprint races - but until the underdeck situation
is sorted out, not ideal for the UK.

Hudsons are certainly capable of being built enclosed and were so
during the 2004 (Olympics) season (I think you have to ask them to do
it now) - but I would have some reservations about recommending them
for anything except technically competent crews, because the one I
have experience coxing was very stiff - but also unforgiving and very
twitchy. It either went very fast (in a straight line) - or would
trundle along with one or other side of the boat in the water each
stroke if you have people whose finishes aren't great or just don't
have the power to get it up to running speed. And they don't steer -
6 kilometres of head race wobbling along below running speed and
unable to get easily round even wide corners aren't my idea of fun.
Speaking as a cox, though, despite the problems with steering, they
have a superbly comfortable cox seat area - tonnes of room to stretch
out, and indentations into the inner skin giving space for hips.

Finally - does anyone have any further information as to what the
"alternative" range options are sold by Resolute? They had something
on their website about introducing two new ranges a couple of years
ago, but I was unable to find out any details such as prices,
construction / specification differences etc.



20 Feb 2007 07:29:38
Re: Vespoli boats

On Feb 20, 5:02 am, "Robin" <[email protected] > wrote:
> On Feb 19, 5:25 pm, [email protected] wrote:
>
> > My suggestion is that if you are going to buy an American boat try for
> > other cheaper and more reliable options. If you buy a Vespoli V1 (the
> > top of the line boat) you spend as much as you spend for a Resolute,
> > but you end up getting half of the quality. Now that Resolute have a
> > better customer service and offer some more economical options they
> > are the better option in the market in my humble opinion.
> > Neither of the 2 boat builders at the moment are producing a FISA
> > standards compliant boat.
>
> I'm not normally a huge fan of Vespolis - but the V1 I coxed in
> Seattle last summer had closed bulkheads at every seat AND hatches
> between the tracks. I can't comment whether the space enclosed would
> 'support the crew if swamped' - but it looked at least as enclosed as
> a Janousek does. Nice and stiff, and relatively responsive to
> steering.

You are right on the V1 but they are not built with sealed under-seat
compartment as standard (unless they started this year) and the
stiffness of the boat is really a gamble. at my club they bought 2
last years a HW and a MW (that was actually a cut down HW). The
stiffness of the second wasn't really the same of the HW. Compared to
a Resolute they felt soft. I rowed and coached a MW entry level
Resolute for a couple of summers and I can tell you that was still
stiffer than the latest V1.

>
> Regarding Pococks and Hudsons. Pococks VIIIs - although good solid
> beasties (in particular the side-rigged E8) are not currently built
> with enclosed buoyancy.
>The E8 (based on the late 80s Empacher shape)
> sits up nicely for most crews and both the boats I've coxed were a
> delight in head and sprint races - but until the underdeck situation
> is sorted out, not ideal for the UK.

Actually the "entry level" E8 are nothing more of bath tubs with
riggers. Sturdy and stable but really heavy. Ideal for novices.
The Hypercarbon it's another kind of beast. I really like it and i
think the boat is really stiff and fast in the water and it doesn't
require as much proficiency to be rowed as other shorter shells.
Still they had up to last year any sealed compartment making it really
dangerous. As I mentioned already in this group, I had to fish out of
the Charles crew telling me how they were used to get swamped in
choppy water with their Pocock. The latest episode at the head of the
Charles with the Kids from the Beijing University that sank in the
borrowed Pocock just increase my concerns about the safety of that
boat.
>
> Hudsons are certainly capable of being built enclosed and were so
> during the 2004 (Olympics) season (I think you have to ask them to do
> it now) - but I would have some reservations about recommending them
> for anything except technically competent crews, because the one I
> have experience coxing was very stiff - but also unforgiving and very
> twitchy. It either went very fast (in a straight line) - or would
> trundle along with one or other side of the boat in the water each
> stroke if you have people whose finishes aren't great or just don't
> have the power to get it up to running speed. And they don't steer -
> 6 kilometres of head race wobbling along below running speed and
> unable to get easily round even wide corners aren't my idea of fun.
> Speaking as a cox, though, despite the problems with steering, they
> have a superbly comfortable cox seat area - tonnes of room to stretch
> out, and indentations into the inner skin giving space for hips.
>
> Finally - does anyone have any further information as to what the
> "alternative" range options are sold by Resolute? They had something
> on their website about introducing two new ranges a couple of years
> ago, but I was unable to find out any details such as prices,
> construction / specification differences etc.

I had the opportunity to evaluate the full line of Resolute, but I
don't have a latest prices list.
I think the entry level was good enough for most of the crew up to
national level although I had always preferred to give it to expert
crews since it's a little too responsive for novices. The web sites
now days doesn't show any entry level boat so I am wondering if they
decided to go for just the top of the line version.
Ciao,
Marco



20 Feb 2007 08:37:28
Robin
Re: Vespoli boats


> You are right on the V1 but they are not built with sealed under-seat
> compartment as standard (unless they started this year) and the
> stiffness of the boat is really a gamble. at my club they bought 2
> last years a HW and a MW (that was actually a cut down HW).

The V1 I experienced was either an 06 or an 05. It was definitely
sealed. Re stiffness - bear in mind that my normal VIIIs are 27 year
old english-built Carbocrafts (ie equivalent to the very earliest
Vespolis built on license when they were still called Carbocraft
USA)... so my experience of genuinely stiff boats is relatively
infrequent. I've never been in a Resolute on the water so can't
comment.
>
> > Regarding Pococks and Hudsons. Pococks VIIIs - ...
> >The E8 (based on the late 80s Empacher shape)
....
> Actually the "entry level" E8 are nothing more of bath tubs with
> riggers. Sturdy and stable but really heavy.

I think you're confusing the E8 with either the C8 (also side rigged,
double skin composite but based on the original Pocock Cedar shape
which is a bit longer, heavier, and more stable from memory), or even
their M8 learner shell which genuinely was a bathtub with riggers,
whether built with the earlier wood / composite construction or the
double-skin composite construction later on.

O.K - so the E8 design is quite conservative, being based on an 80s
Empacher shape, and they don't go all out to take them down to FISA
minimum; nor are they built with the Hypercarbon composite. But in my
experience of them they are competitive with all but the top of the
range racing models, and it doesn't take an Olympic crew to make them
fairly fly if you need them to. If they were built enclosed, and
moreover, sectioned at 4-seat, they would work pretty well in UK
conditions for clubs needing a hard-wearing "club"-level VIII, much as
Janousek build good honest boats here in the UK for that kind of
market.

> The Hypercarbon it's another kind of beast. I really like it and i
> think the boat is really stiff and fast ... but .. the latest episode at the head of the
> Charles with the Kids from the Beijing University that sank in the
> borrowed Pocock just increase my concerns about the safety of that
> boat.
>
True. But that goes for any boat which is built and sold unenclosed,
and ultimately, if we want the average safety of the vessels out there
in North America to improve, moves such as those by Mr. Kaschper to
enclose his boats as standard from last year should be applauded,
providing they enclose enough volume to adequately support a seated
crew when swamped. Having experienced a Men's Hwt crew getting
swamped by launch wake in an 06-model midweight Kaschper 4+ with the
enclosed bulkheads - and then being able to row back to the dock to
empty it out - they already seem to be there or thereabouts, or
certainly are a big step in the right direction.


>
>



21 Feb 2007 22:13:56
Lawrence Edwards
Re: Vespoli boats

<[email protected] > wrote in message
news:[email protected]
> Neither of the 2 boat builders at the moment are producing a FISA
> standards compliant boat. I assume though that at least Resolute will
> have no problem to fit their boats with sealed bulkhead.
>
The Resolute 8 I steered at the Head of the Charles a couple of years ago
was fully bouyant, as were all of the other Resolutes I saw. They even had a
section in their brochure explaining that they have tested the boats with
over-weight crews full of water and they are perfectly rowable. I also saw a
US crew in a Resoltue 8 at Women's Henley last year, which was enclosed
under the seats. I've just looked on their website and it is not clear
whether the current designs have enclosed underseat areas, but I would be
surprised if they didn't after having spoken to the owner of the company
about this issue!

They are also very well made, with an excellent finish and very high quality
fittings.

It is the quality of the fittings and finish on the Chinese boats that I
would question. At the World Masters Row Show 2 years ago there were some
Swift boats, the basic hulls and bulkheads looked fine but the riggers,
seats, rails, and nuts and bolts looked as though they had been selected on
the basis of price not quality.

It would be a false economy to save a few grand on a new 8 only to find that
after a moderate amount of use everything started to break.

I apply the same logic to purchasing cars. I've tried many makes over the
years, and settled on Mazdas because they seem to be the only cars which are
both well made and good value for money. NB I have no connetion with either
Mazda or Resolute!

P.S. following the SARA ruling we have retrofitted bulkheads to our Empacher
8. It was not that difficult to do and has not affected the performance
enough to notice. Perhaps at Olympic or World Championship level it might
make a difference, but the quality of the crew is far more important than a
few extra kilos in an 8. It also means you can keep your kit dry....

Lawrence




21 Feb 2007 14:48:22
Gripper
Re: Vespoli boats

On Feb 19, 1:10 pm, "Michael Walker" <[email protected] >
wrote:
> On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected]> wrote:
>
> > Can anyone in the UK who has had any experience with Vespoli boats
> > please assist?
>
> > Are they a viable option? e.g. Can damage be repaired easily in the
> > UK, do any UK manufacturers make riggers for them, whats the delivery
> > time for spares imported from the US, is it easy to do and are they
> > [the spares], like for like, any more expensive than other boat
> > manufacturers?
>
> > Thanks for any input
>
> One of our Vet eights used one on loan when they went to the Head of
> The Charles a couple of years back. They liked it so much they bought
> one and imported it. Still cheaper than buying new in the UK from
> someone like Aylings or Jano. Do bear in mind - if you go down this
> route - that because they're American, fittings etc are NOT metric!

yes, and here it is being overtaken by an 11 year old Sims,
http://clodaghphotos.fpic.co.uk/p38746876.html
Nice boat though!




21 Feb 2007 18:22:21
KC
Rowing it in, was Re: Vespoli boats

Gripper wrote:
> On Feb 19, 1:10 pm, "Michael Walker" <[email protected]>
> wrote:
>> On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected]> wrote:
>>
>>> Can anyone in the UK who has had any experience with Vespoli boats
>>> please assist?
>>> Are they a viable option? e.g. Can damage be repaired easily in the
>>> UK, do any UK manufacturers make riggers for them, whats the delivery
>>> time for spares imported from the US, is it easy to do and are they
>>> [the spares], like for like, any more expensive than other boat
>>> manufacturers?
>>> Thanks for any input
>> One of our Vet eights used one on loan when they went to the Head of
>> The Charles a couple of years back. They liked it so much they bought
>> one and imported it. Still cheaper than buying new in the UK from
>> someone like Aylings or Jano. Do bear in mind - if you go down this
>> route - that because they're American, fittings etc are NOT metric!
>
> yes, and here it is being overtaken by an 11 year old Sims,
> http://clodaghphotos.fpic.co.uk/p38746876.html
> Nice boat though!
>
>

Two seat is doing a great demonstration of what Sully and Paul would
probably call "rowing it in".

-Kieran


21 Feb 2007 15:38:16
Mike Sullivan
Re: Rowing it in, was Re: Vespoli boats


"KC" <[email protected] > wrote in message
news:[email protected]
> Gripper wrote:
>> On Feb 19, 1:10 pm, "Michael Walker" <[email protected]>
>> wrote:
>>> On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected]> wrote:

snip

> Two seat is doing a great demonstration of what Sully and Paul would
> probably call "rowing it in".

"but I have the biggest puddle!"





22 Feb 2007 12:32:29
Re: Rowing it in, was Re: Vespoli boats

On Feb 21, 3:38 pm, "Mike Sullivan" <[email protected] >
wrote:
> "KC" <[email protected]> wrote in message
>
> news:[email protected]
>
> > Gripper wrote:
> >> On Feb 19, 1:10 pm, "Michael Walker" <[email protected]>
> >> wrote:
> >>> On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected]> wrote:
>
> snip
>
> > Two seat is doing a great demonstration of what Sully and Paul would
> > probably call "rowing it in".
>
> "but I have the biggest puddle!"

IOW, size matters? LOL
He'd probably taken his ViErgra, but still missed the timing.

Good lord! Do any of those Ports have two arms?

And here I was thinking it was only Starboards that screw up... [;o)

- Paul Smith



22 Feb 2007 15:46:59
Kieran
Re: Rowing it in, was Re: Vespoli boats

[email protected] wrote:
> On Feb 21, 3:38 pm, "Mike Sullivan" <[email protected]>
> wrote:
>> "KC" <[email protected]> wrote in message
>>
>> news:[email protected]
>>
>>> Gripper wrote:
>>>> On Feb 19, 1:10 pm, "Michael Walker" <[email protected]>
>>>> wrote:
>>>>> On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected]> wrote:
>> snip
>>
>>> Two seat is doing a great demonstration of what Sully and Paul would
>>> probably call "rowing it in".
>> "but I have the biggest puddle!"
>
> IOW, size matters? LOL
> He'd probably taken his ViErgra, but still missed the timing.
>
> Good lord! Do any of those Ports have two arms?
>
> And here I was thinking it was only Starboards that screw up... [;o)
>
> - Paul Smith
>

And here I was thinking you were going to just ignore all my posts! Oh
wait, that was a reply to Mike not me. Hmmm...

-Kieran


22 Feb 2007 13:06:04
Re: Rowing it in, was Re: Vespoli boats

On Feb 22, 12:46 pm, Kieran <[email protected] > wrote:
> [email protected] wrote:
> > On Feb 21, 3:38 pm, "Mike Sullivan" <[email protected]>
> > wrote:
> >> "KC" <[email protected]> wrote in message
>
> >>news:[email protected]du...
>
> >>> Gripper wrote:
> >>>> On Feb 19, 1:10 pm, "Michael Walker" <[email protected]>
> >>>> wrote:
> >>>>> On Feb 18, 7:04 pm, "TidewayUmpire" <[email protected]> wrote:
> >> snip
>
> >>> Two seat is doing a great demonstration of what Sully and Paul would
> >>> probably call "rowing it in".
> >> "but I have the biggest puddle!"
>
> > IOW, size matters? LOL
> > He'd probably taken his ViErgra, but still missed the timing.
>
> > Good lord! Do any of those Ports have two arms?
>
> > And here I was thinking it was only Starboards that screw up... [;o)
>
> > - Paul Smith
>
> And here I was thinking you were going to just ignore all my posts! Oh
> wait, that was a reply to Mike not me. Hmmm...
>
> -Kieran- Hide quoted text -
>
> - Show quoted text -

Are there any in particular that you would like me to give some
attention (respond) to?

You point me at a web resource that I could have sworn you knew I was
very familiar with (Ken Youngs pages), and then another that describes
the blade path of a boat underway (Kleshnev), and then declare that
the path is the same (with presumably the same forces in play)
regardless of the boat being underway or not. Now how can I respond
to something like that? If you don't see the large difference, being
far more expert in the area than my "ignorant" self, I'm having doubts
that I will be able to make much headway attempting an explanation.

The non-sequitor about the pocock integrated backstay "pointing down
at the water", that you came up with, instead of recognizing that it
was bracing against force in the direction of travel, which the vast
majority of force on the pin is being directed, seemed to indicate
that you did not want to seriously consider what I had been trying to
explain. I even offered a small thought experiment, which you did not
respond to, near as I could tell, though maybe I missed your response
in the fray.

- Paul Smith



22 Feb 2007 17:42:12
KC
Lift and blade forces

[email protected] wrote:
> On Feb 22, 12:46 pm, Kieran <[email protected]> wrote:

>> And here I was thinking you were going to just ignore all my posts! Oh
>> wait, that was a reply to Mike not me. Hmmm...
>>
>> -Kieran- Hide quoted text -
>>
>> - Show quoted text -
>
> Are there any in particular that you would like me to give some
> attention (respond) to?
>
> You point me at a web resource that I could have sworn you knew I was
> very familiar with (Ken Youngs pages), and then another that describes
> the blade path of a boat underway (Kleshnev), and then declare that
> the path is the same (with presumably the same forces in play)
> regardless of the boat being underway or not. Now how can I respond
> to something like that? If you don't see the large difference, being
> far more expert in the area than my "ignorant" self, I'm having doubts
> that I will be able to make much headway attempting an explanation.

Paul, that's just a cop-out on your part. At least *I* am trying to
explain this to you. If you don't understand the underlying reasons
behind your claims, then you shouldn't make those claims. If you see a
large difference in blade path due to boat speed, please explain it!
I'm happy to be shown where MY misunderstanding lies. You just have
made no effort at all to support your claim that "the vast majority of
force on the blade at the catch points in the direction of boat travel."
You have stated that claim in not so many words MANY times, and it is
just plain wrong. If you can prove otherwise, please do. If not, quit
claiming it.

> The non-sequitor about the pocock integrated backstay "pointing down
> at the water", that you came up with, instead of recognizing that it
> was bracing against force in the direction of travel, which the vast
> majority of force on the pin is being directed, seemed to indicate
> that you did not want to seriously consider what I had been trying to
> explain. I even offered a small thought experiment, which you did not
> respond to, near as I could tell, though maybe I missed your response
> in the fray.
>
> - Paul Smith

Let's tackle one thing at a time, shall we? Blade path first, the back
stay thing can wait.

(BTW, I had no idea you were "very familiar" with Ken Young's pages.
How was I to know that? Maybe you forgot that while I started on RSR in
1994/5, I took a long break from it for about two or three years, during
which time I think you started posting.)

The path that the blade takes, as illustrated by Young, Kleshnev and
others is determined by the arc of the oar about the pin, and the boat
traveling past the blade. It is not determined by the boat's speed
(small variations in the blade path shape do occur at different speeds,
but on a gross level the shape of the path is roughly the same at all
speeds). If you can explain to me how the path of the blade through the
water is significantly affected by the boat's speed (enough to account
for your claims of where the "majority" of force points), I'll gladly
hear it. One way the path will change: the amount of slip during
midstroke will be much less with lower forces applied to the oar handle
by the rower. So at paddle/light pressure, there is less slip. At full
pressure there is more slip. But the differences in the blade path
shape between full pressure at a 18 and full pressure at a 38, is
negligible despite the large increase in boat speed. Likewise a full
pressure stroke from a stand still will have a VERY similar path to that
of a full pressure stroke in the middle of a race.

If you can accept the above, then the next point is to understand that
the lift that the blade creates is determined by the direction of flow
about the blade. Since the blade path through the water is not affected
by speed, the direction of the force on the blade is the same at various
speeds, for a given oar angle. The lift force on the blade is by
definition perpendicular to the direction of flow about the blade, which
AGAIN is determined by the path of the blade THROUGH the water. The net
resultant force on the blade (lift and drag) is roughly perpendicular to
the blade cord, which for most oars is parallel to the oar shaft. So,
the net resultant force vector acting on the blade during the stroke is
always perpendicular to the oar shaft (or very close to it).

At the catch, given the angle of the oar, much of the force on the blade
points toward the hull. For a 30deg catch angle, 86.6% of the net force
points at the hull, and 50% of the net force points in the desired
propulsive direction. And in case anyone forgot, at 30deg, Pythagoras
gave us the relationship of sqrt(86.6^2 + 50^2) = 100%.

-Kieran


22 Feb 2007 16:23:05
Re: Lift and blade forces

On Feb 22, 2:42 pm, KC <[email protected] > wrote:
> [email protected] wrote:
> > On Feb 22, 12:46 pm, Kieran <[email protected]> wrote:
> >> And here I was thinking you were going to just ignore all my posts! Oh
> >> wait, that was a reply to Mike not me. Hmmm...
>
> >> -Kieran- Hide quoted text -
>
> >> - Show quoted text -
>
> > Are there any in particular that you would like me to give some
> > attention (respond) to?
>
> > You point me at a web resource that I could have sworn you knew I was
> > very familiar with (Ken Youngs pages), and then another that describes
> > the blade path of a boat underway (Kleshnev), and then declare that
> > the path is the same (with presumably the same forces in play)
> > regardless of the boat being underway or not. Now how can I respond
> > to something like that? If you don't see the large difference, being
> > far more expert in the area than my "ignorant" self, I'm having doubts
> > that I will be able to make much headway attempting an explanation.
>
> Paul, that's just a cop-out on your part. At least *I* am trying to
> explain this to you. If you don't understand the underlying reasons
> behind your claims, then you shouldn't make those claims. If you see a
> large difference in blade path due to boat speed, please explain it!

Okay. From a dead stop, take a full power drive and the blade tip
will be extracted from the water futher from the finish line than it
began, this will not happen once the boat is up to racing speed, and
probably not even considerably prior to that. This means the blade is
making a much different path through the water under way than when
stationary and that path varies with the overall speed.

> I'm happy to be shown where MY misunderstanding lies. You just have
> made no effort at all to support your claim that "the vast majority of
> force on the blade at the catch points in the direction of boat travel."

No, I have tried, just to no avail. Plus, you should be able to
explain it much better than I anyhow. (My ignorance and all.)

> You have stated that claim in not so many words MANY times, and it is
> just plain wrong. If you can prove otherwise, please do. If not, quit
> claiming it.

No. And your record of telling me I "have it wrong", "backwards",
whatever, is none to good, IMO.

> > The non-sequitor about the pocock integrated backstay "pointing down
> > at the water", that you came up with, instead of recognizing that it
> > was bracing against force in the direction of travel, which the vast
> > majority of force on the pin is being directed, seemed to indicate
> > that you did not want to seriously consider what I had been trying to
> > explain. I even offered a small thought experiment, which you did not
> > respond to, near as I could tell, though maybe I missed your response
> > in the fray.
>
> > - Paul Smith
>
> Let's tackle one thing at a time, shall we? Blade path first, the back
> stay thing can wait.
>
> (BTW, I had no idea you were "very familiar" with Ken Young's pages.
> How was I to know that? Maybe you forgot that while I started on RSR in
> 1994/5, I took a long break from it for about two or three years, during
> which time I think you started posting.)

Darn, I was sure we'd discussed the Stroke Phase Guide of ErgMonitor,
which was derived directly from Ken Young's work, which I have
mentioned pretty much every time I discuss it. Maybe we didn't
discuss it, but it strains belief that it was not.

> The path that the blade takes, as illustrated by Young, Kleshnev and
> others is determined by the arc of the oar about the pin, and the boat
> traveling past the blade.

Please, make up your mind! That AND is all I was referring to. Now
are you going to claim I said something else and that you are right
and I was wrong? (Let's not go there again, okay?)

> It is not determined by the boat's speed
> (small variations in the blade path shape do occur at different speeds,
> but on a gross level the shape of the path is roughly the same at all
> speeds). If you can explain to me how the path of the blade through the
> water is significantly affected by the boat's speed (enough to account
> for your claims of where the "majority" of force points), I'll gladly
> hear it. One way the path will change: the amount of slip during
> midstroke will be much less with lower forces applied to the oar handle
> by the rower. So at paddle/light pressure, there is less slip. At full
> pressure there is more slip. But the differences in the blade path
> shape between full pressure at a 18 and full pressure at a 38, is
> negligible despite the large increase in boat speed. Likewise a full
> pressure stroke from a stand still will have a VERY similar path to that
> of a full pressure stroke in the middle of a race.

It seems we have a complete failure to communicate going on somewhere,
as that last sentence makes absolutely no sense at all. As discussed
in my reply above.

> If you can accept the above, then the next point is to understand that
> the lift that the blade creates is determined by the direction of flow
> about the blade.

Are you thinking that you are playing a game with me? Of course I
can not accept that, as it's clearly not acceptable. The lift is
result of circulation about the blade and acts in direct opposition to
the resisting forces of drag and inertia, which last time I checked
were parallel with the direction of travel.

BTW - There is almost no lift involved at the blade until the boat is
moving forward, and it's more in proportion to the actual system
speed. i.e. A quick recovery after the first stroke may have the boat
moving fast forward but since the system is still moving quite slow
the lift is still small. One of the reasons that we use abbreviated
strokes off the start, since at that point the blade drag is the
dominate resistive force in use.

> Since the blade path through the water is not affected
> by speed, the direction of the force on the blade is the same at various
> speeds, for a given oar angle. The lift force on the blade is by
> definition perpendicular to the direction of flow about the blade, which
> AGAIN is determined by the path of the blade THROUGH the water. The net
> resultant force on the blade (lift and drag) is roughly perpendicular to
> the blade cord, which for most oars is parallel to the oar shaft. So,
> the net resultant force vector acting on the blade during the stroke is
> always perpendicular to the oar shaft (or very close to it).
>
> At the catch, given the angle of the oar, much of the force on the blade
> points toward the hull. For a 30deg catch angle, 86.6% of the net force
> points at the hull, and 50% of the net force points in the desired
> propulsive direction. And in case anyone forgot, at 30deg, Pythagoras
> gave us the relationship of sqrt(86.6^2 + 50^2) = 100%.
>
> -Kieran- Hide quoted text -
>
> - Show quoted text -

Can't do much with that last bit, since it was relying on the
acceptance of earlier incorrect claims.

- Paul Smith



22 Feb 2007 23:16:46
[email protected]
Re: Lift and blade forces

> At the catch, given the angle of the oar, much of the force on the blade
> points toward the hull. For a 30deg catch angle, 86.6% of the net force
> points at the hull

Very easy to prove. Take the catch with a single blade. Keep the
other one feathered. Just take the first third of the drive in this
configuration. The boat will turn very nicely. Most of the force is
going sideways.

A while ago I initiated a thread about not being able to go straight.
I was told to watch my releases and catches. That solved the
problem. Any differentials during the catch will produce a turning
force. It's a pretty amazing sport. I appreciate more and more of it
as I learn. It requires one to develop a lot of skills.

-Martin



23 Feb 2007 11:59:43
KC
Re: Lift and blade forces

[email protected] wrote:
>> At the catch, given the angle of the oar, much of the force on the blade
>> points toward the hull. For a 30deg catch angle, 86.6% of the net force
>> points at the hull
>
> Very easy to prove. Take the catch with a single blade. Keep the
> other one feathered. Just take the first third of the drive in this
> configuration. The boat will turn very nicely. Most of the force is
> going sideways.
>
> A while ago I initiated a thread about not being able to go straight.
> I was told to watch my releases and catches. That solved the
> problem. Any differentials during the catch will produce a turning
> force. It's a pretty amazing sport. I appreciate more and more of it
> as I learn. It requires one to develop a lot of skills.
>
> -Martin
>


Excellent, Martin. Thank you. That was definitely a simple "why didn't
I think of that?" explanation.

Paul if you're still unconvinced that the "pinch force" exists, I'll
respond to your other post. Meanwhile, Martin's example proves pretty
much everything I was trying to say. Note that this phenomenon happens
regardless of whether the boat is moving or not.

Now, to preempt a likely rebuttal. Given the off axis location of the
point of force application (the pin) even a force applied to only one
pin pointed directly forward would still turn the boat, but not nearly
as much as happens in Martin's example.

-Kieran


23 Feb 2007 09:36:46
[email protected]
Re: Lift and blade forces

> That was definitely a simple "why didn't
> I think of that?" explanation.

Well, if you haven't studied basic Physics (and paid attention)
understanding force vector decomposition could be difficult. I deal
with having to communicate a lot of highly complex technical
information to semi or non-technical people in my business. Because
of this I've become quite adept at coming-up with simple analogies and
simplifications that work.

-Martin



23 Feb 2007 09:40:30
Re: Lift and blade forces

On Feb 23, 8:59 am, KC <[email protected] > wrote:
> [email protected] wrote:
> >> At the catch, given the angle of the oar, much of the force on the blade
> >> points toward the hull. For a 30deg catch angle, 86.6% of the net force
> >> points at the hull
>
> > Very easy to prove. Take the catch with a single blade. Keep the
> > other one feathered. Just take the first third of the drive in this
> > configuration. The boat will turn very nicely. Most of the force is
> > going sideways.
>
> > A while ago I initiated a thread about not being able to go straight.
> > I was told to watch my releases and catches. That solved the
> > problem. Any differentials during the catch will produce a turning
> > force. It's a pretty amazing sport. I appreciate more and more of it
> > as I learn. It requires one to develop a lot of skills.
>
> > -Martin
>
> Excellent, Martin. Thank you. That was definitely a simple "why didn't
> I think of that?" explanation.

What, you've never sculled the bow around when at a stake boat in
cross wind conditions? I find that difficult to believe, but I'll
take your word for it.

> Paul if you're still unconvinced that the "pinch force" exists, I'll
> respond to your other post. Meanwhile, Martin's example proves pretty
> much everything I was trying to say. Note that this phenomenon happens
> regardless of whether the boat is moving or not.

Still completely unconvinced.
But nice crossing of the eyes and dotting the tease. There is a
forest behind those trees.

You keep stating the extreme of "pinch force exists", as if I have
said somewhere that it 'does not exist', which I don't think I have,
but if I have, let's make it clear right now that I am saying that it
is completely insignificant (when the system is at speed), you claim
87% at 30deg catch angle, which may be just fine in the static
situation, but it is not the same, or even close, in the dynamic one.

BTW - If you continue to misrepresent what I have said (aka - making
false claims) and use that to argue against, I'll start asking about
your paper again, since apparently that's equally irritating to you.
For example, I do not ask you when you stopped beating your wife, only
to get the answer that you have not stopped. Which could equally be
interpretted as you are continuing to beat her, or you never started
in the first place. It's all up to the point of view of the person
doing the interpretting. Oops, there is one other answer that would
involve the admission that you had stopped, but I don't think lowly
enough of you to assume that an option.

> Now, to preempt a likely rebuttal. Given the off axis location of the
> point of force application (the pin) even a force applied to only one
> pin pointed directly forward would still turn the boat, but not nearly
> as much as happens in Martin's example.
>
> -Kieran- Hide quoted text -
>
> - Show quoted text -

Perhaps you should dig up Kleshnevs newsletter regarding the different
force profiles required to produce straight tracking in a 2- (I know
you are familiar with that boat.) The turning moment he describes is
between the center of mass of the system and the pins, not our to the
blades.

And still, there are vast differences in what is happening when the
system is underway or not. Sorry that I don't have the required
vocabulary or tools to get this across to you, but in the long run I
don't see it making much difference to either of us. Perhaps if we
ever get a chance to row together it will be easier to demonstrate
many of these things, but I suppose that's quite unlikely too.

- Paul Smith



23 Feb 2007 17:57:37
Carl Douglas
Re: Lift and blade forces

KC wrote:
> [email protected] wrote:
>
>>> At the catch, given the angle of the oar, much of the force on the blade
>>> points toward the hull. For a 30deg catch angle, 86.6% of the net force
>>> points at the hull
>>
>>
>> Very easy to prove. Take the catch with a single blade. Keep the
>> other one feathered. Just take the first third of the drive in this
>> configuration. The boat will turn very nicely. Most of the force is
>> going sideways.
>>
>> A while ago I initiated a thread about not being able to go straight.
>> I was told to watch my releases and catches. That solved the
>> problem. Any differentials during the catch will produce a turning
>> force. It's a pretty amazing sport. I appreciate more and more of it
>> as I learn. It requires one to develop a lot of skills.
>>
>> -Martin
>>
>
>
> Excellent, Martin. Thank you. That was definitely a simple "why didn't
> I think of that?" explanation.
>
> Paul if you're still unconvinced that the "pinch force" exists, I'll
> respond to your other post. Meanwhile, Martin's example proves pretty
> much everything I was trying to say. Note that this phenomenon happens
> regardless of whether the boat is moving or not.
>
> Now, to preempt a likely rebuttal. Given the off axis location of the
> point of force application (the pin) even a force applied to only one
> pin pointed directly forward would still turn the boat, but not nearly
> as much as happens in Martin's example.
>
> -Kieran


The blade path has to be different, depending on whether there is a
standing start or what passes in rowing for steady state. The question
is; "How different?"

At the static start you do not normally reach so far forward because,
there being no forward motion, there can not yet be any component in the
intended direction of the boat to give you a resolved flow along the
blade. However, this being a transient flow situation, you do not get
stall either - that takes some time to become established.

A boat accelerates quite swiftly off the start, reaching ~60% (off my
cuff) of eventual cruise velocity by the end of that first stroke, and
its initial acceleration is greater than that. So you develop
significant boat velocity very soon after the catch & lift will start to
develop in that first part of the stroke. By the finish you will get
the normal development of lift on the blade, following the mid-stroke
stall phase (which may be somewhat extended, especially if you fail to
dig deep enough in the middle to prevent air entrainment, which builds
up rapidly &, because velocity is relatively low, has more time to do so.

Naturally you will can resolve forces acting around a single blade not
only in terms of lift & drag acting perpendicular to & along the blade,
but instead to reveal a side force perpendicular to the boat & a
propulsive force parallel to the boat, at both catch & finish. If you
liken the early & late parts of the blade action to those of a section
of a propeller, then that side force relates directly to the torque
applied to drive the propeller. As with aircraft, rowing has ways to
cancel the effect of the side force, leaving only the axial, propulsive
force - in boats by having a blade on the other side, working in mirror
fashion.

The side force, of itself, does no work because it (normally) moves
nothing. And there is no such thing as pinching the boat at the catch.
What you have is a range of effective loadings & angles of attack on
the blade, which are determined by the prevailing combination of boat
velocity & amount of forward reach, within which range there will be an
optimum for any given boat speed. You get the same situation in
close-hauled sailing (i.e. into the wind), where again the large side
force generated on the sail(s) (if you choose to resolve forces in that
sense) is exactly balanced by an equal but opposite side force acting on
the keel, rudder & immersed hull of the boat. Some sailors try to haul
in the rig too tight and point to close to the wind, some let out too
much mainsheet & sail too far off the wind, but the expert gets it just
right, somewhere between those 2 extremes. And, with sailing as with
rowing, the faster you go the closer the sailor can head into the wind &
the further it makes sense for the rower to reach for the catch.

Was that any help?

Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


23 Feb 2007 13:32:24
KC
Re: Lift and blade forces

[email protected] wrote:
>> That was definitely a simple "why didn't
>> I think of that?" explanation.
>
> Well, if you haven't studied basic Physics (and paid attention)
> understanding force vector decomposition could be difficult. I deal
> with having to communicate a lot of highly complex technical
> information to semi or non-technical people in my business. Because
> of this I've become quite adept at coming-up with simple analogies and
> simplifications that work.
>
> -Martin
>

In contrast, I spend much of my time explaining highly complex technical
information to people who are REQUIRED to understand it (students) so
rather than skip the vector math with an analogy, I must cover it.
Although, often the real-world analogy helps in grasping the tough stuff.

-Kieran


23 Feb 2007 13:33:27
KC
Re: Lift and blade forces

[email protected] wrote:
> On Feb 22, 2:42 pm, KC <[email protected]> wrote:
>> [email protected] wrote:
>>> On Feb 22, 12:46 pm, Kieran <[email protected]> wrote:
>>>> And here I was thinking you were going to just ignore all my posts! Oh
>>>> wait, that was a reply to Mike not me. Hmmm...
>>>> -Kieran- Hide quoted text -
>>>> - Show quoted text -
>>> Are there any in particular that you would like me to give some
>>> attention (respond) to?
>>> You point me at a web resource that I could have sworn you knew I was
>>> very familiar with (Ken Youngs pages), and then another that describes
>>> the blade path of a boat underway (Kleshnev), and then declare that
>>> the path is the same (with presumably the same forces in play)
>>> regardless of the boat being underway or not. Now how can I respond
>>> to something like that? If you don't see the large difference, being
>>> far more expert in the area than my "ignorant" self, I'm having doubts
>>> that I will be able to make much headway attempting an explanation.
>> Paul, that's just a cop-out on your part. At least *I* am trying to
>> explain this to you. If you don't understand the underlying reasons
>> behind your claims, then you shouldn't make those claims. If you see a
>> large difference in blade path due to boat speed, please explain it!
>
> Okay. From a dead stop, take a full power drive and the blade tip
> will be extracted from the water futher from the finish line than it
> began,

The reason that might happen (I've not noticed it but don't dispute that
it might be possible) is due to the extra slip that occurs during the
first stroke. The extra slip is almost all during the mid-stroke. The
first 1/3 of the first stroke has a blade path very similar to any other
stroke, and it is the first 1/3 of the stroke that we're talking about
here. The reason you get extra slip during the first stroke is because
the rowers are able to apply more force on the first stroke (maybe first
few) than other, higher joint velocity strokes. As I said before, the
more force you apply, the more slip you'll get during the mid-stroke.

> this will not happen once the boat is up to racing speed, and

The slip still occurs, just not as much, and the reason why is because
the rowers can't apply as much force as they can when the boat is moving
slower.

> probably not even considerably prior to that. This means the blade is
> making a much different path through the water under way than when
> stationary and that path varies with the overall speed.

Again, the main variation in the path shape is during the mid-stroke,
not during the high-lift portion(s) of the stroke.

>
>> I'm happy to be shown where MY misunderstanding lies. You just have
>> made no effort at all to support your claim that "the vast majority of
>> force on the blade at the catch points in the direction of boat travel."
>
> No, I have tried, just to no avail. Plus, you should be able to
> explain it much better than I anyhow. (My ignorance and all.)

Paul, I can't explain your point of view because I think it is wrong.
If you can't explain your beliefs, then find someone who can. Find and
share ANY web site, paper, book, picture or anything that shows or
explains that the "pinch force" doesn't exist, please. You're the ONLY
person I've come across who makes this claim. All diagrams in every
book or paper or website I've seen show blade force vectors at the catch
that point perpendicular to the oar shaft.

>> You have stated that claim in not so many words MANY times, and it is
>> just plain wrong. If you can prove otherwise, please do. If not, quit
>> claiming it.
>
> No. And your record of telling me I "have it wrong", "backwards",
> whatever, is none to good, IMO.
>
>>> The non-sequitor about the pocock integrated backstay "pointing down
>>> at the water", that you came up with, instead of recognizing that it
>>> was bracing against force in the direction of travel, which the vast
>>> majority of force on the pin is being directed, seemed to indicate
>>> that you did not want to seriously consider what I had been trying to
>>> explain. I even offered a small thought experiment, which you did not
>>> respond to, near as I could tell, though maybe I missed your response
>>> in the fray.
>>> - Paul Smith
>> Let's tackle one thing at a time, shall we? Blade path first, the back
>> stay thing can wait.
>>
>> (BTW, I had no idea you were "very familiar" with Ken Young's pages.
>> How was I to know that? Maybe you forgot that while I started on RSR in
>> 1994/5, I took a long break from it for about two or three years, during
>> which time I think you started posting.)
>
> Darn, I was sure we'd discussed the Stroke Phase Guide of ErgMonitor,

I don't even know what the Stroke Phase Guide is. I don't use EM much,
maybe I'll look at it next time. What's it do, and what's it based on?

> which was derived directly from Ken Young's work, which I have
> mentioned pretty much every time I discuss it. Maybe we didn't
> discuss it, but it strains belief that it was not.
>
>> The path that the blade takes, as illustrated by Young, Kleshnev and
>> others is determined by the arc of the oar about the pin, and the boat
>> traveling past the blade.
>
> Please, make up your mind! That AND is all I was referring to. Now
> are you going to claim I said something else and that you are right
> and I was wrong? (Let's not go there again, okay?)

The boat moves past the blade even on the first stroke. How does that
"AND" in my statement contradict anything I've said? Maybe I've
misunderstood how you think boat velocity affects lift on the blade.
But since you have never explained why or how you think this is so, I
can hardly be blamed for misunderstanding your thoughts. Please share them?

>> It is not determined by the boat's speed
>> (small variations in the blade path shape do occur at different speeds,
>> but on a gross level the shape of the path is roughly the same at all
>> speeds). If you can explain to me how the path of the blade through the
>> water is significantly affected by the boat's speed (enough to account
>> for your claims of where the "majority" of force points), I'll gladly
>> hear it. One way the path will change: the amount of slip during
>> midstroke will be much less with lower forces applied to the oar handle
>> by the rower. So at paddle/light pressure, there is less slip. At full
>> pressure there is more slip. But the differences in the blade path
>> shape between full pressure at a 18 and full pressure at a 38, is
>> negligible despite the large increase in boat speed. Likewise a full
>> pressure stroke from a stand still will have a VERY similar path to that
>> of a full pressure stroke in the middle of a race.
>
> It seems we have a complete failure to communicate going on somewhere,
> as that last sentence makes absolutely no sense at all. As discussed
> in my reply above.

It makes perfect sense. The shape of the blade path is very similar
regardless of boat speed. Yes, there is more slip mid-stroke, but the
general shape of the path is still similar, and in the first 1/3 of the
stroke, it is very similar.

>> If you can accept the above, then the next point is to understand that
>> the lift that the blade creates is determined by the direction of flow
>> about the blade.
>
> Are you thinking that you are playing a game with me? Of course I

Absolutely not.

> can not accept that, as it's clearly not acceptable. The lift is
> result of circulation about the blade and acts in direct opposition to
> the resisting forces of drag and inertia, which last time I checked
> were parallel with the direction of travel.

Where did you check? Where did you get this information that "lift is
result of circulation about the blade and acts in direct opposition to
the resisting forces of drag and inertia,"???? That is a false
statement. Look up the definition of lift, and show me where it says
that it acts in direct opposition to drag and inertia. Lift acts
PERPENDICULAR to drag, and "inertia" is not a force.
http://en.wikipedia.org/wiki/Inertia
So maybe you used the wrong term, what did you mean rather than
"inertia"? The force that acts in direct opposition to the
boat-system's inertia is DRAG. LIFT (the propulsive *component* of it
anyway) acts in the same direction as the boat-system's inertia.
http://en.wikipedia.org/wiki/Lift_%28force%29

>
> BTW - There is almost no lift involved at the blade until the boat is
> moving forward,

That is a chicken-or-egg statement, and not entirely true. Lift on the
blade is produced by the blade slicing through the water (traveling on
it's arc away from the boat), not by the boat moving forward, per se.
The boat must move forward for the blade to travel on its path though,
thus the chicken/egg situation.

> and it's more in proportion to the actual system speed.

Again, I wonder where you got this information. Lift is proportional to
the *square* of velocity of the flow about the lifting body (e.g. the
blade). For a given drive time and drive length (oar angle range), the
velocity of fluid about the blade is going to be virtually the same,
regardless of boat speed.

> i.e. A quick recovery after the first stroke may have the boat
> moving fast forward but since the system is still moving quite slow
> the lift is still small. One of the reasons that we use abbreviated
> strokes off the start, since at that point the blade drag is the
> dominate resistive force in use.

Actually, but using abbreviated strokes, we limit the blade to the
drag-dominant portion of the stroke, not the other way around, as you
suggest. The reason we use abbreviated strokes is to give us
effectively lower gearing while we get the mass of the system up to speed.

>
>> Since the blade path through the water is not affected
>> by speed, the direction of the force on the blade is the same at various
>> speeds, for a given oar angle. The lift force on the blade is by
>> definition perpendicular to the direction of flow about the blade, which
>> AGAIN is determined by the path of the blade THROUGH the water. The net
>> resultant force on the blade (lift and drag) is roughly perpendicular to
>> the blade cord, which for most oars is parallel to the oar shaft. So,
>> the net resultant force vector acting on the blade during the stroke is
>> always perpendicular to the oar shaft (or very close to it).
>>
>> At the catch, given the angle of the oar, much of the force on the blade
>> points toward the hull. For a 30deg catch angle, 86.6% of the net force
>> points at the hull, and 50% of the net force points in the desired
>> propulsive direction. And in case anyone forgot, at 30deg, Pythagoras
>> gave us the relationship of sqrt(86.6^2 + 50^2) = 100%.
>>
>> -Kieran- Hide quoted text -
>>
>> - Show quoted text -
>
> Can't do much with that last bit, since it was relying on the
> acceptance of earlier incorrect claims.

Still waiting for your evidence or references that show that your claims
are correct.

-Kieran


23 Feb 2007 13:54:42
KC
Re: Lift and blade forces

[email protected] wrote:
> On Feb 23, 8:59 am, KC <[email protected]> wrote:
>> [email protected] wrote:
>>>> At the catch, given the angle of the oar, much of the force on the blade
>>>> points toward the hull. For a 30deg catch angle, 86.6% of the net force
>>>> points at the hull
>>> Very easy to prove. Take the catch with a single blade. Keep the
>>> other one feathered. Just take the first third of the drive in this
>>> configuration. The boat will turn very nicely. Most of the force is
>>> going sideways.
>>> A while ago I initiated a thread about not being able to go straight.
>>> I was told to watch my releases and catches. That solved the
>>> problem. Any differentials during the catch will produce a turning
>>> force. It's a pretty amazing sport. I appreciate more and more of it
>>> as I learn. It requires one to develop a lot of skills.
>>> -Martin
>> Excellent, Martin. Thank you. That was definitely a simple "why didn't
>> I think of that?" explanation.
>
> What, you've never sculled the bow around when at a stake boat in
> cross wind conditions? I find that difficult to believe, but I'll
> take your word for it.

What gave you that impression? I just didn't think of the analogy,
that's all. Doesn't mean I haven't done it.

>
>> Paul if you're still unconvinced that the "pinch force" exists, I'll
>> respond to your other post. Meanwhile, Martin's example proves pretty
>> much everything I was trying to say. Note that this phenomenon happens
>> regardless of whether the boat is moving or not.
>
> Still completely unconvinced.
> But nice crossing of the eyes and dotting the tease. There is a
> forest behind those trees.
>
> You keep stating the extreme of "pinch force exists", as if I have
> said somewhere that it 'does not exist', which I don't think I have,
> but if I have, let's make it clear right now that I am saying that it
> is completely insignificant (when the system is at speed), you claim
> 87% at 30deg catch angle, which may be just fine in the static
> situation, but it is not the same, or even close, in the dynamic one.


Fine, forgive me for stating the extreme of "exists". I *ALSO* used
statements like "you think the MAJORITY of force on the blade points
forward." (in the early portions of the drive). Using words like
"majorty" there acknowledges your claim that the side force is "so small
as to be insignificant" (which is STILL false.)

So quit your belly aching. I acknowledge your OFFICIAL, clear stance on
the subject. It's still incorrect.

> BTW - If you continue to misrepresent what I have said (aka - making
> false claims) and use that to argue against, I'll start asking about
> your paper again, since apparently that's equally irritating to you.

I submitted my preliminary work to, it was accepted by, and I'll be
presenting my work at, a regional conference of the American Society of
Biomechanics this spring. Happy?

Oh, and I have not misrepresented what you have said. Your claims about
the pinch/side/lateral forces ARE false claims.

> Perhaps you should dig up Kleshnevs newsletter regarding the different
> force profiles required to produce straight tracking in a 2- (I know
> you are familiar with that boat.) The turning moment he describes is
> between the center of mass of the system and the pins, not our to the
> blades.

Paul, here's some advice: when you find your self in a hole, stop digging.

That newsletter, as well as the portions of _Rowing Faster_ on the same
topic, only contradict your claims. And your statement that the forces
on the pins are some how separate from those at the blades just further
shows your lack of understanding of force mechanics and vectors.

I'm starting to see why you use the Sisyphean animation for your avitar
on the C2 forums: Because anyone who tries to communicate with you is
doomed to never make any progress, and just when they think they've got
somewhere with you, you kick them back down.

-Kieran

> And still, there are vast differences in what is happening when the
> system is underway or not. Sorry that I don't have the required
> vocabulary or tools to get this across to you, but in the long run I
> don't see it making much difference to either of us. Perhaps if we
> ever get a chance to row together it will be easier to demonstrate
> many of these things, but I suppose that's quite unlikely too.
>
> - Paul Smith
>


23 Feb 2007 11:18:12
Re: Lift and blade forces

On Feb 23, 10:54 am, KC <[email protected] > wrote:
> [email protected] wrote:
> > On Feb 23, 8:59 am, KC <[email protected]> wrote:
> >> [email protected] wrote:
> >>>> At the catch, given the angle of the oar, much of the force on the blade
> >>>> points toward the hull. For a 30deg catch angle, 86.6% of the net force
> >>>> points at the hull
> >>> Very easy to prove. Take the catch with a single blade. Keep the
> >>> other one feathered. Just take the first third of the drive in this
> >>> configuration. The boat will turn very nicely. Most of the force is
> >>> going sideways.
> >>> A while ago I initiated a thread about not being able to go straight.
> >>> I was told to watch my releases and catches. That solved the
> >>> problem. Any differentials during the catch will produce a turning
> >>> force. It's a pretty amazing sport. I appreciate more and more of it
> >>> as I learn. It requires one to develop a lot of skills.
> >>> -Martin
> >> Excellent, Martin. Thank you. That was definitely a simple "why didn't
> >> I think of that?" explanation.
>
> > What, you've never sculled the bow around when at a stake boat in
> > cross wind conditions? I find that difficult to believe, but I'll
> > take your word for it.
>
> What gave you that impression? I just didn't think of the analogy,
> that's all. Doesn't mean I haven't done it.
>
>
>
> >> Paul if you're still unconvinced that the "pinch force" exists, I'll
> >> respond to your other post. Meanwhile, Martin's example proves pretty
> >> much everything I was trying to say. Note that this phenomenon happens
> >> regardless of whether the boat is moving or not.
>
> > Still completely unconvinced.
> > But nice crossing of the eyes and dotting the tease. There is a
> > forest behind those trees.
>
> > You keep stating the extreme of "pinch force exists", as if I have
> > said somewhere that it 'does not exist', which I don't think I have,
> > but if I have, let's make it clear right now that I am saying that it
> > is completely insignificant (when the system is at speed), you claim
> > 87% at 30deg catch angle, which may be just fine in the static
> > situation, but it is not the same, or even close, in the dynamic one.
>
> Fine, forgive me for stating the extreme of "exists". I *ALSO* used
> statements like "you think the MAJORITY of force on the blade points
> forward." (in the early portions of the drive). Using words like
> "majorty" there acknowledges your claim that the side force is "so small
> as to be insignificant" (which is STILL false.)

Strike one.

> So quit your belly aching. I acknowledge your OFFICIAL, clear stance on
> the subject. It's still incorrect.

Strike two..

> > BTW - If you continue to misrepresent what I have said (aka - making
> > false claims) and use that to argue against, I'll start asking about
> > your paper again, since apparently that's equally irritating to you.
>
> I submitted my preliminary work to, it was accepted by, and I'll be
> presenting my work at, a regional conference of the American Society of
> Biomechanics this spring. Happy?

No, I turned off interest until I get to see it, as you requested.
All the best however.

> Oh, and I have not misrepresented what you have said. Your claims about
> the pinch/side/lateral forces ARE false claims.

Strike three, yer out!

> > Perhaps you should dig up Kleshnevs newsletter regarding the different
> > force profiles required to produce straight tracking in a 2- (I know
> > you are familiar with that boat.) The turning moment he describes is
> > between the center of mass of the system and the pins, not our to the
> > blades.
>
> Paul, here's some advice: when you find your self in a hole, stop digging.

Thank you for the advice, I'm sure it's well intentioned.

> That newsletter, as well as the portions of _Rowing Faster_ on the same
> topic, only contradict your claims. And your statement that the forces
> on the pins are some how separate from those at the blades just further
> shows your lack of understanding of force mechanics and vectors.

Perhaps, but it's not that complicated is it?

> I'm starting to see why you use the Sisyphean animation for your avitar
> on the C2 forums: Because anyone who tries to communicate with you is
> doomed to never make any progress, and just when they think they've got
> somewhere with you, you kick them back down.
>
> -Kieran

Wow, so I have a lurker/stalker on the C2 forum? Have you argued
anonymously with me there? There are a few with a similar demeaning
tone. Unmask!

It's more like the futile attempt to convince the unconvincible, or
would that be inconvincible?

SissyPuss Must Die! [;o)

Oops, now Carl has weighed in, but I'm at a loss to see where my grave
error has occured. Darn education, I really should have paid more
attention! [:o

- Paul Smith


>
> > And still, there are vast differences in what is happening when the
> > system is underway or not. Sorry that I don't have the required
> > vocabulary or tools to get this across to you, but in the long run I
> > don't see it making much difference to either of us. Perhaps if we
> > ever get a chance to row together it will be easier to demonstrate
> > many of these things, but I suppose that's quite unlikely too.
>
> > - Paul Smith- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -




23 Feb 2007 14:29:44
KC
Re: Lift and blade forces

Carl Douglas wrote:
>
>
> The blade path has to be different, depending on whether there is a
> standing start or what passes in rowing for steady state. The question
> is; "How different?"
>
> At the static start you do not normally reach so far forward because,
> there being no forward motion, there can not yet be any component in the
> intended direction of the boat to give you a resolved flow along the
> blade. However, this being a transient flow situation, you do not get
> stall either - that takes some time to become established.

The confounding part of what you said Carl, is "the intended direction
of the boat". The boat must move for the blade to slide through the
water on it's lift-producing path, but it is not the motion of the boat
that is imperative to producing lift, it is the motion of the blade away
from the hull, through the water, that gives us flow over the blade.
Then of course there must also be some load applied, for a lifting body
in flow sans load produces no lift.

> A boat accelerates quite swiftly off the start, reaching ~60% (off my
> cuff) of eventual cruise velocity by the end of that first stroke, and
> its initial acceleration is greater than that. So you develop
> significant boat velocity very soon after the catch & lift will start to
> develop in that first part of the stroke. By the finish you will get
> the normal development of lift on the blade, following the mid-stroke
> stall phase (which may be somewhat extended, especially if you fail to
> dig deep enough in the middle to prevent air entrainment, which builds
> up rapidly &, because velocity is relatively low, has more time to do so.
>
> Naturally you will can resolve forces acting around a single blade not
> only in terms of lift & drag acting perpendicular to & along the blade,
> but instead to reveal a side force perpendicular to the boat & a
> propulsive force parallel to the boat, at both catch & finish. If you

The lift force is not actually perpendicular to the blade, it is
perpendicular to the free-stream flow. So if the angle of attack at
some point during the stroke is say, 7deg, then the lift vector will be
at an angle of 83 degrees to the blade cord, not 90deg.

However, the total resultant force acting on the blade (resultant of
drag and lift) is very nearly perpendicular to the cord of the blade,
and therefore also to the oar shaft.

> liken the early & late parts of the blade action to those of a section
> of a propeller, then that side force relates directly to the torque
> applied to drive the propeller. As with aircraft, rowing has ways to
> cancel the effect of the side force, leaving only the axial, propulsive
> force - in boats by having a blade on the other side, working in mirror
> fashion.

The side forces cancel out in that they (ideally) do no work. But they
do not disappear insofar as stresses on the boat parts are concerned.
Please correct me if I'm wrong here, Carl.

> The side force, of itself, does no work because it (normally) moves
> nothing. And there is no such thing as pinching the boat at the catch.

Whether you want to call it "pinching" or "two opposing forces that do
no work" the forces do exist, and since the boat parts are not perfectly
incompressible, some lateral compression must occur. If not, please
explain in more detail how this is so.

> What you have is a range of effective loadings & angles of attack on
> the blade, which are determined by the prevailing combination of boat
> velocity & amount of forward reach, within which range there will be an
> optimum for any given boat speed. You get the same situation in
> close-hauled sailing (i.e. into the wind), where again the large side
> force generated on the sail(s) (if you choose to resolve forces in that
> sense) is exactly balanced by an equal but opposite side force acting on
> the keel, rudder & immersed hull of the boat. Some sailors try to haul

I think you mean that the moments cancel out, so the boat doesn't pitch
over, but the forces are not necessarily equal and opposite (unless the
moment arms are equal in length).

> in the rig too tight and point to close to the wind, some let out too
> much mainsheet & sail too far off the wind, but the expert gets it just
> right, somewhere between those 2 extremes. And, with sailing as with
> rowing, the faster you go the closer the sailor can head into the wind &
> the further it makes sense for the rower to reach for the catch.
>
> Was that any help?

Maybe. Keep going, please. I'm not much of a sailor (the scouting
merit badge is about as far as I went) so that analogy is not doing a
lot for me.

Let's focus on the instant before the catch. Pause the frame right
where the squared blade is about to enter the water at the catch. Say
the angle of the shaft to the water flow is 30deg. So we have a blade
about to enter water that is flowing past it at an angle of 30deg. But
*this* angle of the flow to the blade is meaningless, for as soon as
the blade enters the water, it moves along the well described path
that's been linked to and mentioned previously. IF ANYTHING that 30deg
angle of flow to the blade right before the catch would produce NEGATIVE
lift and slow the boat (as is the case with "backing it in"). The flow
toward the blade that produces lift is due ONLY to the blade traveling
away from the boat and through the water, and the resultant "flow"
approaches the blade from the concave (face) side of the blade. This is
why I've been saying that it matters not how fast the flow of water
around the hull is (boat speed) - because that is not the flow that
causes lift forces on the blade. Indeed, the blade virtually never sees
that flow, for as soon as it enters the water, it is moving WITH *that*
flow (negating it) and the only resultant flow about the blade is due to
the blade's travel away from the hull.

-Kieran

-Kieran


23 Feb 2007 14:37:44
KC
Re: Lift and blade forces

[email protected] wrote:
> On Feb 23, 10:54 am, KC <[email protected]> wrote:

> Thank you for the advice, I'm sure it's well intentioned.

Very much so, and you're welcome.

>> That newsletter, as well as the portions of _Rowing Faster_ on the same
>> topic, only contradict your claims. And your statement that the forces
>> on the pins are some how separate from those at the blades just further
>> shows your lack of understanding of force mechanics and vectors.
>
> Perhaps, but it's not that complicated is it?

I don't think so.

>> I'm starting to see why you use the Sisyphean animation for your avitar
>> on the C2 forums: Because anyone who tries to communicate with you is
>> doomed to never make any progress, and just when they think they've got
>> somewhere with you, you kick them back down.
>>
>> -Kieran
>
> Wow, so I have a lurker/stalker on the C2 forum? Have you argued
> anonymously with me there? There are a few with a similar demeaning
> tone. Unmask!

Nope. If I've ever posted there (I have but it's been VERY seldom) it
was under my own name.

> It's more like the futile attempt to convince the unconvincible, or
> would that be inconvincible?

My point exactly... but YOU are the "unconvincible"[sic] ;^)

-Kieran


23 Feb 2007 19:47:47
Carl Douglas
Re: Lift and blade forces

[email protected] wrote:

>
> Oops, now Carl has weighed in, but I'm at a loss to see where my grave
> error has occured. Darn education, I really should have paid more
> attention! [:o
>

Paul - I was criticising no one, nor arguing any point.

On the contrary. By shining another light (I hope) on one of the
issues, I sought to facilitate discussions between you & Kieran.

It's not about any one person being right, but about teamwork -
collectively arriving at the right (or best available) answer & everyone
feeling a glow of satisfaction over the achievement, as when a crew wins
a race.

Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


23 Feb 2007 11:58:05
Re: Lift and blade forces

On Feb 23, 11:37 am, KC <[email protected] > wrote:
> [email protected] wrote:
> > On Feb 23, 10:54 am, KC <[email protected]> wrote:
> > Thank you for the advice, I'm sure it's well intentioned.
>
> Very much so, and you're welcome.
>
> >> That newsletter, as well as the portions of _Rowing Faster_ on the same
> >> topic, only contradict your claims. And your statement that the forces
> >> on the pins are some how separate from those at the blades just further
> >> shows your lack of understanding of force mechanics and vectors.
>
> > Perhaps, but it's not that complicated is it?
>
> I don't think so.
>
> >> I'm starting to see why you use the Sisyphean animation for your avitar
> >> on the C2 forums: Because anyone who tries to communicate with you is
> >> doomed to never make any progress, and just when they think they've got
> >> somewhere with you, you kick them back down.
>
> >> -Kieran
>
> > Wow, so I have a lurker/stalker on the C2 forum? Have you argued
> > anonymously with me there? There are a few with a similar demeaning
> > tone. Unmask!
>
> Nope. If I've ever posted there (I have but it's been VERY seldom) it
> was under my own name.
>
> > It's more like the futile attempt to convince the unconvincible, or
> > would that be inconvincible?
>
> My point exactly... but YOU are the "unconvincible"[sic] ;^)
>
> -Kieran

Well then your point was exactly wrong. At least if it relies on ME
being inconvincible, as I clearly am convincible when being convinced
to a correct conclusion. i.e. I was convinced that: Sliding Riggers do
not produce faster times over 2000m race courses by any inherent
benefit contained in the system.

- Paul Smith



23 Feb 2007 15:04:23
KC
Re: Lift and blade forces

[email protected] wrote:
> On Feb 23, 11:37 am, KC <[email protected]> wrote:
>> [email protected] wrote:
>>> On Feb 23, 10:54 am, KC <[email protected]> wrote:
>>> Thank you for the advice, I'm sure it's well intentioned.
>> Very much so, and you're welcome.
>>
>>>> That newsletter, as well as the portions of _Rowing Faster_ on the same
>>>> topic, only contradict your claims. And your statement that the forces
>>>> on the pins are some how separate from those at the blades just further
>>>> shows your lack of understanding of force mechanics and vectors.
>>> Perhaps, but it's not that complicated is it?
>> I don't think so.
>>
>>>> I'm starting to see why you use the Sisyphean animation for your avitar
>>>> on the C2 forums: Because anyone who tries to communicate with you is
>>>> doomed to never make any progress, and just when they think they've got
>>>> somewhere with you, you kick them back down.
>>>> -Kieran
>>> Wow, so I have a lurker/stalker on the C2 forum? Have you argued
>>> anonymously with me there? There are a few with a similar demeaning
>>> tone. Unmask!
>> Nope. If I've ever posted there (I have but it's been VERY seldom) it
>> was under my own name.
>>
>>> It's more like the futile attempt to convince the unconvincible, or
>>> would that be inconvincible?
>> My point exactly... but YOU are the "unconvincible"[sic] ;^)
>>
>> -Kieran
>
> Well then your point was exactly wrong. At least if it relies on ME
> being inconvincible, as I clearly am convincible when being convinced
> to a correct conclusion. i.e. I was convinced that: Sliding Riggers do
> not produce faster times over 2000m race courses by any inherent
> benefit contained in the system.
>
> - Paul Smith
>

Glad to hear it. Maybe this means then that some day, some one will
convince you that the net force on a blade is nearly always
perpendicular to the shaft at virtually all instances during the drive,
since that is a true statement.

-Kieran


23 Feb 2007 15:10:03
KC
Re: Lift and blade forces

KC wrote:
> [email protected] wrote:
>> On Feb 23, 11:37 am, KC <[email protected]> wrote:
>>> [email protected] wrote:
>>>> On Feb 23, 10:54 am, KC <[email protected]> wrote:
>>>> Thank you for the advice, I'm sure it's well intentioned.
>>> Very much so, and you're welcome.
>>>
>>>>> That newsletter, as well as the portions of _Rowing Faster_ on the
>>>>> same
>>>>> topic, only contradict your claims. And your statement that the
>>>>> forces
>>>>> on the pins are some how separate from those at the blades just
>>>>> further
>>>>> shows your lack of understanding of force mechanics and vectors.
>>>> Perhaps, but it's not that complicated is it?
>>> I don't think so.
>>>
>>>>> I'm starting to see why you use the Sisyphean animation for your
>>>>> avitar
>>>>> on the C2 forums: Because anyone who tries to communicate with you is
>>>>> doomed to never make any progress, and just when they think they've
>>>>> got
>>>>> somewhere with you, you kick them back down.
>>>>> -Kieran
>>>> Wow, so I have a lurker/stalker on the C2 forum? Have you argued
>>>> anonymously with me there? There are a few with a similar demeaning
>>>> tone. Unmask!
>>> Nope. If I've ever posted there (I have but it's been VERY seldom) it
>>> was under my own name.
>>>
>>>> It's more like the futile attempt to convince the unconvincible, or
>>>> would that be inconvincible?
>>> My point exactly... but YOU are the "unconvincible"[sic] ;^)
>>>
>>> -Kieran
>>
>> Well then your point was exactly wrong. At least if it relies on ME
>> being inconvincible, as I clearly am convincible when being convinced
>> to a correct conclusion. i.e. I was convinced that: Sliding Riggers do
>> not produce faster times over 2000m race courses by any inherent
>> benefit contained in the system.
>>
>> - Paul Smith
>>
>
> Glad to hear it. Maybe this means then that some day, some one will
> convince you that the net force on a blade is nearly always
> perpendicular to the shaft at virtually all instances during the drive,
> since that is a true statement.
>
> -Kieran

I'd like to also point out the irony in your last claim. "I am ...
convinceable [sic] when being convinced to a correct conclusion."

One can not be "convinced" to a conclusion they see as correct, for if
they see it as correct they need no convincing. So, that *you* see my
claims as incorrect should not affect your ability to be convinced,
unless you truly are "unconvinceable" (to continue to use our new non-word).

-KC


23 Feb 2007 12:18:57
Re: Lift and blade forces

On Feb 23, 11:47 am, Carl Douglas <[email protected] > wrote:
> [email protected] wrote:
>
> > Oops, now Carl has weighed in, but I'm at a loss to see where my grave
> > error has occured. Darn education, I really should have paid more
> > attention! [:o
>
> Paul - I was criticising no one, nor arguing any point.

Completely understood that part, but thank you for confirming my
meager understanding.

> On the contrary. By shining another light (I hope) on one of the
> issues, I sought to facilitate discussions between you & Kieran.

Yes indeed, I recall another instance of the "propeller" analogy,
along with a reference to how a screw works. i think I even posted a
link to a relevant kitchen utensil, since the blade is acting much
like a finite slice of the propeller at any given point throughout the
drive.

> It's not about any one person being right, but about teamwork -
> collectively arriving at the right (or best available) answer & everyone
> feeling a glow of satisfaction over the achievement, as when a crew wins
> a race.

I don't completely dismiss the teamwork aspect, though even within a
team there can be friendly adversarial relationships, it's good for
proper motivation. My University V8 didn't have to "get along"
outside the boat, just inside. Frankly, I feel as if I'd like Kieran
more than a couple of guys from that boat, and would probably get
along with him better if we happen to meet one day.

> Cheers -
> Carl
> --
> Carl Douglas Racing Shells -
> Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
> Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
> Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)

Cheers Coach! I'll work on the teamwork aspect.

- Paul Smith

PS - Seat arrived, installed and in testing now. Fixed studs would
have been considerably better for mounting, and having a bit of a
riser (much like a standard seat, but probably 30mm in width) would
put some needed clearance above the rollers. I'll get some pictures
up on the web for illustrative purposes. So far I have noticed that
bum placement (settling in) is much better than it was on the rather
cushioned stock Erg Seats.



23 Feb 2007 12:38:43
Re: Lift and blade forces

On Feb 23, 12:10 pm, KC <[email protected] > wrote:
> KC wrote:
> > [email protected] wrote:
> >> On Feb 23, 11:37 am, KC <[email protected]> wrote:
> >>> [email protected] wrote:
> >>>> On Feb 23, 10:54 am, KC <[email protected]> wrote:
> >>>> Thank you for the advice, I'm sure it's well intentioned.
> >>> Very much so, and you're welcome.
>
> >>>>> That newsletter, as well as the portions of _Rowing Faster_ on the
> >>>>> same
> >>>>> topic, only contradict your claims. And your statement that the
> >>>>> forces
> >>>>> on the pins are some how separate from those at the blades just
> >>>>> further
> >>>>> shows your lack of understanding of force mechanics and vectors.
> >>>> Perhaps, but it's not that complicated is it?
> >>> I don't think so.
>
> >>>>> I'm starting to see why you use the Sisyphean animation for your
> >>>>> avitar
> >>>>> on the C2 forums: Because anyone who tries to communicate with you=
is
> >>>>> doomed to never make any progress, and just when they think they've
> >>>>> got
> >>>>> somewhere with you, you kick them back down.
> >>>>> -Kieran
> >>>> Wow, so I have a lurker/stalker on the C2 forum? Have you argued
> >>>> anonymously with me there? There are a few with a similar demeaning
> >>>> tone. Unmask!
> >>> Nope. If I've ever posted there (I have but it's been VERY seldom) it
> >>> was under my own name.
>
> >>>> It's more like the futile attempt to convince the unconvincible, or
> >>>> would that be inconvincible?
> >>> My point exactly... but YOU are the "unconvincible"[sic] ;^)
>
> >>> -Kieran
>
> >> Well then your point was exactly wrong. At least if it relies on ME
> >> being inconvincible, as I clearly am convincible when being convinced
> >> to a correct conclusion. i.e. I was convinced that: Sliding Riggers do
> >> not produce faster times over 2000m race courses by any inherent
> >> benefit contained in the system.
>
> >> - Paul Smith
>
> > Glad to hear it. Maybe this means then that some day, some one will
> > convince you that the net force on a blade is nearly always
> > perpendicular to the shaft at virtually all instances during the drive,
> > since that is a true statement.

Oh, so now it's "nearly" is it?

How about this then: "The propulsive force at the Pin is nearly
always in the direction of hull travel, and that force is parallel to
the force acting at the Blade." (Note, this is exactly in line with
what I have been saying all along. Just a new bunch of words strung
together.)

> > -Kieran
>
> I'd like to also point out the irony in your last claim. "I am ...
> convinceable [sic] when being convinced to a correct conclusion."
>
> One can not be "convinced" to a conclusion they see as correct, for if
> they see it as correct they need no convincing. So, that *you* see my
> claims as incorrect should not affect your ability to be convinced,
> unless you truly are "unconvinceable" (to continue to use our new non-wor=
d).
>
> -KC- Hide quoted text -
>
> - Show quoted text -

Why in the heck do I try?

You can't even stick with the word (real word) that I was using.
I bothered to look it up, though one can only wonder why.
inconvincible
Main Entry: in=B7con=B7vinc=B7ible
Pronunciation: "in-k&n-'vin(t)-s&-b&l
Function: adjective
: incapable of being convinced

Though there doesn't seem to be the opposition term, "convincible".
But it communicates the required meaning well enough.

Yes, the irony is thick, but I think you miss it completely. At least
I am convinced so.

Socrates is rolling in his grave as this continues. My confidence in
reaching critical mass is still high, hopefully a sign of my
persistent optimism.

- Paul Smith



23 Feb 2007 20:57:16
Carl Douglas
Re: Lift and blade forces

KC wrote:
> Carl Douglas wrote:
>
>>
>>
>> The blade path has to be different, depending on whether there is a
>> standing start or what passes in rowing for steady state. The
>> question is; "How different?"
>>
>> At the static start you do not normally reach so far forward because,
>> there being no forward motion, there can not yet be any component in
>> the intended direction of the boat to give you a resolved flow along
>> the blade. However, this being a transient flow situation, you do not
>> get stall either - that takes some time to become established.
>
>
> The confounding part of what you said Carl, is "the intended direction
> of the boat". The boat must move for the blade to slide through the
> water on it's lift-producing path, but it is not the motion of the boat
> that is imperative to producing lift, it is the motion of the blade away
> from the hull, through the water, that gives us flow over the blade.
> Then of course there must also be some load applied, for a lifting body
> in flow sans load produces no lift.

You won't get flow _along_ the blade at a modest angle of attack, the
pre-requisite for generating lift on a foil, until you have forward
motion. You can do the triangle if velocities as well as I can.
Fortunately, you get rapidly increasing forward motion from the outset.

>
>> A boat accelerates quite swiftly off the start, reaching ~60% (off my
>> cuff) of eventual cruise velocity by the end of that first stroke, and
>> its initial acceleration is greater than that. So you develop
>> significant boat velocity very soon after the catch & lift will start
>> to develop in that first part of the stroke. By the finish you will
>> get the normal development of lift on the blade, following the
>> mid-stroke stall phase (which may be somewhat extended, especially if
>> you fail to dig deep enough in the middle to prevent air entrainment,
>> which builds up rapidly &, because velocity is relatively low, has
>> more time to do so.
>>
>> Naturally you will can resolve forces acting around a single blade not
>> only in terms of lift & drag acting perpendicular to & along the
>> blade, but instead to reveal a side force perpendicular to the boat &
>> a propulsive force parallel to the boat, at both catch & finish. If you
>
>
> The lift force is not actually perpendicular to the blade, it is
> perpendicular to the free-stream flow. So if the angle of attack at
> some point during the stroke is say, 7deg, then the lift vector will be
> at an angle of 83 degrees to the blade cord, not 90deg.

It is a convention that we talk about lift & drag forces as being
mutually perpendicular, for which I blame the father of Cartesian
coordinates. Lift forces operate perpendicular to every art of the
surface of a foil (can't be any other way in a fluid), & the true lift
vector is the sum of those local lift vectors (including the negative
ones on the pressure face of the foil & any negative ones on the lifting
face). Similarly with drag, which can only operate parallel to the
local surface. But we opt to combine those forces into a single vector
which we then resolve into lift, perpendicular to a chosen axis of the
foil (easily determined for a symmetrical foil) & drag parallel to the
same axis.

>
> However, the total resultant force acting on the blade (resultant of
> drag and lift) is very nearly perpendicular to the cord of the blade,
> and therefore also to the oar shaft.

Sure, provided that lift predominates over drag, but nothing is for nothing.

>
>> liken the early & late parts of the blade action to those of a section
>> of a propeller, then that side force relates directly to the torque
>> applied to drive the propeller. As with aircraft, rowing has ways to
>> cancel the effect of the side force, leaving only the axial,
>> propulsive force - in boats by having a blade on the other side,
>> working in mirror fashion.
>
>
> The side forces cancel out in that they (ideally) do no work. But they
> do not disappear insofar as stresses on the boat parts are concerned.
> Please correct me if I'm wrong here, Carl.

But I've never noticed a boat getting hot, nor do they change
perceptibly in shape through the stroke. In fact, it is hard to measure
stresses in a rigger because they produce relatively small amounts of
elastic deformation. Much easier to strain-gauge an oar.

>
>> The side force, of itself, does no work because it (normally) moves
>> nothing. And there is no such thing as pinching the boat at the catch.
>
>
> Whether you want to call it "pinching" or "two opposing forces that do
> no work" the forces do exist, and since the boat parts are not perfectly
> incompressible, some lateral compression must occur. If not, please
> explain in more detail how this is so.

As above, the movements are insignificant so the losses are similarly
insignificant.

>
>> What you have is a range of effective loadings & angles of attack on
>> the blade, which are determined by the prevailing combination of boat
>> velocity & amount of forward reach, within which range there will be
>> an optimum for any given boat speed. You get the same situation in
>> close-hauled sailing (i.e. into the wind), where again the large side
>> force generated on the sail(s) (if you choose to resolve forces in
>> that sense) is exactly balanced by an equal but opposite side force
>> acting on the keel, rudder & immersed hull of the boat. Some sailors
>> try to haul
>
>
> I think you mean that the moments cancel out, so the boat doesn't pitch
> over, but the forces are not necessarily equal and opposite (unless the
> moment arms are equal in length).

No, they don't. The moments are additive (in opposite directions above
& below the roll axis) so they work together to _increase_ the degree of
heel of the boat. That's why a monohull keel-boat always has a dense
lump of metal attached to the bottom of a keel as far below the surface
as possible to generate a righting moment as the boat heels. And why
advanced monohulls have canting keels, while dinghies & other
light-displacement sailboats have to stick lumps of humanity out as far
as possible to windward of the centreline, sometimes hiking out on
trapezes - all to generate the necesasry righting moment to keep the
airfoil (the sail) as nearly upright as possible.
>
>> in the rig too tight and point to close to the wind, some let out too
>> much mainsheet & sail too far off the wind, but the expert gets it
>> just right, somewhere between those 2 extremes. And, with sailing as
>> with rowing, the faster you go the closer the sailor can head into the
>> wind & the further it makes sense for the rower to reach for the catch.
>>
>> Was that any help?
>
>
> Maybe. Keep going, please. I'm not much of a sailor (the scouting
> merit badge is about as far as I went) so that analogy is not doing a
> lot for me.

OK. Consider a landyacht (so we can forget about keels). If you point
it head to wind all it feels is wind drag & no lift. Yet it has the
potential, with a good rig, of sailing into the wind at a speed over the
ground of up to 10x the actual wind speed.

Now point the craft at 10 deg to the wind. Sheet in the sail at say 5
deg (you can't exactly, because the sail is a flexible thing, but no
matter). Now you will be getting lift from the sail at 5 deg ahead of
abeam, & you can calculate from that the effective propulsive force felt
by the craft as sin(5) x the actual lift force. You may also be able to
compute the total wind drag on rig & the rest of the craft. If this
multiplied by sin(85) does not exceed the propulsive force, you still
won't be sailing.

Now point another 5 degrees off the wind, keeping the sail similarly
trimmed. By doing this you have doubled your lift force, but hardly
altered your drag forces (you're working in the drag bucket part of the
drag vs angle of attack curve, where drag hardly alters with AOA). You
now have twice as much propulsive force along the new heading and
hopefully that now exceeds the drag forces, so you're sailing!.

OK, you ain't sailing on your intended heading (dead into the wind), but
your velocity made good in that direction is cos(80) of you speed over
the ground, which ain't too far off 100%.

Now ease off another 5 deg on your course. Lift is up by 50%, drag is
still quite low but beginning to creep up, so you go faster still
(sailing speed is all about the ratio of lift to drag), but you are now
only getting cos(75) of your actual speed in your intended direction, so
there's a trade-off to be made. At some point you will find you are
failing to make ground quite so fast in your required direction, so have
hit a local optimum. But you can still re-set your rig, and go and find
another local optimum. And somewhere you will find that best
combination of AOA/rig setting & course.

You can replay all those considerations for an oarblade at the catch,
plus a few more relating to the advantages of longer stroke duration.

Then with the landyacht you have also, as the craft accelerates, to
constantly re-trim & adjust course, because the apparent wind is moving
around & coming ever closer to dead ahead the faster you go.

>
> Let's focus on the instant before the catch. Pause the frame right
> where the squared blade is about to enter the water at the catch. Say
> the angle of the shaft to the water flow is 30deg. So we have a blade
> about to enter water that is flowing past it at an angle of 30deg. But
> *this* angle of the flow to the blade is meaningless, for as soon as
> the blade enters the water, it moves along the well described path
> that's been linked to and mentioned previously. IF ANYTHING that 30deg
> angle of flow to the blade right before the catch would produce NEGATIVE
> lift and slow the boat (as is the case with "backing it in"). The flow
> toward the blade that produces lift is due ONLY to the blade traveling
> away from the boat and through the water, and the resultant "flow"
> approaches the blade from the concave (face) side of the blade. This is
> why I've been saying that it matters not how fast the flow of water
> around the hull is (boat speed) - because that is not the flow that
> causes lift forces on the blade. Indeed, the blade virtually never sees
> that flow, for as soon as it enters the water, it is moving WITH *that*
> flow (negating it) and the only resultant flow about the blade is due to
> the blade's travel away from the hull.
>
> -Kieran
>
> -Kieran

That's me lot for tonight!

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


23 Feb 2007 16:07:30
KC
Re: Lift and blade forces

[email protected] wrote:
> On Feb 23, 12:10 pm, KC <[email protected]> wrote:

>>>> Well then your point was exactly wrong. At least if it relies on ME
>>>> being inconvincible, as I clearly am convincible when being convinced
>>>> to a correct conclusion. i.e. I was convinced that: Sliding Riggers do
>>>> not produce faster times over 2000m race courses by any inherent
>>>> benefit contained in the system.
>>>> - Paul Smith
>>> Glad to hear it. Maybe this means then that some day, some one will
>>> convince you that the net force on a blade is nearly always
>>> perpendicular to the shaft at virtually all instances during the drive,
>>> since that is a true statement.
>
> Oh, so now it's "nearly" is it?
>
> How about this then: "The propulsive force at the Pin is nearly
> always in the direction of hull travel, and that force is parallel to
> the force acting at the Blade." (Note, this is exactly in line with
> what I have been saying all along. Just a new bunch of words strung
> together.)

I don't disagree with that at all. The *propulsive* (component of)
force is by definition in the direction of propulsion. It is only one
component of the total force on the blade (and pin). The rest is
perpendicular to the propulsive force. What I *think* you have disputed
with me is that the resultant force (i.e. total, net, sum force) on the
blade is NEARLY perpendicular to the oar shaft at virtually all
instances during the drive. Is that a fair statement? I don't want to
misrepresent your claims.

I would think you could come up with something more profound than "the
propulsive force is in the direction of hull travel."

>>> -Kieran
>> I'd like to also point out the irony in your last claim. "I am ...
>> convinceable [sic] when being convinced to a correct conclusion."
>>
>> One can not be "convinced" to a conclusion they see as correct, for if
>> they see it as correct they need no convincing. So, that *you* see my
>> claims as incorrect should not affect your ability to be convinced,
>> unless you truly are "unconvinceable" (to continue to use our new non-word).
>>
>> -KC- Hide quoted text -
>>
>> - Show quoted text -
>
> Why in the heck do I try?

I hadn't noticed that you had.

> You can't even stick with the word (real word) that I was using.
> I bothered to look it up, though one can only wonder why.
> inconvincible
> Main Entry: in·con·vinc·ible
> Pronunciation: "in-k&n-'vin(t)-s&-b&l
> Function: adjective
> : incapable of being convinced

Congrats on being a better speller than I. I concede and bow to your
spellingbeeness.

> Though there doesn't seem to be the opposition term, "convincible".
> But it communicates the required meaning well enough.
>
> Yes, the irony is thick, but I think you miss it completely. At least
> I am convinced so.
>
> Socrates is rolling in his grave as this continues. My confidence in
> reaching critical mass is still high, hopefully a sign of my
> persistent optimism.

I don't know much about Philosophy. Feel free to flex your BA degree
and fill me in on the reference to Socrates here. Maybe it'll make you
feel even better... TWO areas where you are superior! Keep it up, I
shiver in the presence of your correctly spelled philosophical superiority.

The irony NOW, is that my mother was an English teacher and my father
has a BA in philosophy. :^P

-Kieran


23 Feb 2007 17:50:25
KC
Re: Lift and blade forces

Carl Douglas wrote:
> KC wrote:
>> Carl Douglas wrote:
>>
>>>
>>>
>>> The blade path has to be different, depending on whether there is a
>>> standing start or what passes in rowing for steady state. The
>>> question is; "How different?"
>>>
>>> At the static start you do not normally reach so far forward because,
>>> there being no forward motion, there can not yet be any component in
>>> the intended direction of the boat to give you a resolved flow along
>>> the blade. However, this being a transient flow situation, you do
>>> not get stall either - that takes some time to become established.
>>
>>
>> The confounding part of what you said Carl, is "the intended direction
>> of the boat". The boat must move for the blade to slide through the
>> water on it's lift-producing path, but it is not the motion of the
>> boat that is imperative to producing lift, it is the motion of the
>> blade away from the hull, through the water, that gives us flow over
>> the blade. Then of course there must also be some load applied, for a
>> lifting body in flow sans load produces no lift.
>
> You won't get flow _along_ the blade at a modest angle of attack, the

Okay... but I'd say that a modest AoA occurs *almost* instantaneously
once the oars are pulled upon by the rower.

> pre-requisite for generating lift on a foil, until you have forward
> motion. You can do the triangle if velocities as well as I can.
> Fortunately, you get rapidly increasing forward motion from the outset.


>
>>
>>> A boat accelerates quite swiftly off the start, reaching ~60% (off my
>>> cuff) of eventual cruise velocity by the end of that first stroke,
>>> and its initial acceleration is greater than that. So you develop
>>> significant boat velocity very soon after the catch & lift will start
>>> to develop in that first part of the stroke. By the finish you will
>>> get the normal development of lift on the blade, following the
>>> mid-stroke stall phase (which may be somewhat extended, especially if
>>> you fail to dig deep enough in the middle to prevent air entrainment,
>>> which builds up rapidly &, because velocity is relatively low, has
>>> more time to do so.
>>>
>>> Naturally you will can resolve forces acting around a single blade
>>> not only in terms of lift & drag acting perpendicular to & along the
>>> blade, but instead to reveal a side force perpendicular to the boat &
>>> a propulsive force parallel to the boat, at both catch & finish. If you
>>
>>
>> The lift force is not actually perpendicular to the blade, it is
>> perpendicular to the free-stream flow. So if the angle of attack at
>> some point during the stroke is say, 7deg, then the lift vector will
>> be at an angle of 83 degrees to the blade cord, not 90deg.
>
> It is a convention that we talk about lift & drag forces as being
> mutually perpendicular, for which I blame the father of Cartesian
> coordinates. Lift forces operate perpendicular to every art of the
> surface of a foil (can't be any other way in a fluid), & the true lift
> vector is the sum of those local lift vectors (including the negative
> ones on the pressure face of the foil & any negative ones on the lifting
> face). Similarly with drag, which can only operate parallel to the
> local surface. But we opt to combine those forces into a single vector
> which we then resolve into lift, perpendicular to a chosen axis of the
> foil (easily determined for a symmetrical foil) & drag parallel to the
> same axis.

Hmmm... well, the way I recall it is that "lift" is *defined* as the sum
of the force components that are in the directions perpendicular to the
free stream flow.

>>
>> However, the total resultant force acting on the blade (resultant of
>> drag and lift) is very nearly perpendicular to the cord of the blade,
>> and therefore also to the oar shaft.
>
> Sure, provided that lift predominates over drag, but nothing is for
> nothing.

Well, I was talking about the case of a rowing oar blade in the early
stages of the drive phase of a stroke. But anyway, drag predominates
over lift in the mid-stroke, yet the net force on the blade is still
perpendicular to the cord. AIUI, as lift and drag gradually exchange
dominance throughout the stroke, the net force on the blade remains
perpendicular to the cord. Is this not correct? Most of the graphs of
blade force I've seen show the resultant vector to be nearly
perpendicular to the blade cord at all times during the stroke.

>>
>>> liken the early & late parts of the blade action to those of a
>>> section of a propeller, then that side force relates directly to the
>>> torque applied to drive the propeller. As with aircraft, rowing has
>>> ways to cancel the effect of the side force, leaving only the axial,
>>> propulsive force - in boats by having a blade on the other side,
>>> working in mirror fashion.
>>
>>
>> The side forces cancel out in that they (ideally) do no work. But
>> they do not disappear insofar as stresses on the boat parts are
>> concerned. Please correct me if I'm wrong here, Carl.
>
> But I've never noticed a boat getting hot, nor do they change
> perceptibly in shape through the stroke. In fact, it is hard to measure
> stresses in a rigger because they produce relatively small amounts of
> elastic deformation. Much easier to strain-gauge an oar.

That the boat elements do not deform, nor heat up, says more about the
design of the boat & materials than the significance (or lack thereof)
of the force, does it not? For level flight of an aircraft, the Lift
force does no work. It is perfectly in opposition to the force of
gravity on the aircraft. That Lift does no work does not mean that the
aircraft does not endure the effects of its application.

Your perspective is (respectfully) from that of a boat builder here. I
am not trying to say that a "pinching" force exists to say that boats
should be designed differently. Boats are obviously designed well
enough to withstand it.

However, if the net resultant force on the blade is perpendicular to the
shaft (as you have agreed) then...

Given a catch angle of 30deg,
with an applied handle force of 577.5N
With force applied at 30deg to the oar handle (due to reach of the
rowers arms)
perpendicular force on the oar handle from the rower is then
Fph = 577.5cos(30) = 500N perpendicular to the handle.
given a scull length of 280cm
inboard of 80cm
the force at the blade is then 200N, perpendicular to the shaft.
At 30 deg oar angle, there will be
Fsb = cos(30)*200N = 173.2N directed toward the boat, and
Fdb = sin(30)*200N = 100N directed "forward" (direction of travel)

So, If I'm wrong I really want to know, because I don't see anything
erroneous there. If I've made a mistake somewhere in some assumption,
or calculation I'd like to know exactly what it is, so that I can get it
right for the future. Paul can't seem to point out my errors, so
hopefully someone else can.

To continue that calclulation... With a perpendicular oar force of 500N
at the handle and 200N at the blade, the reaction of those forces at the
pin is 700N with a direction perpendicular to the oar shaft.

That means, at a 30deg oar angle, there is 350N applied to one pin that
is driving the boat forward, and 606.2N applied to that pin pointing in
toward the boat.

I don't consider ~135lb of force at the pin pointed perpendicular to the
long axis of the hull to be insignificant. Maybe it's not enough to
deflect the pin or stress the riggers much, but it's about a coxswain's
worth of force! :-) So, where is(are) my mistake(s)?

(There is also a reaction from the axial component of the rower's
applied force ("pressure against the pin"). But since it has no
reaction against the water, it can't drive the boat and should be
ignored for calculations of boat propulsion, but for calculations of pin
deflection it could be included. It resolves to Frpa = 144.4i + 250j N
where i is positive away from the hull, and j is positive from stern to
bow.)

>>
>>> The side force, of itself, does no work because it (normally) moves
>>> nothing. And there is no such thing as pinching the boat at the catch.
>>
>>
>> Whether you want to call it "pinching" or "two opposing forces that do
>> no work" the forces do exist, and since the boat parts are not
>> perfectly incompressible, some lateral compression must occur. If
>> not, please explain in more detail how this is so.
>
> As above, the movements are insignificant so the losses are similarly
> insignificant.

Well, I'm not really worried about the losses, or deflections. Only
that there is a significant component of the blade force pointed at the
hull, and that for oar angles greater than 45 degrees, this component is
greater than the component of force which drives the boat forward.

Paul has said that the component of force directed at the boat is "so
small as to be insignificant". If my math, and mechanics have failed
me, I'd sure like to know where. Because as far as I can tell, at the
catch, the amount of force pointing toward the hull is greater than the
amount pointing in the direction of travel.

snipping the part on sailboats.... (great though it was).

-Kieran


23 Feb 2007 15:52:08
Re: Vespoli boats

Sorry to contradict you Lawrence, but you must be either mistaken or
have rowed the only 2 resolute with enclosed bulkhead. Resolute are
famous here because if the stroke drop the water-bottle on the bottom
of the boat it always end up getting stock on the bow (we had several
time to do the "water-bottle dance" with the boat over hour head
trying un-stuck them from the bow and we had a 2004).
Last time I spoke with their reps at the 2006 Head of the Charles they
were planning to follow the FISA rules for the next production, but I
have not seen any of the enclosed 8+ yet.
The "testing" are actually coming from real life experience. Brown
many time race in one of the worse body of water (always really choppy
and windy) and their boat usually don't swamp completely.
I think is because the gunnels (I think it's gunwhales or something
like that in the UK right?) of the Resolute trap a big amount of air
under neat creating buoyancy. Although what really matter is the
result it's not quite the same of having a fully buoyant boat.
On the rest I agree with you they are really great boats:
my favorites when initial price is not a problem and my crew know what
it means to catch. 8^)
Ciao,
Marco

On Feb 21, 5:13 pm, "Lawrence Edwards"
<[email protected] > wrote:
> <[email protected]> wrote in message
>
> news:[email protected]> Neither of the 2 boat builders at the moment are producing a FISA
> > standards compliant boat. I assume though that at least Resolute will
> > have no problem to fit their boats with sealed bulkhead.
>
> The Resolute 8 I steered at the Head of the Charles a couple of years ago
> was fully bouyant, as were all of the other Resolutes I saw. They even had a
> section in their brochure explaining that they have tested the boats with
> over-weight crews full of water and they are perfectly rowable. I also saw a
> US crew in a Resoltue 8 at Women's Henley last year, which was enclosed
> under the seats. I've just looked on their website and it is not clear
> whether the current designs have enclosed underseat areas, but I would be
> surprised if they didn't after having spoken to the owner of the company
> about this issue!
>
> They are also very well made, with an excellent finish and very high quality
> fittings.
>
> It is the quality of the fittings and finish on the Chinese boats that I
> would question. At the World Masters Row Show 2 years ago there were some
> Swift boats, the basic hulls and bulkheads looked fine but the riggers,
> seats, rails, and nuts and bolts looked as though they had been selected on
> the basis of price not quality.
>
> It would be a false economy to save a few grand on a new 8 only to find that
> after a moderate amount of use everything started to break.
>
> I apply the same logic to purchasing cars. I've tried many makes over the
> years, and settled on Mazdas because they seem to be the only cars which are
> both well made and good value for money. NB I have no connetion with either
> Mazda or Resolute!
>
> P.S. following the SARA ruling we have retrofitted bulkheads to our Empacher
> 8. It was not that difficult to do and has not affected the performance
> enough to notice. Perhaps at Olympic or World Championship level it might
> make a difference, but the quality of the crew is far more important than a
> few extra kilos in an 8. It also means you can keep your kit dry....
>
> Lawrence




23 Feb 2007 15:52:42
Re: Vespoli boats

Sorry to contradict you Lawrence, but you must be either mistaken or
have rowed the only 2 resolute with enclosed bulkhead. Resolute are
famous here because if the stroke drop the water-bottle on the bottom
of the boat it always end up getting stock on the bow (we had several
time to do the "water-bottle dance" with the boat over hour head
trying un-stuck them from the bow and we had a 2004).
Last time I spoke with their reps at the 2006 Head of the Charles they
were planning to follow the FISA rules for the next production, but I
have not seen any of the enclosed 8+ yet.
The "testing" are actually coming from real life experience. Brown
many time race in one of the worse body of water (always really choppy
and windy) and their boat usually don't swamp completely.
I think is because the gunnels (I think it's gunwhales or something
like that in the UK right?) of the Resolute trap a big amount of air
under neat creating buoyancy. Although what really matter is the
result it's not quite the same of having a fully buoyant boat.
On the rest I agree with you they are really great boats:
my favorites when initial price is not a problem and my crew know what
it means to catch. 8^)
Ciao,
Marco

On Feb 21, 5:13 pm, "Lawrence Edwards"
<[email protected] > wrote:
> <[email protected]> wrote in message
>
> news:[email protected]> Neither of the 2 boat builders at the moment are producing a FISA
> > standards compliant boat. I assume though that at least Resolute will
> > have no problem to fit their boats with sealed bulkhead.
>
> The Resolute 8 I steered at the Head of the Charles a couple of years ago
> was fully bouyant, as were all of the other Resolutes I saw. They even had a
> section in their brochure explaining that they have tested the boats with
> over-weight crews full of water and they are perfectly rowable. I also saw a
> US crew in a Resoltue 8 at Women's Henley last year, which was enclosed
> under the seats. I've just looked on their website and it is not clear
> whether the current designs have enclosed underseat areas, but I would be
> surprised if they didn't after having spoken to the owner of the company
> about this issue!
>
> They are also very well made, with an excellent finish and very high quality
> fittings.
>
> It is the quality of the fittings and finish on the Chinese boats that I
> would question. At the World Masters Row Show 2 years ago there were some
> Swift boats, the basic hulls and bulkheads looked fine but the riggers,
> seats, rails, and nuts and bolts looked as though they had been selected on
> the basis of price not quality.
>
> It would be a false economy to save a few grand on a new 8 only to find that
> after a moderate amount of use everything started to break.
>
> I apply the same logic to purchasing cars. I've tried many makes over the
> years, and settled on Mazdas because they seem to be the only cars which are
> both well made and good value for money. NB I have no connetion with either
> Mazda or Resolute!
>
> P.S. following the SARA ruling we have retrofitted bulkheads to our Empacher
> 8. It was not that difficult to do and has not affected the performance
> enough to notice. Perhaps at Olympic or World Championship level it might
> make a difference, but the quality of the crew is far more important than a
> few extra kilos in an 8. It also means you can keep your kit dry....
>
> Lawrence




23 Feb 2007 17:56:21
[email protected]
Re: Lift and blade forces

OK, I'm confused here. Which I Iike because it forces me to pull
books off the shelf and dive into some of this very interesting
material.

The term "lift" is being used a lot in this thread. I have never
thought of an oar generating propulsive force (at least the bulk of
it) through lift. I just can't see it. I see an oar as generating
propulsive forces purely by drag. To go to one of my
simplifications: Where do you generate lift if you run into the wind
with a 4 x 8 foot sheet of plywood in front of you (and normal to the
wind)? The force you will experience is 100% drag, right?

Isn't this how an oar blade generates force to propel a boat?

Where does lift come into this equation? The kind of lift that
sustains an airplane or propels a sailboat. Most of the work I've
done in the field is in aerodynamics for model airplane airfoils.
Quite a bit of it, in fact. I even built my own wind tunnel to test
airfoils a while back. I may need to develop the right perspecitve to
see what is happening with an oar blade.

I must admit, RSR is starting to peak my interest in hydrodynamics and
boat design. I know myself. I know where this is leading. I have a
garage full of fiberglass, kevlar and carbon fiber. I see myself
building a boat by the end of the year if this trend continues. :-)

-Martin




24 Feb 2007 00:04:31
Jonny
Re: Lift and blade forces

On Feb 24, 9:56 am, "[email protected]" <[email protected] > wrote:
> OK, I'm confused here.

So are most of the rest of us. Welcome to the club
>
> The term "lift" is being used a lot in this thread. I have never
> thought of an oar generating propulsive force (at least the bulk of
> it) through lift. I just can't see it. I see an oar as generating
> propulsive forces purely by drag. To go to one of my
> simplifications: Where do you generate lift if you run into the wind
> with a 4 x 8 foot sheet of plywood in front of you (and normal to the
> wind)? The force you will experience is 100% drag, right?

You only really have 100% drag when the face of the blade is
perpendicular to the direction of travel (ie 90deg from side of boat,
mid-drive).

>
> Isn't this how an oar blade generates force to propel a boat?
>
> Where does lift come into this equation? The kind of lift that
> sustains an airplane or propels a sailboat. Most of the work I've
> done in the field is in aerodynamics for model airplane airfoils.
> Quite a bit of it, in fact. I even built my own wind tunnel to test
> airfoils a while back. I may need to develop the right perspecitve to
> see what is happening with an oar blade.

http://www.concept2.com/us/products/oars/testing/default.asp

Check out the diagrams and explanatory stuff here. They are trying to
promote a particular product here that many people 'poo-poo' but the
pictures are easy to understand. The physics makes sense for aircraft
wings, but the benefit to rowing is not proven. I have heard many
rowers/coaches refer to the product in question as the "Vortex Edge
Protector".

>
> I must admit, RSR is starting to peak my interest in hydrodynamics and
> boat design. I know myself. I know where this is leading. I have a
> garage full of fiberglass, kevlar and carbon fiber. I see myself
> building a boat by the end of the year if this trend continues. :-)
>
I've got the same dream. I have done a traditional timber boat
building short course and made a lapstrake dingy. Even Carl said it
was quite nice (but I didn't send him any close up pictures)!



24 Feb 2007 01:15:21
[email protected]
Re: Lift and blade forces

> http://www.concept2.com/us/products/oars/testing/default.asp

Ah, that's some of the context that may have been missing for me. The
path and motion of the blade are interesting.

Some quick math looking at these pictures tells me that the blade
might be moving at as much as 60 MPH during the first quarter of the
stroke. This is the part of the stroke where it is being proposed
that the tip of the blade is, effectively, the leading edge of a
wing. On a quick first inspection this makes a lot of sense. And 60
MPH is not trivial (in terms of generating lift) due to the density of
water.

This tells me that you should not apply much force to the oar handle
during the first 1/4 of the drive. If your blade is truly a lift-
generating device...well...blade shape...60MPH in water is a big
deal...

I need to think about this a little. Got a few ideas to play with at
the lake tomorrow.

-Martin



24 Feb 2007 09:25:34
Carl
Re: Lift and blade forces

[email protected] wrote:
> OK, I'm confused here. Which I Iike because it forces me to pull
> books off the shelf and dive into some of this very interesting
> material.
>
> The term "lift" is being used a lot in this thread. I have never
> thought of an oar generating propulsive force (at least the bulk of
> it) through lift. I just can't see it. I see an oar as generating
> propulsive forces purely by drag. To go to one of my
> simplifications: Where do you generate lift if you run into the wind
> with a 4 x 8 foot sheet of plywood in front of you (and normal to the
> wind)? The force you will experience is 100% drag, right?

No. It is "lift" which takes off roofs in gales, lifts sheets of ply,
steers boats (even with those silly flat tin rudders, or the big
barn-door jobs we used to have. And in the first & last thirds of the
stroke it is lift which does most to propel the boat.

With the sheet of ply, it is lift which wrenches it out of your grasp,
but drag which blows it down-wind. Lift is greatest in the part closer
to the leading edge so, since you must hold your sheet of ply roughly in
the centre, as soon as the AOA is enough to allow lift generation the
leading edge flips up & she starts to fly. It is your efforts to hold
the ply still which maintain sufficient wind velocity across the sheet,
As the wind gets her, the sheet first tilts leading-edge up, then as
AOA increases the lift increases proportionately until she hoists up out
of your grip. Then the sheet is carried away by the wind until it
reaches something close enough to wind speed that the lift in whatever
attitude it then has as it tumbles in the air is insufficient to defy
gravity. At which point the sheet falls to the ground, which removes
its leeward motion &, if it bounces or cartwheels on impact, may cause
it to lift & fly some more.

>
> Isn't this how an oar blade generates force to propel a boat?
>
> Where does lift come into this equation? The kind of lift that
> sustains an airplane or propels a sailboat. Most of the work I've
> done in the field is in aerodynamics for model airplane airfoils.
> Quite a bit of it, in fact. I even built my own wind tunnel to test
> airfoils a while back. I may need to develop the right perspecitve to
> see what is happening with an oar blade.

Consider the triangle of velocities at the blade near the catch: a
large component parallel to the boat's axis & a small component
perpendicular to the oar's axis generate a resultant flow (as seen by
the blade) which is roughly parallel with the oar's axis. Then apply
load & you get, as ever, matching lift. That would work fine for a flat
blade, but works rather better for one which is curved along its length
as an oarblade is curved.

You don't push water sideways with the blade - the blade cuts tip-first
through the water. You don't drag through a small packet of water - the
blade slices past large volumes of water (until near mid-stroke, where
it stalls & drags (see the triangle of velocities).

>
> I must admit, RSR is starting to peak my interest in hydrodynamics and
> boat design. I know myself. I know where this is leading. I have a
> garage full of fiberglass, kevlar and carbon fiber. I see myself
> building a boat by the end of the year if this trend continues. :-)
>

That way, madness lies ;)

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


24 Feb 2007 09:26:36
Carl
Re: Lift and blade forces

Jonny wrote:
> On Feb 24, 9:56 am, "[email protected]" <[email protected]> wrote:
>
>>OK, I'm confused here.
>
>
> So are most of the rest of us. Welcome to the club
>
>>The term "lift" is being used a lot in this thread. I have never
>>thought of an oar generating propulsive force (at least the bulk of
>>it) through lift. I just can't see it. I see an oar as generating
>>propulsive forces purely by drag. To go to one of my
>>simplifications: Where do you generate lift if you run into the wind
>>with a 4 x 8 foot sheet of plywood in front of you (and normal to the
>>wind)? The force you will experience is 100% drag, right?
>
>
> You only really have 100% drag when the face of the blade is
> perpendicular to the direction of travel (ie 90deg from side of boat,
> mid-drive).
>
>
>>Isn't this how an oar blade generates force to propel a boat?
>>
>>Where does lift come into this equation? The kind of lift that
>>sustains an airplane or propels a sailboat. Most of the work I've
>>done in the field is in aerodynamics for model airplane airfoils.
>>Quite a bit of it, in fact. I even built my own wind tunnel to test
>>airfoils a while back. I may need to develop the right perspecitve to
>>see what is happening with an oar blade.
>
>
> http://www.concept2.com/us/products/oars/testing/default.asp
>
> Check out the diagrams and explanatory stuff here. They are trying to
> promote a particular product here that many people 'poo-poo' but the
> pictures are easy to understand. The physics makes sense for aircraft
> wings, but the benefit to rowing is not proven. I have heard many
> rowers/coaches refer to the product in question as the "Vortex Edge
> Protector".
>
>
>>I must admit, RSR is starting to peak my interest in hydrodynamics and
>>boat design. I know myself. I know where this is leading. I have a
>>garage full of fiberglass, kevlar and carbon fiber. I see myself
>>building a boat by the end of the year if this trend continues. :-)
>>
>
> I've got the same dream. I have done a traditional timber boat
> building short course and made a lapstrake dingy. Even Carl said it
> was quite nice (but I didn't send him any close up pictures)!
>

It was nice, Jonny.

C

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


24 Feb 2007 10:24:59
Carl
Re: Lift and blade forces

[email protected] wrote:
>>http://www.concept2.com/us/products/oars/testing/default.asp
>
>
> Ah, that's some of the context that may have been missing for me. The
> path and motion of the blade are interesting.
>
> Some quick math looking at these pictures tells me that the blade
> might be moving at as much as 60 MPH during the first quarter of the
> stroke. This is the part of the stroke where it is being proposed
> that the tip of the blade is, effectively, the leading edge of a
> wing. On a quick first inspection this makes a lot of sense. And 60
> MPH is not trivial (in terms of generating lift) due to the density of
> water.
>
> This tells me that you should not apply much force to the oar handle
> during the first 1/4 of the drive. If your blade is truly a lift-
> generating device...well...blade shape...60MPH in water is a big
> deal...
>
> I need to think about this a little. Got a few ideas to play with at
> the lake tomorrow.
>
> -Martin
>

Dunno where you get 60mph from, Martin. More like 4 or 5 m/sec, or 9 to
11 mph. But still oodles to provide all the lift you need.

Next, the lift force on a foil is only the same as the force applied to
that foil, with the AOA self adjusting accordingly. There is no free
lift. If you want propulsion, you must apply load. Otherwise you have
a kind of perpetual motion machine, which is a thermodynamically illegal
version of a free lunch.

The virtue of lift is that it makes a seemingly soft & compliant fluid
remarkably hard. Whereas a body supported in a fluid by drag alone will
fall through it, without options, a lifting foil slicing through a fluid
can generate many times more lift than the drag it incurs, & that lift
can be used to move the foil about in the fluid or at least to prevent
if from falling (as with a wing).

Don't expect fluid dynamics to be intuitive!

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


24 Feb 2007 08:34:41
[email protected]
Re: Lift and blade forces

> No. It is "lift" which takes off roofs in gales, lifts sheets of ply,

I'd prefer to call that a pressure differential.

I've heard from those who propose that lift (as in propeller or
aircraft wing lift) is really about how much air mass is being "pushed
down" by the airfoil rather than the pressure differential concept.
In other words, in a way, the goal is to make a good air pump. When
this "pump" moves air in such a way that it generates more upward
force than drag, you have lift and flight.

-Martin



24 Feb 2007 18:48:21
Carl
Re: Lift and blade forces

[email protected] wrote:
>>No. It is "lift" which takes off roofs in gales, lifts sheets of ply,
>
>
> I'd prefer to call that a pressure differential.
>
> I've heard from those who propose that lift (as in propeller or
> aircraft wing lift) is really about how much air mass is being "pushed
> down" by the airfoil rather than the pressure differential concept.
> In other words, in a way, the goal is to make a good air pump. When
> this "pump" moves air in such a way that it generates more upward
> force than drag, you have lift and flight.
>
> -Martin
>

Lift can be described as the pressure differential, over the area of the
foil, acting perpendicular to the fluid flow due to a reduction in the
pressure in the fluid flowing over one surface compared to that flowing
over the other surface). You can generate substantial lift with flat
"foils" but get more lift over wider angles of attack, & less
stall-sensitivity, from cambered foils.

You will get fluid displacement perpendicular to the flow, of course,
but that can be seen as a consequence of the pressure differential which
cause lift, rather than as a cause of lift. And in generating lift the
objective is to move as large a mass of the surrounding fluid as
possible so that, by keeping its vertical velocity small you minimise
the resulting kinetic energy absorption.

So I see what you mean about the air pump analogy, but I don't think it
represents the process too well

Cheers -
Carl

--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: The Boathouse, Timsway, Chertsey Lane, Staines TW18 3JY, UK
Email: [email protected] Tel: +44(0)1784-456344 Fax: -466550
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)


24 Feb 2007 22:12:48
Kieran
Re: Lift and blade forces

KC wrote:
> Carl Douglas wrote:
>> KC wrote:
>>> Carl Douglas wrote:
>>>
>>>>
>>>>
>>>> The blade path has to be different, depending on whether there is a
>>>> standing start or what passes in rowing for steady state. The
>>>> question is; "How different?"
>>>>
>>>> At the static start you do not normally reach so far forward
>>>> because, there being no forward motion, there can not yet be any
>>>> component in the intended direction of the boat to give you a
>>>> resolved flow along the blade. However, this being a transient flow
>>>> situation, you do not get stall either - that takes some time to
>>>> become established.
>>>
>>>
>>> The confounding part of what you said Carl, is "the intended
>>> direction of the boat". The boat must move for the blade to slide
>>> through the water on it's lift-producing path, but it is not the
>>> motion of the boat that is imperative to producing lift, it is the
>>> motion of the blade away from the hull, through the water, that gives
>>> us flow over the blade. Then of course there must also be some load
>>> applied, for a lifting body in flow sans load produces no lift.
>>
>> You won't get flow _along_ the blade at a modest angle of attack, the
>
> Okay... but I'd say that a modest AoA occurs *almost* instantaneously
> once the oars are pulled upon by the rower.
>
>> pre-requisite for generating lift on a foil, until you have forward
>> motion. You can do the triangle if velocities as well as I can.
>> Fortunately, you get rapidly increasing forward motion from the outset.
>
>
>>
>>>
>>>> A boat accelerates quite swiftly off the start, reaching ~60% (off
>>>> my cuff) of eventual cruise velocity by the end of that first
>>>> stroke, and its initial acceleration is greater than that. So you
>>>> develop significant boat velocity very soon after the catch & lift
>>>> will start to develop in that first part of the stroke. By the
>>>> finish you will get the normal development of lift on the blade,
>>>> following the mid-stroke stall phase (which may be somewhat
>>>> extended, especially if you fail to dig deep enough in the middle to
>>>> prevent air entrainment, which builds up rapidly &, because velocity
>>>> is relatively low, has more time to do so.
>>>>
>>>> Naturally you will can resolve forces acting around a single blade
>>>> not only in terms of lift & drag acting perpendicular to & along the
>>>> blade, but instead to reveal a side force perpendicular to the boat
>>>> & a propulsive force parallel to the boat, at both catch & finish.
>>>> If you
>>>
>>>
>>> The lift force is not actually perpendicular to the blade, it is
>>> perpendicular to the free-stream flow. So if the angle of attack at
>>> some point during the stroke is say, 7deg, then the lift vector will
>>> be at an angle of 83 degrees to the blade cord, not 90deg.
>>
>> It is a convention that we talk about lift & drag forces as being
>> mutually perpendicular, for which I blame the father of Cartesian
>> coordinates. Lift forces operate perpendicular to every art of the
>> surface of a foil (can't be any other way in a fluid), & the true lift
>> vector is the sum of those local lift vectors (including the negative
>> ones on the pressure face of the foil & any negative ones on the
>> lifting face). Similarly with drag, which can only operate parallel
>> to the local surface. But we opt to combine those forces into a
>> single vector which we then resolve into lift, perpendicular to a
>> chosen axis of the foil (easily determined for a symmetrical foil) &
>> drag parallel to the same axis.
>
> Hmmm... well, the way I recall it is that "lift" is *defined* as the sum
> of the force components that are in the directions perpendicular to the
> free stream flow.
>
>>>
>>> However, the total resultant force acting on the blade (resultant of
>>> drag and lift) is very nearly perpendicular to the cord of the blade,
>>> and therefore also to the oar shaft.
>>
>> Sure, provided that lift predominates over drag, but nothing is for
>> nothing.
>
> Well, I was talking about the case of a rowing oar blade in the early
> stages of the drive phase of a stroke. But anyway, drag predominates
> over lift in the mid-stroke, yet the net force on the blade is still
> perpendicular to the cord. AIUI, as lift and drag gradually exchange
> dominance throughout the stroke, the net force on the blade remains
> perpendicular to the cord. Is this not correct? Most of the graphs of
> blade force I've seen show the resultant vector to be nearly
> perpendicular to the blade cord at all times during the stroke.
>
>>>
>>>> liken the early & late parts of the blade action to those of a
>>>> section of a propeller, then that side force relates directly to the
>>>> torque applied to drive the propeller. As with aircraft, rowing has
>>>> ways to cancel the effect of the side force, leaving only the axial,
>>>> propulsive force - in boats by having a blade on the other side,
>>>> working in mirror fashion.
>>>
>>>
>>> The side forces cancel out in that they (ideally) do no work. But
>>> they do not disappear insofar as stresses on the boat parts are
>>> concerned. Please correct me if I'm wrong here, Carl.
>>
>> But I've never noticed a boat getting hot, nor do they change
>> perceptibly in shape through the stroke. In fact, it is hard to
>> measure stresses in a rigger because they produce relatively small
>> amounts of elastic deformation. Much easier to strain-gauge an oar.
>
> That the boat elements do not deform, nor heat up, says more about the
> design of the boat & materials than the significance (or lack thereof)
> of the force, does it not? For level flight of an aircraft, the Lift
> force does no work. It is perfectly in opposition to the force of
> gravity on the aircraft. That Lift does no work does not mean that the
> aircraft does not endure the effects of its application.
>
> Your perspective is (respectfully) from that of a boat builder here. I
> am not trying to say that a "pinching" force exists to say that boats
> should be designed differently. Boats are obviously designed well
> enough to withstand it.
>
> However, if the net resultant force on the blade is perpendicular to the
> shaft (as you have agreed) then...
>
> Given a catch angle of 30deg,
> with an applied handle force of 577.5N
> With force applied at 30deg to the oar handle (due to reach of the
> rowers arms)
> perpendicular force on the oar handle from the rower is then
> Fph = 577.5cos(30) = 500N perpendicular to the handle.
> given a scull length of 280cm
> inboard of 80cm
> the force at the blade is then 200N, perpendicular to the shaft.
> At 30 deg oar angle, there will be
> Fsb = cos(30)*200N = 173.2N directed toward the boat, and
> Fdb = sin(30)*200N = 100N directed "forward" (direction of travel)
>
> So, If I'm wrong I really want to know, because I don't see anything
> erroneous there. If I've made a mistake somewhere in some assumption,
> or calculation I'd like to know exactly what it is, so that I can get it
> right for the future. Paul can't seem to point out my errors, so
> hopefully someone else can.
>
> To continue that calclulation... With a perpendicular oar force of 500N
> at the handle and 200N at the blade, the reaction of those forces at the
> pin is 700N with a direction perpendicular to the oar shaft.
>
> That means, at a 30deg oar angle, there is 350N applied to one pin that
> is driving the boat forward, and 606.2N applied to that pin pointing in
> toward the boat.
>
> I don't consider ~135lb of force at the pin pointed perpendicular to the
> long axis of the hull to be insignificant. Maybe it's not enough to
> deflect the pin or stress the riggers much, but it's about a coxswain's
> worth of force! :-) So, where is(are) my mistake(s)?
>
> (There is also a reaction from the axial component of the rower's
> applied force ("pressure against the pin"). But since it has no
> reaction against the water, it can't drive the boat and should be
> ignored for calculations of boat propulsion, but for calculations of pin
> deflection it could be included. It resolves to Frpa = 144.4i + 250j N
> where i is positive away from the hull, and j is positive from stern to
> bow.)
>
>>>
>>>> The side force, of itself, does no work because it (normally) moves
>>>> nothing. And there is no such thing as pinching the boat at the catch.
>>>
>>>
>>> Whether you want to call it "pinching" or "two opposing forces that
>>> do no work" the forces do exist, and since the boat parts are not
>>> perfectly incompressible, some lateral compression must occur. If
>>> not, please explain in more detail how this is so.
>>
>> As above, the movements are insignificant so the losses are similarly
>> insignificant.
>
> Well, I'm not really worried about the losses, or deflections. Only
> that there is a significant component of the blade force pointed at the
> hull, and that for oar angles greater than 45 degrees, this component is
> greater than the component of force which drives the boat forward.
>
> Paul has said that the component of force directed at the boat is "so
> small as to be insignificant". If my math, and mechanics have failed
> me, I'd sure like to know where. Because as far as I can tell, at the
> catch, the amount of force pointing toward the hull is greater than the
> amount pointing in the direction of travel.
>
> snipping the part on sailboats.... (great though it was).
>
> -Kieran

Now that we have a fluid dynamicist, an(other) engineer, and an
engineer/boat builder active in this thread... I'd really appreciate it
if any of you could offer some feedback on where if anywhere, I've
screwed up such that the sideways (inward) components of the forces on
the blade (and thus the pin) in the early part of the stroke are less
than what I've figured.

Thanks!

-Kieran


24 Feb 2007 14:35:42
Re: Lift and blade forces

On Feb 24, 2:12 pm, Kieran <[email protected] > wrote:
> KC wrote:
> > Carl Douglas wrote:
> >> KC wrote:
> >>> Carl Douglas wrote:
>
> >>>> The blade path has to be different, depending on whether there is a
> >>>> standing start or what passes in rowing for steady state. The
> >>>> question is; "How different?"
>
> >>>> At the static start you do not normally reach so far forward
> >>>> because, there being no forward motion, there can not yet be any
> >>>> component in the intended direction of the boat to give you a
> >>>> resolved flow along the blade. However, this being a transient flow
> >>>> situation, you do not get stall either - that takes some time to
> >>>> become established.
>
> >>> The confounding part of what you said Carl, is "the intended
> >>> direction of the boat". The boat must move for the blade to slide
> >>> through the water on it's lift-producing path, but it is not the
> >>> motion of the boat that is imperative to producing lift, it is the
> >>> motion of the blade away from the hull, through the water, that gives
> >>> us flow over the blade. Then of course there must also be some load
> >>> applied, for a lifting body in flow sans load produces no lift.
>
> >> You won't get flow _along_ the blade at a modest angle of attack, the
>
> > Okay... but I'd say that a modest AoA occurs *almost* instantaneously
> > once the oars are pulled upon by the rower.
>
> >> pre-requisite for generating lift on a foil, until you have forward
> >> motion. You can do the triangle if velocities as well as I can.
> >> Fortunately, you get rapidly increasing forward motion from the outset.
>
> >>>> A boat accelerates quite swiftly off the start, reaching ~60% (off
> >>>> my cuff) of eventual cruise velocity by the end of that first
> >>>> stroke, and its initial acceleration is greater than that. So you
> >>>> develop significant boat velocity very soon after the catch & lift
> >>>> will start to develop in that first part of the stroke. By the
> >>>> finish you will get the normal development of lift on the blade,
> >>>> following the mid-stroke stall phase (which may be somewhat
> >>>> extended, especially if you fail to dig deep enough in the middle to
> >>>> prevent air entrainment, which builds up rapidly &, because velocity
> >>>> is relatively low, has more time to do so.
>
> >>>> Naturally you will can resolve forces acting around a single blade
> >>>> not only in terms of lift & drag acting perpendicular to & along the
> >>>> blade, but instead to reveal a side force perpendicular to the boat
> >>>> & a propulsive force parallel to the boat, at both catch & finish.
> >>>> If you
>
> >>> The lift force is not actually perpendicular to the blade, it is
> >>> perpendicular to the free-stream flow. So if the angle of attack at
> >>> some point during the stroke is say, 7deg, then the lift vector will
> >>> be at an angle of 83 degrees to the blade cord, not 90deg.
>
> >> It is a convention that we talk about lift & drag forces as being
> >> mutually perpendicular, for which I blame the father of Cartesian
> >> coordinates. Lift forces operate perpendicular to every art of the
> >> surface of a foil (can't be any other way in a fluid), & the true lift
> >> vector is the sum of those local lift vectors (including the negative
> >> ones on the pressure face of the foil & any negative ones on the
> >> lifting face). Similarly with drag, which can only operate parallel
> >> to the local surface. But we opt to combine those forces into a
> >> single vector which we then resolve into lift, perpendicular to a
> >> chosen axis of the foil (easily determined for a symmetrical foil) &
> >> drag parallel to the same axis.
>
> > Hmmm... well, the way I recall it is that "lift" is *defined* as the sum
> > of the force components that are in the directions perpendicular to the
> > free stream flow.
>
> >>> However, the total resultant force acting on the blade (resultant of
> >>> drag and lift) is very nearly perpendicular to the cord of the blade,
> >>> and therefore also to the oar shaft.
>
> >> Sure, provided that lift predominates over drag, but nothing is for
> >> nothing.
>
> > Well, I was talking about the case of a rowing oar blade in the early
> > stages of the drive phase of a stroke. But anyway, drag predominates
> > over lift in the mid-stroke, yet the net force on the blade is still
> > perpendicular to the cord. AIUI, as lift and drag gradually exchange
> > dominance throughout the stroke, the net force on the blade remains
> > perpendicular to the cord. Is this not correct? Most of the graphs of
> > blade force I've seen show the resultant vector to be nearly
> > perpendicular to the blade cord at all times during the stroke.
>
> >>>> liken the early & late parts of the blade action to those of a
> >>>> section of a propeller, then that side force relates directly to the
> >>>> torque applied to drive the propeller. As with aircraft, rowing has
> >>>> ways to cancel the effect of the side force, leaving only the axial,
> >>>> propulsive force - in boats by having a blade on the other side,
> >>>> working in mirror fashion.
>
> >>> The side forces cancel out in that they (ideally) do no work. But
> >>> they do not disappear insofar as stresses on the boat parts are
> >>> concerned. Please correct me if I'm wrong here, Carl.
>
> >> But I've never noticed a boat getting hot, nor do they change
> >> perceptibly in shape through the stroke. In fact, it is hard to
> >> measure stresses in a rigger because they produce relatively small
> >> amounts of elastic deformation. Much easier to strain-gauge an oar.
>
> > That the boat elements do not deform, nor heat up, says more about the
> > design of the boat & materials than the significance (or lack thereof)
> > of the force, does it not? For level flight of an aircraft, the Lift
> > force does no work. It is perfectly in opposition to the force of
> > gravity on the aircraft. That Lift does no work does not mean that the
> > aircraft does not endure the effects of its application.
>
> > Your perspective is (respectfully) from that of a boat builder here. I
> > am not trying to say that a "pinching" force exists to say that boats
> > should be designed differently. Boats are obviously designed well
> > enough to withstand it.
>
> > However, if the net resultant force on the blade is perpendicular to the
> > shaft (as you have agreed) then...
>
> > Given a catch angle of 30deg,
> > with an applied handle force of 577.5N
> > With force applied at 30deg to the oar handle (due to reach of the
> > rowers arms)
> > perpendicular force on the oar handle from the rower is then
> > Fph = 577.5cos(30) = 500N perpendicular to the handle.
> > given a scull length of 280cm
> > inboard of 80cm
> > the force at the blade is then 200N, perpendicular to the shaft.
> > At 30 deg oar angle, there will be
> > Fsb = cos(30)*200N = 173.2N directed toward the boat, and
> > Fdb = sin(30)*200N = 100N directed "forward" (direction of travel)
>
> > So, If I'm wrong I really want to know, because I don't see anything
> > erroneous there. If I've made a mistake somewhere in some assumption,
> > or calculation I'd like to know exactly what it is, so that I can get it
> > right for the future. Paul can't seem to point out my errors, so
> > hopefully someone else can.
>
> > To continue that calclulation... With a perpendicular oar force of 500N
> > at the handle and 200N at the blade, the reaction of those forces at the
> > pin is 700N with a direction perpendicular to the oar shaft.
>
> > That means, at a 30deg oar angle, there is 350N applied to one pin that
> > is driving the boat forward, and 606.2N applied to that pin pointing in
> > toward the boat.
>
> > I don't consider ~135lb of force at the pin pointed perpendicular to the
> > long axis of the hull to be insignificant. Maybe it's not enough to
> > deflect the pin or stress the riggers much, but it's about a coxswain's
> > worth of force! :-) So, where is(are) my mistake(s)?
>
> > (There is also a reaction from the axial component of the rower's
> > applied force ("pressure against the pin"). But since it has no
> > reaction against the water, it can't drive the boat and should be
> > ignored for calculations of boat propulsion, but for calculations of pin
> > deflection it could be included. It resolves to Frpa = 144.4i + 250j N
> > where i is positive away from the hull, and j is positive from stern to
> > bow.)
>
> >>>> The side force, of itself, does no work because it (normally) moves
> >>>> nothing. And there is no such thing as pinching the boat at the catch.
>
> >>> Whether you want to call it "pinching" or "two opposing forces that
> >>> do no work" the forces do exist, and since the boat parts are not
> >>> perfectly incompressible, some lateral compression must occur. If
> >>> not, please explain in more detail how this is so.
>
> >> As above, the movements are insignificant so the losses are similarly
> >> insignificant.
>
> > Well, I'm not really worried about the losses, or deflections. Only
> > that there is a significant component of the blade force pointed at the
> > hull, and that for oar angles greater than 45 degrees, this component is
> > greater than the component of force which drives the boat forward.
>
> > Paul has said that the component of force directed at the boat is "so
> > small as to be insignificant". If my math, and mechanics have failed
> > me, I'd sure like to know where. Because as far as I can tell, at the
> > catch, the amount of force pointing toward the hull is greater than the
> > amount pointing in the direction of travel.
>
> > snipping the part on sailboats.... (great though it was).
>
> > -Kieran
>
> Now that we have a fluid dynamicist, an(other) engineer, and an
> engineer/boat builder active in this thread... I'd really appreciate it
> if any of you could offer some feedback on where if anywhere, I've
> screwed up such that the sideways (inward) components of the forces on
> the blade (and thus the pin) in the early part of the stroke are less
> than what I've figured.
>
> Thanks!
>
> -Kieran


I'm still finding your "quest" less than believable, when you still
manage to post things like this (after the above posting):

"On the other hand, at least during mid stroke almost all the force on
the blade (and pin) is pointing in the direction of travel. Whereas
earlier in the stroke at steeper oar angles when the blade is
producing
lift most effectively, much of the force is directed at the boat and
less in the propulsive direction. - KC"

You seem to be continuing to ask "Where have I gone wrong?", yet you
are the one with just the education to figure that out, aren't you?
I'm certainly not! Though my suspicions are in the direction that you
are not seeing the difference between the static and dynamic
situations. Since you have told me "They are not different." in so
many words. There is some additional irony in that you do see "clear
differences" when this sort of thing is discussed regarding the Erg,
and we can't agree there either. [:o)

Maybe this is not only "thick" irony, but deep too.

- Paul Smith



24 Feb 2007 22:49:08
Kieran
Re: Lift and blade forces

[email protected] wrote:
> On Feb 24, 2:12 pm, Kieran <[email protected]> wrote:
>> KC wrote:
>>> Carl Douglas wrote:
>>>> KC wrote:
>>>>> Carl Douglas wrote:
>>>>>> The blade path has to be different, depending on whether there is a
>>>>>> standing start or what passes in rowing for steady state. The
>>>>>> question is; "How different?"
>>>>>> At the static start you do not normally reach so far forward
>>>>>> because, there being no forward motion, there can not yet be any
>>>>>> component in the intended direction of the boat to give you a
>>>>>> resolved flow along the blade. However, this being a transient flow
>>>>>> situation, you do not get stall either - that takes some time to
>>>>>> become established.
>>>>> The confounding part of what you said Carl, is "the intended
>>>>> direction of the boat". The boat must move for the blade to slide
>>>>> through the water on it's lift-producing path, but it is not the
>>>>> motion of the boat that is imperative to producing lift, it is the
>>>>> motion of the blade away from the hull, through the water, that gives
>>>>> us flow over the blade. Then of course there must also be some load
>>>>> applied, for a lifting body in flow sans load produces no lift.
>>>> You won't get flow _along_ the blade at a modest angle of attack, the
>>> Okay... but I'd say that a modest AoA occurs *almost* instantaneously
>>> once the oars are pulled upon by the rower.
>>>> pre-requisite for generating lift on a foil, until you have forward
>>>> motion. You can do the triangle if velocities as well as I can.
>>>> Fortunately, you get rapidly increasing forward motion from the outset.
>>>>>> A boat accelerates quite swiftly off the start, reaching ~60% (off
>>>>>> my cuff) of eventual cruise velocity by the end of that first
>>>>>> stroke, and its initial acceleration is greater than that. So you
>>>>>> develop significant boat velocity very soon after the catch & lift
>>>>>> will start to develop in that first part of the stroke. By the
>>>>>> finish you will get the normal development of lift on the blade,
>>>>>> following the mid-stroke stall phase (which may be somewhat
>>>>>> extended, especially if you fail to dig deep enough in the middle to
>>>>>> prevent air entrainment, which builds up rapidly &, because velocity
>>>>>> is relatively low, has more time to do so.
>>>>>> Naturally you will can resolve forces acting around a single blade
>>>>>> not only in terms of lift & drag acting perpendicular to & along the
>>>>>> blade, but instead to reveal a side force perpendicular to the boat
>>>>>> & a propulsive force parallel to the boat, at both catch & finish.
>>>>>> If you
>>>>> The lift force is not actually perpendicular to the blade, it is
>>>>> perpendicular to the free-stream flow. So if the angle of attack at
>>>>> some point during the stroke is say, 7deg, then the lift vector will
>>>>> be at an angle of 83 degrees to the blade cord, not 90deg.
>>>> It is a convention that we talk about lift & drag forces as being
>>>> mutually perpendicular, for which I blame the father of Cartesian
>>>> coordinates. Lift forces operate perpendicular to every art of the
>>>> surface of a foil (can't be any other way in a fluid), & the true lift
>>>> vector is the sum of those local lift vectors (including the negative
>>>> ones on the pressure face of the foil & any negative ones on the
>>>> lifting face). Similarly with drag, which can only operate parallel
>>>> to the local surface. But we opt to combine those forces into a
>>>> single vector which we then resolve into lift, perpendicular to a
>>>> chosen axis of the foil (easily determined for a symmetrical foil) &
>>>> drag parallel to the same axis.
>>> Hmmm... well, the way I recall it is that "lift" is *defined* as the sum
>>> of the force components that are in the directions perpendicular to the
>>> free stream flow.
>>>>> However, the total resultant force acting on the blade (resultant of
>>>>> drag and lift) is very nearly perpendicular to the cord of the blade,
>>>>> and therefore also to the oar shaft.
>>>> Sure, provided that lift predominates over drag, but nothing is for
>>>> nothing.
>>> Well, I was talking about the case of a rowing oar blade in the early
>>> stages of the drive phase of a stroke. But anyway, drag predominates
>>> over lift in the mid-stroke, yet the net force on the blade is still
>>> perpendicular to the cord. AIUI, as lift and drag gradually exchange
>>> dominance throughout the stroke, the net force on the blade remains
>>> perpendicular to the cord. Is this not correct? Most of the graphs of
>>> blade force I've seen show the resultant vector to be nearly
>>> perpendicular to the blade cord at all times during the stroke.
>>>>>> liken the early & late parts of the blade action to those of a
>>>>>> section of a propeller, then that side force relates directly to the
>>>>>> torque applied to drive the propeller. As with aircraft, rowing has
>>>>>> ways to cancel the effect of the side force, leaving only the axial,
>>>>>> propulsive force - in boats by having a blade on the other side,
>>>>>> working in mirror fashion.
>>>>> The side forces cancel out in that they (ideally) do no work. But
>>>>> they do not disappear insofar as stresses on the boat parts are
>>>>> concerned. Please correct me if I'm wrong here, Carl.
>>>> But I've never noticed a boat getting hot, nor do they change
>>>> perceptibly in shape through the stroke. In fact, it is hard to
>>>> measure stresses in a rigger because they produce relatively small
>>>> amounts of elastic deformation. Much easier to strain-gauge an oar.
>>> That the boat elements do not deform, nor heat up, says more about the
>>> design of the boat & materials than the significance (or lack thereof)
>>> of the force, does it not? For level flight of an aircraft, the Lift
>>> force does no work. It is perfectly in opposition to the force of
>>> gravity on the aircraft. That Lift does no work does not mean that the
>>> aircraft does not endure the effects of its application.
>>> Your perspective is (respectfully) from that of a boat builder here. I
>>> am not trying to say that a "pinching" force exists to say that boats
>>> should be designed differently. Boats are obviously designed well
>>> enough to withstand it.
>>> However, if the net resultant force on the blade is perpendicular to the
>>> shaft (as you have agreed) then...
>>> Given a catch angle of 30deg,
>>> with an applied handle force of 577.5N
>>> With force applied at 30deg to the oar handle (due to reach of the
>>> rowers arms)
>>> perpendicular force on the oar handle from the rower is then
>>> Fph = 577.5cos(30) = 500N perpendicular to the handle.
>>> given a scull length of 280cm
>>> inboard of 80cm
>>> the force at the blade is then 200N, perpendicular to the shaft.
>>> At 30 deg oar angle, there will be
>>> Fsb = cos(30)*200N = 173.2N directed toward the boat, and
>>> Fdb = sin(30)*200N = 100N directed "forward" (direction of travel)
>>> So, If I'm wrong I really want to know, because I don't see anything
>>> erroneous there. If I've made a mistake somewhere in some assumption,
>>> or calculation I'd like to know exactly what it is, so that I can get it
>>> right for the future. Paul can't seem to point out my errors, so
>>> hopefully someone else can.
>>> To continue that calclulation... With a perpendicular oar force of 500N
>>> at the handle and 200N at the blade, the reaction of those forces at the
>>> pin is 700N with a direction perpendicular to the oar shaft.
>>> That means, at a 30deg oar angle, there is 350N applied to one pin that
>>> is driving the boat forward, and 606.2N applied to that pin pointing in
>>> toward the boat.
>>> I don't consider ~135lb of force at the pin pointed perpendicular to the
>>> long axis of the hull to be insignificant. Maybe it's not enough to
>>> deflect the pin or stress the riggers much, but it's about a coxswain's
>>> worth of force! :-) So, where is(are) my mistake(s)?
>>> (There is also a reaction from the axial component of the rower's
>>> applied force ("pressure against the pin"). But since it has no
>>> reaction against the water, it can't drive the boat and should be
>>> ignored for calculations of boat propulsion, but for calculations of pin
>>> deflection it could be included. It resolves to Frpa = 144.4i + 250j N
>>> where i is positive away from the hull, and j is positive from stern to
>>> bow.)
>>>>>> The side force, of itself, does no work because it (normally) moves
>>>>>> nothing. And there is no such thing as pinching the boat at the catch.
>>>>> Whether you want to call it "pinching" or "two opposing forces that
>>>>> do no work" the forces do exist, and since the boat parts are not
>>>>> perfectly incompressible, some lateral compression must occur. If
>>>>> not, please explain in more detail how this is so.
>>>> As above, the movements are insignificant so the losses are similarly
>>>> insignificant.
>>> Well, I'm not really worried about the losses, or deflections. Only
>>> that there is a significant component of the blade force pointed at the
>>> hull, and that for oar angles greater than 45 degrees, this component is
>>> greater than the component of force which drives the boat forward.
>>> Paul has said that the component of force directed at the boat is "so
>>> small as to be insignificant". If my math, and mechanics have failed
>>> me, I'd sure like to know where. Because as far as I can tell, at the
>>> catch, the amount of force pointing toward the hull is greater than the
>>> amount pointing in the direction of travel.
>>> snipping the part on sailboats.... (great though it was).
>>> -Kieran
>> Now that we have a fluid dynamicist, an(other) engineer, and an
>> engineer/boat builder active in this thread... I'd really appreciate it
>> if any of you could offer some feedback on where if anywhere, I've
>> screwed up such that the sideways (inward) components of the forces on
>> the blade (and thus the pin) in the early part of the stroke are less
>> than what I've figured.
>>
>> Thanks!
>>
>> -Kieran
>
>
> I'm still finding your "quest" less than believable, when you still
> manage to post things like this (after the above posting):
>
> "On the other hand, at least during mid stroke almost all the force on
> the blade (and pin) is pointing in the direction of travel. Whereas
> earlier in the stroke at steeper oar angles when the blade is
> producing
> lift most effectively, much of the force is directed at the boat and
> less in the propulsive direction. - KC"
>
> You seem to be continuing to ask "Where have I gone wrong?", yet you
> are the one with just the education to figure that out, aren't you?
> I'm certainly not!

Which is why I did not ask you (that time), and do not believe you when
you claim I'm wrong. I HAVE asked you to show where I am wrong, and you
are not capable, you only are capable of claiming I'm wrong without any
reasonable explanation as to how or why.

> Though my suspicions are in the direction that you
> are not seeing the difference between the static and dynamic

The first stroke vs. any other stroke, is less important to me. I'd be
happy to ignore the case of the first stroke and just have you prove
your claims for the "dynamic" case. Can you do that?

> situations. Since you have told me "They are not different." in so

Now who's misrepresenting whom? I stated very clearly that they are
similar, as in not very different. I never implied they were literally
identical.

> many words. There is some additional irony in that you do see "clear
> differences" when this sort of thing is discussed regarding the Erg,
> and we can't agree there either. [:o)

Hmmm... ironic indeed. Although I thought you said you did agree with
me (or part of what I said) after reading what I posted in that blog a
few weeks back. Still waiting for that reply/response, too. Email
would suffice.

-Kieran


24 Feb 2007 17:40:54
Re: Lift and blade forces

Big snip--

>
> > I'm still finding your "quest" less than believable, when you still
> > manage to post things like this (after the above posting):
>
> > "On the other hand, at least during mid stroke almost all the force on
> > the blade (and pin) is pointing in the direction of travel. Whereas
> > earlier in the stroke at steeper oar angles when the blade is
> > producing
> > lift most effectively, much of the force is directed at the boat and
> > less in the propulsive direction. - KC"
>
> > You seem to be continuing to ask "Where have I gone wrong?", yet you
> > are the one with just the education to figure that out, aren't you?
> > I'm certainly not!
>
> Which is why I did not ask you (that time), and do not believe you when
> you claim I'm wrong. I HAVE asked you to show where I am wrong, and you
> are not capable, you only are capable of claiming I'm wrong without any
> reasonable explanation as to how or why.

I really have tried, but you apparently do not appreciate the effort.
Can you prove I'm wrong in the claim I'm making?

Since you were unaware of my lnwledge of Ken Youngs Pages, perhaps you
are unaware of this one, that discusses the "worrisome "pinch-point"".
http://www.atkinsopht.com/row/bowangle.htm
Please do not take this as any sort of wholesale endorsement of the
entire Atkinsopht site, there is a lot there to disagree with, but
this particular bit might be applicable to our current discussion.
(His section regarding lift and drag doesn't seem to make sense to me,
so you might like it a lot, with your advanced level of understanding
and all.)

> > Though my suspicions are in the direction that you
> > are not seeing the difference between the static and dynamic
>
> The first stroke vs. any other stroke, is less important to me. I'd be
> happy to ignore the case of the first stroke and just have you prove
> your claims for the "dynamic" case. Can you do that?

Apparently not to your satisfaction, no. I can/do prove it to my own,
every time I am out in a boat with the tools in question at hand.

> > situations. Since you have told me "They are not different." in so
>
> Now who's misrepresenting whom? I stated very clearly that they are
> similar, as in not very different. I never implied they were literally
> identical.

--yawn-- Have you already forgotten about your claim that the blade
paths through the water were the same whether the boat is moving or
not. Which is a lot like arguing that since 2+2=4 and 2x2=4, that
3x3=6. Perhaps a "reasonable" argument could be made, it would just
be wrong!
This is tiresome, let's try to stay consistent, or it gets difficult
for me to follow.

> > many words. There is some additional irony in that you do see "clear
> > differences" when this sort of thing is discussed regarding the Erg,
> > and we can't agree there either. [:o)
>
> Hmmm... ironic indeed. Although I thought you said you did agree with
> me (or part of what I said) after reading what I posted in that blog a
> few weeks back. Still waiting for that reply/response, too. Email
> would suffice.
>
> -Kieran

Perhaps our agreement was insignificant to me. i.e. I think that you
mentioned something about how the mass of the moving head wasn't all
that critical in creating a "rowing simulation", which is what I had
argued long ago (remember, it's why I have a problem with using the
"static" and "dynamic" labels for Ergs), so of course I agree with
things that I have said, otherwise I keep my yap shut (and think about
it some more), for the most part. [;o)

- Paul Smith



25 Feb 2007 02:31:28
Kieran
Re: Lift and blade forces

[email protected] wrote:
> Big snip--
>
>>> I'm still finding your "quest" less than believable, when you still
>>> manage to post things like this (after the above posting):
>>> "On the other hand, at least during mid stroke almost all the force on
>>> the blade (and pin) is pointing in the direction of travel. Whereas
>>> earlier in the stroke at steeper oar angles when the blade is
>>> producing
>>> lift most effectively, much of the force is directed at the boat and
>>> less in the propulsive direction. - KC"
>>> You seem to be continuing to ask "Where have I gone wrong?", yet you
>>> are the one with just the education to figure that out, aren't you?
>>> I'm certainly not!
>> Which is why I did not ask you (that time), and do not believe you when
>> you claim I'm wrong. I HAVE asked you to show where I am wrong, and you
>> are not capable, you only are capable of claiming I'm wrong without any
>> reasonable explanation as to how or why.
>
> I really have tried, but you apparently do not appreciate the effort.
> Can you prove I'm wrong in the claim I'm making?

I have posted several links to sites which state that the net force on
the blade during the drive is nearly perpendicular to the blade cord.
That is all that's needed. If net force on the blade is perpendicular
to the blade, then there is a significant component of that force vector
pointing directly at the boat at steep oar angles. That's it, there's
nothing else to say really. Everything I know about the path of the
blade through the water, and how lift is generated, and every reference
I have read on the topic agrees with this. So, I have nothing else to
offer, unless someone can show me where my reasoning is wrong. If you
have done so, please re-state it, as I can think of nothing you've said
that indicates to me that net force on the blade is not perpendicular to
its cord. Your comments about back stays are pointless because back
stays are largely unnecessary, and most people could get by without
them. In fact, Vespoli delivered a brand new M2 pair (with wing
riggers) to me (my club really, but I was the coach using it) a couple
years ago, without back stays. I unwrapped the boat and riggers at US
Nationals in Indy, to find no back stays. I went to the Vespoli rep and
asked what was up, and he said they don't ship these boats with back
stays unless specifically requested, because they feel they are not
necessary. This was a mens heavyweight M2 2-, mind you... the same boat
they would have supplied to Olympic men had those men wanted a Vespoli.
So, the deflection of the pin is almost negligible.

Your thought experiment about a flexible pin is pointless unless you've
ever really rowed with such a pin. Regardless, since the force on the
pin is almost perpendicular to the oar shaft at all times ("almost"
because of the axial force from the rower pushing the button against the
gate) your "flexible pin" would deflect in a constantly changing
direction throughout the drive.


> Since you were unaware of my lnwledge of Ken Youngs Pages, perhaps you
> are unaware of this one, that discusses the "worrisome "pinch-point"".
> http://www.atkinsopht.com/row/bowangle.htm

I'm quite familiar with that page, and agree with its general point
about the pinch force. Note he does not say that it does not exist,
only that it does not waste any power. This is true because as Carl
pointed out, there's no work done by the pinch force, since there's no
deflection of the pin, and the pinch force on the other side of the boat
equally opposes it, so the boat does not move sideways, either.
Therefore since the applied force results in no motion, no work is done,
and therefore no power dissipated, and therefore there are no losses (no
waste) as a result of the pinch forces. But they do exist, and at steep
catch angles they are much larger than the forces pointing in the
propulsive direction.

> Please do not take this as any sort of wholesale endorsement of the
> entire Atkinsopht site, there is a lot there to disagree with, but
> this particular bit might be applicable to our current discussion.
> (His section regarding lift and drag doesn't seem to make sense to me,
> so you might like it a lot, with your advanced level of understanding
> and all.)

If his section on lift and drag doesn't make sense to you, where do you
get off making statements that imply you have a solid understanding of
lift and how it works? You spout off that "lift acts in the direction
we need it to" as if you're some expert on the subject. I don't claim
to be an expert but at least what I do say is based on textbook
knowledge of the phenomena of which I speak. You may think that your
observations back up your ideas of how something works, but don't forget
that two technical people here, one a fluid dynamicist just admitted to
not having realized that oars did not work primarily due to drag. You
may not see the pinch force, or its effects, or understand how or why it
is there, but that doesn't mean it's not significant and real.

>>> Though my suspicions are in the direction that you
>>> are not seeing the difference between the static and dynamic
>> The first stroke vs. any other stroke, is less important to me. I'd be
>> happy to ignore the case of the first stroke and just have you prove
>> your claims for the "dynamic" case. Can you do that?
>
> Apparently not to your satisfaction, no. I can/do prove it to my own,
> every time I am out in a boat with the tools in question at hand.

Great, then I ask politely and respectfully, please would you (again
since I've missed it sorry) state a detailed description of this proof
you see when you are rowing?

>>> situations. Since you have told me "They are not different." in so
>> Now who's misrepresenting whom? I stated very clearly that they are
>> similar, as in not very different. I never implied they were literally
>> identical.
>
> --yawn-- Have you already forgotten about your claim that the blade
> paths through the water were the same whether the boat is moving or

Please cut and paste where I said they are literally identical. I don't
think I ever said that. Much how you may have never said that the pinch
force doesn't exist, just that it's "so small as to be insignificant".
I did say that the SHAPE of the paths was VERY *similar*. But anyway,
let's let the case of the first stroke go by the way side. It doesn't
matter right now. I'm happy to focus on a moving-boat stroke.

> not. Which is a lot like arguing that since 2+2=4 and 2x2=4, that
> 3x3=6. Perhaps a "reasonable" argument could be made, it would just
> be wrong!
> This is tiresome, let's try to stay consistent, or it gets difficult
> for me to follow.
>
>>> many words. There is some additional irony in that you do see "clear
>>> differences" when this sort of thing is discussed regarding the Erg,
>>> and we can't agree there either. [:o)
>> Hmmm... ironic indeed. Although I thought you said you did agree with
>> me (or part of what I said) after reading what I posted in that blog a
>> few weeks back. Still waiting for that reply/response, too. Email
>> would suffice.
>>
>> -Kieran
>
> Perhaps our agreement was insignificant to me. i.e. I think that you

Well, it seemed significant to you at the time, and you said you were
going to post a follow up to my post.

-Kieran

> mentioned something about how the mass of the moving head wasn't all
> that critical in creating a "rowing simulation", which is what I had
> argued long ago (remember, it's why I have a problem with using the
> "static" and "dynamic" labels for Ergs), so of course I agree with
> things that I have said, otherwise I keep my yap shut (and think about
> it some more), for the most part. [;o)
>
> - Paul Smith
>


25 Feb 2007 16:46:13
Lawrence Edwards
Re: Vespoli boats

<[email protected] > wrote in message
news:[email protected]
> Sorry to contradict you Lawrence, but you must be either mistaken or
> have rowed the only 2 resolute with enclosed bulkhead.

It was a couple of years ago, so perhaps my memory is faulty. Do Resolute
manufacter different specification 8s perhaps? The boat we used was a few
years old, so I would guess it was made around 2000.




27 Feb 2007 02:11:57
Paul
Re: Lift and blade forces

I wasn't quite sure where to jump in on this, but here goes...

I am quite happy to admit that I am being really stupid here, but
surely what ever lift is created by the spoon as it moves sidways
(relative to the boat) in the water is pushing the spoon towards its
back side, ie towards the bow. This seems to me to be the opposite of
what we want, ie lift is our enemy not our friend. Please explain in
very sinple terms what is actually going on?