Shorter Oars
MelHa...@googlemail.com
article - perhaps someone with university access could give a precis?
Mel
Carl Douglas
From that precis, I have to wonder whether the central point has been
missed: that a more efficient oar must, inevitably, take longer to
complete the same stroke path as one of lower propulsive efficiency.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
Email: ca...@carldouglas.co.uk Tel: +44(0)1932-570946 Fax: -563682
URLs: www.carldouglas.co.uk (boats) & www.aerowing.co.uk (riggers)
paul_v...@hotmail.com
> MelHarb...@googlemail.com wrote:
> > An article that might be of interest. I haven't got access to the full
> > article - perhaps someone with university access could give a precis?
>
>
> > Mel
>
> From that precis, I have to wonder whether the central point has been
> missed: that a more efficient oar must, inevitably, take longer to
> complete the same stroke path as one of lower propulsive efficiency.
>
> Cheers -
> Carl
>
> --
> Carl Douglas Racing Shells -
> Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
> Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
> Find: http://tinyurl.com/2tqujf
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
Couldn't it likewise take the same amount of time, but propel the
system through a slightly greater distance? (to be deemed "more
efficient")
- Paul Smith
Charles Carroll
As a general rule I have always thought that you shorten the outboard to get
a higher rate. I thought this meant less time on the pins per stroke, but
more strokes per outing.
But as Carl is fond of telling us, everything in rowing is a compromise.
So if you were to add up the cumulative time you were on the pins per outing
what would give you the most time on the pins? Longer strokes but less of
them? Or shorter strokes but more of them?
I am not even sure this question makes sense.
Cordially,
Charles
Carl Douglas
I think not, Paul.
Your forward movement results from the application of a sustained force
to overcome the fluid resistance of boat in water plus any change in
kinetic energy of the system. Work is, of course, done in this process.
The force you apply will be the same for the efficient as for the
inefficient blade, but the duration will be less, due the greater
proportion of identical input work that is dissipated by the more
inefficient blade's messier interaction with the water.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
Carl Douglas
> Paul,
>
> As a general rule I have always thought that you shorten the outboard to
> get a higher rate. I thought this meant less time on the pins per
> stroke, but more strokes per outing.
>
> But as Carl is fond of telling us, everything in rowing is a compromise.
All life is series of compromises, but governed by principles on which
we should not, or cannot, compromise ;)
I should think that shortening outboard to raise rate was, depending on
where you started from, rather a bad idea. Most rowers have so may
other ways to increase rate that it is also likely to be unnecessary.
The only way we normally raise rate is by spending less time between
extraction & entry. How we do this determines how successful we are at
changing that rate & how much faster or slower we go as a result. Thus
a gallop to front-stops is likely to result in an increased hang over
front-stops at least long enough to negate any imagined benefit.
Similarly, a rushed thrust of hands away is of no benefit if it brings
with it a weakened or even a shortened finish, & less use still if you
still end up in that gallop forward.
The most efficient & rapid progress from finish to catch is likely to be
the smoothest, i.e. that with the lowest possible perceived
accelerations & decelerations of relative velocity between boat & crew.
The quickest catch will, obviously, be that which is preceded by the
least, or no, delay. The best finish is that which allows the blade to
remain well loaded closest to the end, & then the muscles to relax well,
before you reverse your actions to move to front-stops.
>
> So if you were to add up the cumulative time you were on the pins per
> outing what would give you the most time on the pins? Longer strokes but
> less of them? Or shorter strokes but more of them?
>
> I am not even sure this question makes sense.
>
> Cordially,
>
> Charles
It makes sense, but you have omitted the best answer from your list of
alternatives.
Your blade stays in the water for a time dependent on boat speed & arc
length (plus other variables such as catch angle & propulsive efficiency
- go shallow & the blade washes, is less efficient & is out sooner).
Long arcs make good propulsive sense provided that the boat is moving
fast but less sense (but an unquantified amount less) when it is moving
slower. Rates rise a little as work rate increases & brings increases
in boat speed, but only slightly since boat speed increases only with
the cube root of work rate. But stroke rates are strongly dependent on
recovery duration. So you'll get to spend the longest proportion of
your time pulling (as you say, on the pins) when you accomplish your
recovery in the least time, without disruption to your finish & with the
most immediate entry at the catch. And that will take the rate up,
which ought to lead you to lengthen your stroke arc as it increases your
speed.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
gregcr...@gmail.com
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
One would do well to remember that the oar isn't really "moving
through" the water insomuch as it is being anchored at one position,
locking up against a fairly resistant medium (water), slipping a bit
due to the arc of the application of leverage and the properties of
the medium (water), then being removed to repeat the process. The
whirling "puddle" you create stays in relatively the same position.
It's the boat that moves past it. Hence my sculling coach ages ago
told me "don't row too long in the same spot." ;)
Bigger blades and shorter rigs work for some, smaller blades and
longer rigs work for others. The last Olympics would seem to vote
heavily against a one-size fits all "bigger and shorter is better." In
face, looking at the top three finishes in the eights, "bigger and
longer" seems to be more prevalent among successful crews. That would
diverge sharply from Volker's hypothesis.
Volker's article in the most recent Rowing News may touch upon a
better theory: placement of the rower through the pin. Though this
still does not give the thumbs up to "bigger and shorter" blades. This
style of rigging has come around before, when blades were much
smaller, and it proved similarly successful for certain styles of
rowing.
As an interesting aside, the Croker sweep blade and the Concept 2 Fat
have very nearly the same 2-D profile area. Why is one rowed at
373-376 and the other at 365-368? Answer: there's a lot more than size
to be considered in the design. Identifying a blade as comparatively
"larger" does rather little to consider its behavior during the
stroke. So many other factors are at work.
Greg
uwcr...@gmail.com
<MelHarb...@googlemail.com> wrote:
> An article that might be of interest. I haven't got access to the full
> article - perhaps someone with university access could give a precis?
>
>
> Mel
Here is another study done at MIT in the early 1990's.
http://dspace.mit.edu/handle/1721.1/13423
Carl Douglas
Couldn't agree more that the objective is not to move blade through
water but to move boat past blade.
However, I cannot agree with the notion that the blade is static, or
should be, in the water. If your catch angle is 40 degrees from the
boat's axis, then the tip of a scull's blade moves outwards through the
water, away from the boat, by a distance of over 70cm/28", & to
accomplish that it really is moving, tip first through the water, at an
initial 3 - 4m/sec.
In the first part of the stroke the blade moves a considerable distance
_forward_. In this process it generates hydrodynamic lift & does not
noticeably slip (indeed, the term "slip" has no meaning during this
phase of the stroke). Nor does it add much velocity or energy to the
water since its lengthwise motion means that it exerts a relatively
slight influence across a rather large mass of water. When the blade
nears the square with the boat it does stall, dwells in a fixed zone of
water & then it does slip, dragging water with it & thus creating the
puddle which contains most of the lost energy which contributed nothing
to moving the boat. As you approach the finish, the blade starts to
move inwards, with water now flowing increasingly from root to tip &
lift is re-established, raising propulsive efficiency once more.
The net result is that the blade tip leaves the water markedly further
forward in the direction the boat is moving than it entered. And that
despite the slip which occurs in the mid-stroke when the puddle is being
created
>
> Bigger blades and shorter rigs work for some, smaller blades and
> longer rigs work for others. The last Olympics would seem to vote
> heavily against a one-size fits all "bigger and shorter is better." In
> face, looking at the top three finishes in the eights, "bigger and
> longer" seems to be more prevalent among successful crews. That would
> diverge sharply from Volker's hypothesis.
>
> Volker's article in the most recent Rowing News may touch upon a
> better theory: placement of the rower through the pin. Though this
> still does not give the thumbs up to "bigger and shorter" blades. This
> style of rigging has come around before, when blades were much
> smaller, and it proved similarly successful for certain styles of
> rowing.
>
> As an interesting aside, the Croker sweep blade and the Concept 2 Fat
> have very nearly the same 2-D profile area. Why is one rowed at
> 373-376 and the other at 365-368? Answer: there's a lot more than size
> to be considered in the design. Identifying a blade as comparatively
> "larger" does rather little to consider its behavior during the
> stroke. So many other factors are at work.
>
> Greg
Yes, it is still a very black art ;)
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Find: http://tinyurl.com/2tqujf
gregcr...@gmail.com
Sorry, Carl...but I'm only referring to the three key points: catch,
the furthest point out (...the moment of slip, approaching "square" as
you say), and finish. Most rowers barely understand one of those three
moments, but they at least flag important parts where the oar is
fundamentally engaging in a different activity. You can decorate the
tree with all the ornaments you wish in between, but I don't think it
will matter to most.
My real concern was to distinguish equipment differences from rigging
differences. I think there's more to mine with "through the pin"
positioning than with a 2-D comparative view of blade size. Anyone
rowing any blade could experiment with this, and it need not require
an industry to keep making blades bigger. A choice of blades sizes
should remain available, and thankfully, all companies continue to do
so.
kc
Somebody has hosted it here:
http://www.mediafire.com/?sharekey=0ce7430360eb1bb88ef1259ff1b60e81e04e75f6e8ebb871
I know not who. ;^)
Mike Sullivan
"Carl Douglas" <ca...@carldouglas.co.uk> wrote in message
news:73d5kmF...@mid.individual.net...
> gregcr...@gmail.com wrote:
>> On Mar 30, 1:57 pm, Carl Douglas <c...@carldouglas.co.uk> wrote:
>>> Charles Carroll wrote:
snip
> Couldn't agree more that the objective is not to move blade through water
> but to move boat past blade.
>
> However, I cannot agree with the notion that the blade is static, or
> should be, in the water. If your catch angle is 40 degrees from the
> boat's axis, then the tip of a scull's blade moves outwards through the
> water, away from the boat, by a distance of over 70cm/28", & to accomplish
> that it really is moving, tip first through the water, at an initial 3 -
> 4m/sec.
>
> In the first part of the stroke the blade moves a considerable distance
> _forward_. In this process it generates hydrodynamic lift & does not
> noticeably slip (indeed, the term "slip" has no meaning during this phase
> of the stroke). Nor does it add much velocity or energy to the water
> since its lengthwise motion means that it exerts a relatively slight
> influence across a rather large mass of water. When the blade nears the
> square with the boat it does stall, dwells in a fixed zone of water & then
> it does slip, dragging water with it & thus creating the puddle which
> contains most of the lost energy which contributed nothing to moving the
> boat. As you approach the finish, the blade starts to move inwards, with
> water now flowing increasingly from root to tip & lift is re-established,
> raising propulsive efficiency once more.
>
> The net result is that the blade tip leaves the water markedly further
> forward in the direction the boat is moving than it entered. And that
> despite the slip which occurs in the mid-stroke when the puddle is being
> created
Carl. I think you've explained this to us on RSR maybe a dozen
times, and I think this one is your most economical and clear explanation
I've read. I suspect this is because it's finally penetrating my thick
scull.
I understood it the first time explained to me, and understood it better
this time.
I have a question though, do you compose this explanation each time
or do you cut it and paste it in?
I'm not trying to be funny here, as sometimes I will do but I'm serious
as to whether you re-compose your understanding each time, or
if you are satisfied with the language of your explanation and cut
and paste in.
The reason I ask is that I find myself repeating myself often on usenet
and I always re-compose rather than repeat.
Mike
kc
> Couldn't agree more that the objective is not to move blade through
> water but to move boat past blade.
>
> However, I cannot agree with the notion that the blade is static, or
> should be, in the water. If your catch angle is 40 degrees from the
> boat's axis, then the tip of a scull's blade moves outwards through the
> water, away from the boat, by a distance of over 70cm/28", & to
> accomplish that it really is moving, tip first through the water, at an
> initial 3 - 4m/sec.
>
> In the first part of the stroke the blade moves a considerable distance
> _forward_. In this process it generates hydrodynamic lift & does not
> noticeably slip (indeed, the term "slip" has no meaning during this
> phase of the stroke). Nor does it add much velocity or energy to the
Might we be too caught up in terminology? This is an honest question,
as I know I am often guilty of it. So, I'm trying to see things from
the perspective of someone not familiar with all the "proper" terms...
Couldn't "slip" be considered a layman's description of what we would
more precisely call "angle of attack"? It's 1:20AM here so maybe I'm a
bit foggy-headed, but I don't see a problem with it, at first glance.
> water since its lengthwise motion means that it exerts a relatively
> slight influence across a rather large mass of water. When the blade
> nears the square with the boat it does stall, dwells in a fixed zone of
> water & then it does slip, dragging water with it & thus creating the
> puddle which contains most of the lost energy which contributed nothing
> to moving the boat. As you approach the finish, the blade starts to
> move inwards, with water now flowing increasingly from root to tip &
> lift is re-established, raising propulsive efficiency once more.
>
> The net result is that the blade tip leaves the water markedly further
> forward in the direction the boat is moving than it entered. And that
> despite the slip which occurs in the mid-stroke when the puddle is being
> created
I don't know why so many people keep pointing out that the blade exits
the water ahead of where it entered, as if this is some sort of proof
that hydrodynamic lift is happening. This is not evidence of lift. The
zero-lift locus of a blade with no force applied by the rower, passively
traveling through it's arc as the boat goes by, would indicate an exit
ahead of where the blade entered. Furthermore, a skydiver using a
para-foil style parachute takes great advantage of lift to maneuver, yet
still always travels toward earth. The fact that he does not
spontaneously fly away from earth does not mean there is no lift.
The main reason the blade exits the water ahead (toward the finish line)
of where it entered is because of the path required of it by its arc
about the pin combined with the forward travel of the boat. This has
nothing to do with lift on the blade. Lift happens because of this
path, not the other way around.
-KC. off to bed.
Carl Douglas
Fair question!
Like you, I am not economical. I try each time to re-assess what I say,
to find a better way of getting awkward concepts across, so it is likely
to come out a bit different.
I'm aware that RSR has an ever-changing readership & that individual
outlooks on the aspects of rowing which interest me most are also
changing, so while I may spout similar stuff from time to time the only
way it is cut & pasted is from of my crumbling brain.
Carl Douglas
> Carl Douglas wrote:
>
>> Couldn't agree more that the objective is not to move blade through
>> water but to move boat past blade.
>>
>> However, I cannot agree with the notion that the blade is static, or
>> should be, in the water. If your catch angle is 40 degrees from the
>> boat's axis, then the tip of a scull's blade moves outwards through
>> the water, away from the boat, by a distance of over 70cm/28", & to
>> accomplish that it really is moving, tip first through the water, at
>> an initial 3 - 4m/sec.
>>
>> In the first part of the stroke the blade moves a considerable
>> distance _forward_. In this process it generates hydrodynamic lift &
>> does not noticeably slip (indeed, the term "slip" has no meaning
>> during this phase of the stroke). Nor does it add much velocity or
>> energy to the
>
> Might we be too caught up in terminology? This is an honest question,
> as I know I am often guilty of it. So, I'm trying to see things from
> the perspective of someone not familiar with all the "proper" terms...
> Couldn't "slip" be considered a layman's description of what we would
> more precisely call "angle of attack"? It's 1:20AM here so maybe I'm a
> bit foggy-headed, but I don't see a problem with it, at first glance.
Fair point. I don't see angle of attack as in any way similar to slip,
although it is seductive to portray it as such. We rowers are
fundamentally simple folk, wanting to go faster despite our limited
talents & strength - we want bigger bangs for our bucks. So what we
should be most interested in is how much of our investment ends up
moving the boat & how much (the wasted rest) just makes pretty patterns
of turbulence & motion in the water.
When a foil "flies" through a fluid (air or water), of course it moves
that fluid. You could, I suppose, say that the gross movement of that
fluid might be termed "slip", but I think that would be quite wrong.
When a wing supports an aircraft it is possible for the wing & plane to
rise, fly level or go downwards, just by altering either the camber, or
the AoA, of that wing (within aerodynamically permissible limits, or
you'll stall & crash!). Increasing the lift to gain height will, to
sustain the same air-speed, necessitate an increase in power, but that
power increase may be largely explained by need to deliver the constant
increase in potential energy (increased height of heavy aircraft above
ground) implicit in the plane climbing. Similarly, your plane will
during the climb be giving a little bit more downwards momentum to the
surrounding stream-tube of air through which it is passing. That
carries away a bit more energy, but not a lot, because the essence of
fluid-dynamic lift is that it acts over large passing masses of the
surrounding fluid to give that a total amount of momentum but, through
the relatively small amount of velocity thus imparted, only modest
amounts of kinetic energy (& at a very economical penalty in terms of
fluid drag.
I think the fault is in us ever using the term "slip", but I also see
how natural that term is to a rower. That said, & as a trivial aside,
if you angled the blade sufficiently backwards on the shaft, at the
catch the blade would then slam forwards & inwards into the boat - would
the rower then regard that as slip?
Slip only seems to me to have value as a concept when we look at the
stall phase, & that's because fluid-dynamic lift is absent. What is
left is an increasingly (over time) foul & messy turmoil, with energy
being wildly dissipated into the bulk of the water all directions.
First there is the increasing amounts of velocity & hence KE imparted to
the small surrounding pool of water close to the blade, which is the
growing price necessarily paid in that phase for the reaction force
which continues to propel the boat. Then there are all the shearing
processes in which the edges of the blade rip & twirl the water
immediately passing them, giving away large amounts of input effort as
kinetic energy to numerous small packets of high-velocity water flows.
We can't easily measure the energy content of all those processes, at
least, not out on the river (yes, we could do so, maybe by analysing all
the local motions in 3D from some kind of stereoscopic recording of the
motions of suspended particles within that flow field, but I don't know
if that's been attempted). However, we can measure the relative motion
of teh blade & the rest of the river at a distance from it &, if we know
the force on the blade & the rate of that relative motion, we can then
calculate the rate of energy wastage through that "slip".
I don't disagree. But if the oarblade were used only when square with
the boat (as some seem to think it ought to be used - "'cos then it's
pushing the right way, not squeezing the boat", as they'd claim), you
wouldn't get that outcome. You'd find the blade leaving the water
further astern than it entered. The complex path actually taken by the
blade is a consequence of the flows being, for much of the stroke, not
transverse & all about drag, as the simplistic notion has it, but
lengthwise along the blade. That's why, as has been said before, the
blade path is so shaped. But it also provides the necessary conditions
for fluid-dynamic lift to be generated - just add a load to the blade &
lift will arise to resist it.
An unloaded wing can pass edge-on through air without generating any
lift. That's the same situation as for the unloaded oarblade on the
moving boat, being allowed to drop into the water & go where it will -
it follows the "tractrix" as it is sometimes called. The confusion
creeps in because the path of the _loaded_ blade, as with the path of
the loaded wing, may be only very slightly different from the path of
unloaded tractrix (until you reach the stall phase). And that seemingly
trivial, almost undetectable difference, which is so easily dismissed by
those who would deny the relevance of lift, is so because the actual
hydrodynamic loading of the loaded blade is really so very slight in the
early & later parts of the stroke - you don't get much change in AoA
under those loadings, so the blade's flight path under load hardly
departs, at first, from the tractrix (or locus, or path) of the unloaded
blade.
Please feel free to better explain that through which I have just stumbled.
kda...@kidare.com
<SNIP>
This is interesting.
A couple of months ago, I read a brief article by Andy Triggs Hodge
(GB4- stroke) about the technique exercises they did. One of their
coaches, Jonny Singfield, got them to do one exercise which Hodge
describes as putting the blade into the water at the catch then
holding it there for a "moment" (length unspecified) before taking the
stroke. This sounds alot like the advice Gordon Hamilton gave Charles
about waiting for the blades to come back to him before applying
pressure.
I had assumed that it was intended just to encourage patience and
relaxation at the catch. But thinking about the forward movement of
the blade through the water at the catch that you describe, I wonder
if allowing the water to flow briefly over an unloaded spoon creates
some lift _before_ load is applied, so that when it is applied, more
effort is effective. Catches which are loaded too quickly before some
lift has been generated (or even before the blade is fully immersed)
will result in greater slip and wasted effort.
I have tried the "catch and hold" method in our 4- (hold = c. 1/4 sec)
and (when done properly) I can attest to it improving the general feel
of the catch. Maybe this is why, or maybe I'm barking up the wrong
tree.
I have also tried it in a 1x with less success. With less momentum in
the boat, it seems to just mess up your catches.
Kit
Marco
It's amazing that everybody is talking about this but no one is
actually trying to replicate or to experiment with this.
I have been trying, with my limited resources, to test both oar shape
and different type of rigging to see which one is the most efficient.
Strangely this year I am focusing on oars length. Since it's really
hard to account for the variables I am trying to make as many pieces
as possible so I can reduce the amount of errors. So far it seems
that in my population (slow high school girls) the shorter length is
working to their advantage. I am now trying to find an optimal
inboard experimenting with different lengths in different boats (8+
and 4+).
I think we should start implementing a policy of numbers. Take your
crews down change one variable at the time and get results in your
hands and send them over.
The "I think" "higher rate" "lower rate" "faster" "slower" are terms
that mean nothing without a point of reference especially working in
an environment like water that behave so differently.
What are your thoughts?
Marco
Mike Sullivan
<kda...@kidare.com> wrote in message
news:9e0fbce1-034a-471f...@j39g2000yqn.googlegroups.com...
snip
> I have tried the "catch and hold" method in our 4- (hold = c. 1/4 sec)
> and (when done properly) I can attest to it improving the general feel
> of the catch. Maybe this is why, or maybe I'm barking up the wrong
> tree.
>
> I have also tried it in a 1x with less success. With less momentum in
> the boat, it seems to just mess up your catches.
Years ago an elite sculler I coached and I disagreed over this very thing.
I stuck to the 'hit the catch quickly' thing and he insisted he went better
with a much softer entry and a gradual pick up of the water. I have
no idea if his method helped him go faster or if it's why he was second
instead of first in the trials.
His rationale for it, though, was interesting. He claimed that since the
initial part of the drive 'pinched the boat', that it was wasted energy.
So if this is a better catch/drive and indeed he pioneered it, he did
it for wrong reasons! Of course I knew no better than he did.
My own experiments were very unscientific, I would run some mosquito
fleet workouts from my single w/ people training for nationals.
I would scull practicing that methodology and like you, got a lot
of positive feedback for how the boat felt. However, when we
did short pieces and I tried to compete, as the other singles started
to move on me, I found myself having to attack the catches more to
hold them, which was successful. I draw no conclusions from those
experiments.
I've always incorporated an 'accelerated drive' drill in my teaching
of competitive people, but explicitly not to get them to race that
way, but to learn to feel the connection, not rip at the water,
and to learn to maintain the drive impulse right to the finish.
Marco
>
> My own experiments were very unscientific, I would run some mosquito
> fleet workouts from my single w/ people training for nationals.
> I would scull practicing that methodology and like you, got a lot
> of positive feedback for how the boat felt. However, when we
> did short pieces and I tried to compete, as the other singles started
> to move on me, I found myself having to attack the catches more to
> hold them, which was successful. I draw no conclusions from those
> experiments.
>
deceptive.
I remember an episode of coaching a LWW 2x in a really windy day on
the stretch starting from Magazine beach to the Harvard Bridge. We
were doing a 4' x 4 x 3.
After the 1st set of 4' the 2x was barely breaking the 1000 m. marks
even with the tail wind. I asked to the rower what they thought. The
stroke said: "Damn it's so heavy at the catch!" the bow :"I don't
know coach, it feels great to me I thought we were flying!"!
This not only prove that different people use different "sensation" to
judge the performance, but also that they rarely are objective. The
short explanation was that the bow was totally missing the catch
rowing in when the stroke already took care of most of the load.
Needless to say the after she made the correction the boat felt to her
"extremely heavy" but they started going much faster.
Mike Sullivan
"Marco" <Marco.Bo...@gmail.com> wrote in message
news:30790f65-8576-4520...@e5g2000vbe.googlegroups.com...
snip
>
> How the boat "felt" it's a really subjective and might be really
> deceptive.
Indeed, I've very well aware of that. Also, some rowers who
row badly for a long time groove into that sensation, so not rowing
that way doesn't feel right.
Yet, when I'm teaching someone something, trying to modify their
technique I'll ask them how it feels and use it as positive feedback
that he MUST be doing it right. Most of the time it's true.
Many times we can trick ourselves into thinking we've taught something
well when we really haven't. We think: well I've spent time working
on this, of course it's better and during the process of teaching, you lose
the 'critical eye' that caused you to help them fix the problem in the
first place. I could tell blood curdling tales, but I'm afraid it'll
keep you awake at night!
kc
I'm sure Carl's busy composing a 10 page essay on this, so I'll be quick:
No lift without load. Can't be done, it's just plain physics.
Lift is the reaction force (Newton's 3rd Law) to the load. If you don't
load the foil (blade/wing) then you don't get lift, no matter what kind
of flow is passing over the foil. So at least two things are necessary
for a lift force to develop on a foil: 1) a load must be applied in the
opposite direction, and, 2) you must have a decent leading-to-trailing
edge flow. If you don't have #2, then the reaction force is more drag
than lift. If you don't have #1, then there just isn't a reaction force
at all.
> I have tried the "catch and hold" method in our 4- (hold = c. 1/4 sec)
> and (when done properly) I can attest to it improving the general feel
> of the catch. Maybe this is why, or maybe I'm barking up the wrong
> tree.
I'm all for drills that teach an oarsman to better feel the water,
especially around the catch. But make sure they are not exaggerated,
because a quick catch is still a good one.
-KC
kc
> <kda...@kidare.com> wrote in message
> news:9e0fbce1-034a-471f...@j39g2000yqn.googlegroups.com...
> On 31 Mar, 01:15, Carl Douglas <c...@carldouglas.co.uk> wrote:
> <SNIP>
>
>
> snip
>
>> I have tried the "catch and hold" method in our 4- (hold = c. 1/4 sec)
>> and (when done properly) I can attest to it improving the general feel
>> of the catch. Maybe this is why, or maybe I'm barking up the wrong
>> tree.
>>
>> I have also tried it in a 1x with less success. With less momentum in
>> the boat, it seems to just mess up your catches.
>
> Years ago an elite sculler I coached and I disagreed over this very thing.
> I stuck to the 'hit the catch quickly' thing and he insisted he went better
> with a much softer entry and a gradual pick up of the water. I have
> no idea if his method helped him go faster or if it's why he was second
> instead of first in the trials.
>
> His rationale for it, though, was interesting. He claimed that since the
> initial part of the drive 'pinched the boat', that it was wasted energy.
> So if this is a better catch/drive and indeed he pioneered it, he did
> it for wrong reasons! Of course I knew no better than he did.
A soft catch with a gradual build up is altogether different than what's
been described in this thread. Drilling to feel the catch, allowing
time for the blade to fully submerge, & engage the water, etc. You can
still hit it hard once the blade is fully submerged. I think this is a
drill that also helps avoid missing water at the catch.
-KC
Carl Douglas
No need for me to compose ;) I think you've said all that it needs.
>> I have tried the "catch and hold" method in our 4- (hold = c. 1/4 sec)
>> and (when done properly) I can attest to it improving the general feel
>> of the catch. Maybe this is why, or maybe I'm barking up the wrong
>> tree.
If you spend 0.25 sec with the blade in & waiting for something
interesting to happen, I'm sure it feels good (per the comments on the
person with late entry who thought their boat was flying) but you'll
have missed about 1/3 of your stroke's normal duration. So for
something like the same result as if you wasted none of your time,
you'll have to pull 50% harder for the rest of teh stroke.
(That's nice: I managed to include a decimal, a fraction _&_ a
percentage within 1 sentence!)
>
> I'm all for drills that teach an oarsman to better feel the water,
> especially around the catch. But make sure they are not exaggerated,
> because a quick catch is still a good one.
>
> -KC
>
>> I have also tried it in a 1x with less success. With less momentum in
>> the boat, it seems to just mess up your catches.
>> Kit
Indeed, as you'd expect. But returning to KC's last comment: what does
a better "feel" mean? Sounds to me like juju.
Let's get back to those crazy kayakers. The shape of their paddle blade
assists in developing lift during the near-vertical part of entry as
well as during the rest of their stroke. And take the single-paddle
types with their angled but flat paddles - canoeists proper - whose
stroke is to a very large degree about entry, the blade being angled
well forward & pressed down into the water & then back, & who do lots of
short crisp strokes rather than drawing way back past the body. No
hanging around to feel the water in any of that. All about making rapid
& positive engagement & doing so in the way which best develops that
connection resulting from the phenomenon of hydro-dynamic lift.
In short, I see neither place or need to encourage rowers to get all
touchy-feely about the water. If they get their entry right, so they
neither scoop nor back-splash to any meaningful extent (sure, we all get
tip-splash), then they can have load building throughout the entry &
doing so without hiatus. No, you mustn't hit it, as that will cleave
the water & put air in behind the blade where you need a fully liquid
connection. And the proportionality of oar flex to load means that,
however quick your reactions, you simply can't build load anything like
instantaneously.
The only "feel" you need is of an immediate connection, with force
acting in the propulsive direction, That comes from practice, which can
only be done on the water.
Rowcoach
Dreisigacker about the shorter oars because of more efficient spoons.
I have it on video and will try to do a transcript on training camp
next week. Keep an eye on www.arcrsa.blogspot.com
I think that often athetes and coaches get confused or do not explain
the terms adequately: Heavy vs connected - a spoon that is connected
and loaded up will always feel heavier, so if the spoon is connected
though a good arm hang and strong trunk postion a heavy feeling is
good.
Fast vs slipping - slipping spoons move quicker and feel faster. It is
quite hard to get an athlete to change their mindset to thinking about
how effectively the boat moves past the spoon vs how fast the rower
gets from frontstops to back stops. Very fast slide speed generally
means that something gave way in the arm, body, hip link.
The presentation from Peter show that the load on the more efficient
spoons with shorter oars is higher in the beginning because of the
increased effieciency of the spoon (lift etc) and then at the finish
of the stroke the oar is rotating faster beacuse of more speed
development - for more efficient spoon read Fat Smoothie and for less
efficient read Big Blade. I think that the problem with experienced
athletes rowing with these new shapes is that the subjective feeling
to an athlete rowing with the Fat smoothie will feel heavy in the
beginning of the stroke and lighter at the end compared to the Big
Blade they are used to.
Also "quick catch" can be quite misleading. What components are quick?
In which direction shoud these "quick" movements be? I feel that in
the vast majority of cases describing the catch as needing to be
"quick" or "quicker" just gets the crew to move faster into and out of
frontstops or to chop the spoon in. IMO the catch is about slipping
the spoon in as close to matching the speed of the boat as possible in
the horizontal direction, with a high vertical speed to bury the spoon
as fast as possible minimizing slip and maximising the angle left for
developing lift and load on the spoon.
Some other thoughts from various discussions with coaches about spoon
shape/length; Move back to the big blade (or in some cases coaches
that have not changed to any newer shapes) - Top athletes have rowed
with big blades successfully since the early 90's and want to stick to
what works for them. I.e. Spracklen, Grobler, Lau etc as well as
athletes that have rowed with those blades all their careers Tomkins,
Ginn, Redgrave, DEN 4- etc. When athletes develop their winning
stroke force profile they are used to an oar reacting in a certain way
during certain parts of the stroke. This becomes comfortable and feels
good. Trying to get a top athlete to change to a shorter oar/different
spoon that "feels" different and requires a different application of
speed and force is quite difficult as it makes them uncomfortable,
which is not condusive to high performance. So they continue to use
what feels good and they win because they are exceptional.
- Blade lengths etc - Look at all standard rigging charts. For School
8+'s they recommend 370-373's and international 8+ 375-378 so about a
1.3% difference. Now a reasonable schoolboy 8 will row about 6:20-6:30
on the ergo (±410w) and an international 8+ 5:40-5:50 (±520w) so about
27% difference in power. IMO this makes it amost impossible for
juniors to apply force in the same way as the seniors do, hence it is
not possible to really apply technique and biomechanics the same way.
Do the same for JW and its gets much worse
In one of the RBN newsletters a while back Valery presented some data
on what the ideal biomechanical lengths should be for various heights/
lengths and these are way off what is "recommended".
I believe that most of it still comes from older "non adjustable" days
and the mind set continues, or is handed down just as much as outdated
theories stick around in other areas of sport - latate is bad is a
good example.
Spracklen described a very important point when he was here in SA in
October when he was talking about his program "People copy without
understanding and then wonder why it doesnt work". This can probably
be applied to most areas of rowing and coaching. We are always too
quick to use what we see in a World Champs video or read in a FISA
rigging survey, or use a national squad training program and then copy
it. The problem is that 99.9% of coaches do not have access to the
people that row in those videos or use those rigs or train on those
programs.
We must seek to understand the reasons that boats move and then use
science combined with a bit of intuition to find what is best with our
indivuduals and crews. Do not be afraid to experiment. Get the athlete
to understand that you are looking of ways to make them faster. If it
doesnt work you can always go back.
Maybe what you find today will be rowing dogma in 50 years????
kda...@kidare.com
That's fine. I'm quite prepared to be wrong on the reason. I think
just performing the exercise encourages relaxation around the catch
anyway, which I suspect is the real reason for the improved feel.
>
> > I have tried the "catch and hold" method in our 4- (hold = c. 1/4 sec)
> > and (when done properly) I can attest to it improving the general feel
> > of the catch. Maybe this is why, or maybe I'm barking up the wrong
> > tree.
>
> I'm all for drills that teach an oarsman to better feel the water,
> especially around the catch. But make sure they are not exaggerated,
> because a quick catch is still a good one.
>
> -KC
Agreed. I think the exaggeration can be useful in making the point,
but you certainly don't want to be doing it so much that it becomes
ingrained.
>
> > I have also tried it in a 1x with less success. With less momentum in
> > the boat, it seems to just mess up your catches.
> > Kit
Kit
kc
few comments:
Rowcoach wrote:
> There was an excellent presentation at the FISA Conference by Peter
> Dreisigacker about the shorter oars because of more efficient spoons.
> I have it on video and will try to do a transcript on training camp
> next week. Keep an eye on www.arcrsa.blogspot.com
>
> I think that often athetes and coaches get confused or do not explain
> the terms adequately: Heavy vs connected - a spoon that is connected
> and loaded up will always feel heavier, so if the spoon is connected
> though a good arm hang and strong trunk postion a heavy feeling is
> good.
"Good arm hang" is another thing that is misleading, obfuscating, etc.
To me, those words imply that a rower should, in the early part of a
stroke, have straight elbows and "hang" from the oar so to speak. This
is not true. One of these days I'll submit for publication my thesis
that demonstrates this. A straight arm early drive is no better and
maybe a bit worse than one where the rower "grabs" at the catch and
progressively (if slowly at first) flexes the elbows throughout the
drive, when it comes to developing an optimal force profile. The
take-home message is that some rowers tend to row "flexed arm" and some
tend to row "straight arm" in the early drive, and it's not really worth
the coach's time to try to "correct" either one, as any benefit from one
style over the other is minimal. So long as you see a good catch, and
good connection throughout (i.e. no joint is failing to hold its pose
against the load, as in the case bum-shoving for example) then you've
got nothing to worry about. In the case of the elbows, if you were to
see the rower take the catch by "grabbing" (flexing the elbows a bit) at
the catch, then later in the stroke see his elbows straighten out under
load, then this would be bad. But my data show this just doesn't happen
(except maybe in the case of the very novice rower), despite what people
think about the leg & hip extensors being stronger than the elbow flexors.
> Fast vs slipping - slipping spoons move quicker and feel faster. It is
> quite hard to get an athlete to change their mindset to thinking about
> how effectively the boat moves past the spoon vs how fast the rower
> gets from frontstops to back stops. Very fast slide speed generally
> means that something gave way in the arm, body, hip link.
>
> The presentation from Peter show that the load on the more efficient
> spoons with shorter oars is higher in the beginning because of the
> increased effieciency of the spoon (lift etc) and then at the finish
> of the stroke the oar is rotating faster beacuse of more speed
> development - for more efficient spoon read Fat Smoothie and for less
> efficient read Big Blade. I think that the problem with experienced
> athletes rowing with these new shapes is that the subjective feeling
> to an athlete rowing with the Fat smoothie will feel heavy in the
> beginning of the stroke and lighter at the end compared to the Big
> Blade they are used to.
Not sure how it would feel heavier at the beginning and not heavier too
at the end?
> Also "quick catch" can be quite misleading. What components are quick?
> In which direction shoud these "quick" movements be? I feel that in
> the vast majority of cases describing the catch as needing to be
> "quick" or "quicker" just gets the crew to move faster into and out of
> frontstops or to chop the spoon in. IMO the catch is about slipping
> the spoon in as close to matching the speed of the boat as possible in
> the horizontal direction, with a high vertical speed to bury the spoon
> as fast as possible minimizing slip and maximising the angle left for
> developing lift and load on the spoon.
I feel that some coaches put too much emphasis on this concept of
"matching the speed of the water." This idea, when placed in the mind
of a developing rower, could/can/does lead to missing water at the catch
& losing out on some of the high-oar-angle (& high efficiency) portion
of the drive. I emphasize a long catch (within healthy anatomical
limits of the particular rower) that goes in as quickly as possible and
changes direction as quickly as possible. If these things happen, then
whether the blade exactly matched the water speed as it entered becomes
less important, and actually happens eventually as a consequence of the
rower seeking a catch that locks on quickly (no missed water) & occurs
at full compression, but doesn't have any feel of backwatering.
>
> Some other thoughts from various discussions with coaches about spoon
> shape/length; Move back to the big blade (or in some cases coaches
> that have not changed to any newer shapes) - Top athletes have rowed
> with big blades successfully since the early 90's and want to stick to
> what works for them. I.e. Spracklen, Grobler, Lau etc as well as
> athletes that have rowed with those blades all their careers Tomkins,
> Ginn, Redgrave, DEN 4- etc. When athletes develop their winning
> stroke force profile they are used to an oar reacting in a certain way
> during certain parts of the stroke. This becomes comfortable and feels
> good. Trying to get a top athlete to change to a shorter oar/different
> spoon that "feels" different and requires a different application of
> speed and force is quite difficult as it makes them uncomfortable,
> which is not condusive to high performance. So they continue to use
> what feels good and they win because they are exceptional.
Best argument against equipment technology development! Same could be
said of many sports (e.g. golf). If you're good, the equipment matters
less.
> - Blade lengths etc - Look at all standard rigging charts. For School
> 8+'s they recommend 370-373's and international 8+ 375-378 so about a
> 1.3% difference. Now a reasonable schoolboy 8 will row about 6:20-6:30
> on the ergo (±410w) and an international 8+ 5:40-5:50 (±520w) so about
> 27% difference in power. IMO this makes it amost impossible for
> juniors to apply force in the same way as the seniors do, hence it is
> not possible to really apply technique and biomechanics the same way.
> Do the same for JW and its gets much worse
I have struggled with this discrepancy in my coaching, on occasion too.
Yet, if you lighten the load for women proportionately to their
relative power, they complain that it's too light, and indeed they don't
row as well nor as fast. I haven't put a whole lot of thought into it,
but suspect that the muscle contraction force-velocity relationship, may
have something to do with it.
> In one of the RBN newsletters a while back Valery presented some data
> on what the ideal biomechanical lengths should be for various heights/
> lengths and these are way off what is "recommended".
>
> I believe that most of it still comes from older "non adjustable" days
> and the mind set continues, or is handed down just as much as outdated
> theories stick around in other areas of sport - latate is bad is a
> good example.
>
> Spracklen described a very important point when he was here in SA in
> October when he was talking about his program "People copy without
> understanding and then wonder why it doesnt work". This can probably
> be applied to most areas of rowing and coaching. We are always too
> quick to use what we see in a World Champs video or read in a FISA
> rigging survey, or use a national squad training program and then copy
> it. The problem is that 99.9% of coaches do not have access to the
> people that row in those videos or use those rigs or train on those
> programs.
>
> We must seek to understand the reasons that boats move and then use
> science combined with a bit of intuition to find what is best with our
> indivuduals and crews. Do not be afraid to experiment. Get the athlete
> to understand that you are looking of ways to make them faster. If it
> doesnt work you can always go back.
>
> Maybe what you find today will be rowing dogma in 50 years????
Great points.
-KC
Mike De Petris
> "Good arm hang" is another thing that is misleading, obfuscating, etc.
>
> To me, those words imply that a rower should, in the early part of a
> stroke, have straight elbows and "hang" from the oar so to speak. This
> is not true. One of these days I'll submit for publication my thesis
> that demonstrates this. A straight arm early drive is no better and
> maybe a bit worse than one where the rower "grabs" at the catch and
> progressively (if slowly at first) flexes the elbows throughout the
> drive, when it comes to developing an optimal force profile. The
> take-home message is that some rowers tend to row "flexed arm" and some
> tend to row "straight arm" in the early drive, and it's not really worth
> the coach's time to try to "correct" either one, as any benefit from one
> style over the other is minimal. So long as you see a good catch, and
> good connection throughout (i.e. no joint is failing to hold its pose
> against the load, as in the case bum-shoving for example) then you've
> got nothing to worry about. In the case of the elbows, if you were to
> see the rower take the catch by "grabbing" (flexing the elbows a bit) at
> the catch, then later in the stroke see his elbows straighten out under
> load, then this would be bad. But my data show this just doesn't happen
> (except maybe in the case of the very novice rower), despite what people
> think about the leg & hip extensors being stronger than the elbow flexors.
Well, Carl said this so many times in centuries... :-)
SD...@live.com
should the blade be designed as an aerofoil or waterfoil shape in
order to better take advantage of its sideways movement through the
water ?
Or maybe we should have a totally flat blade design that can cut more
easily sideways.
Do we really need a curved spoon shape at all ?
Without a clue,
Steve.
Dave Sill
Me too. I just can't visualize how hydrodynamic lift can help propel the
boat. I've read all of the threads here about it pretty carefully, but I
really need some kind of visual aid like an animation.
Aerodynamic lift is easy to explain (longer flow path over top of wing
causes reduced pressure above wing), but wings are static and moving in
a pretty straight line. The path of a blade in the course of stroke,
with respect to the direction of water flow is pretty complex.
But even people who do seem to understand it, e.g., Carl, don't have any
real idea how the oar should be shaped to maximize it.
-Dave
KC
Hmmm... I honestly don't think he's been any more vocal about this (nor
for a longer period of time) than I. I think this came up in
conversations here around 5 or six years ago.
-KC
Mike Sullivan
"Dave Sill" <da...@sill.org> wrote in message
news:73n6bpF...@mid.individual.net...
> SD...@LIVE.COM wrote:
>> Just to join in the never ending discussion on 'lift' in rowing ;
>>
>> should the blade be designed as an aerofoil or waterfoil shape in
>> order to better take advantage of its sideways movement through the
>> water ?
>>
>> Or maybe we should have a totally flat blade design that can cut more
>> easily sideways.
>>
>> Do we really need a curved spoon shape at all ?
>>
>> Without a clue,
>
> Me too. I just can't visualize how hydrodynamic lift can help propel the
> boat. I've read all of the threads here about it pretty carefully, but I
> really need some kind of visual aid like an animation.
I know what you mean. I learned it when I learned how to
paddle a K-1. By drawing away from the boat with the
wing paddle slowly you can actually feel and see the
lift forces in action. That helped me see how that's
possible in rowing, but still didn't get it.
Then this paper helped me a lot:
Ken Young, UW, 1997
http://www.phys.washington.edu/users/jeff/courses/ken_young_webs/208A/scull.lift.html
It's got pictures for me!
Mike
Mike Sullivan
"KC" <kc_...@sonic.net> wrote in message news:gr5q0m$dv7$1...@gist.usc.edu...
snip
>> Well, Carl said this so many times in centuries... :-)
>
> Hmmm... I honestly don't think he's been any more vocal about this (nor
> for a longer period of time) than I. I think this came up in
> conversations here around 5 or six years ago.
meow...
:^)
Mike De Petris
..<arms catch>...
> > Well, Carl said this so many times in centuries... :-)
>
> Hmmm... I honestly don't think he's been any more vocal about this (nor
> for a longer period of time) than I. I think this came up in
> conversations here around 5 or six years ago.
ouch, how old I am!
kda...@kidare.com
> S...@LIVE.COM wrote:
> > Just to join in the never ending discussion on 'lift' in rowing ;
>
> > should the blade be designed as an aerofoil or waterfoil shape in
> > order to better take advantage of its sideways movement through the
> > water ?
>
> > Or maybe we should have a totally flat blade design that can cut more
> > easily sideways.
>
> > Do we really need a curved spoon shape at all ?
>
> > Without a clue,
>
> Me too. I just can't visualize how hydrodynamic lift can help propel the
> boat. I've read all of the threads here about it pretty carefully, but I
> really need some kind of visual aid like an animation.
This may or may not help:
http://www.concept2.com/us/oars/pursuit/blade_path.asp
SD...@live.com
>
> - Show quoted text -- Hide quoted text -
>
> - Show quoted text -
Flat blade or curved blade? anybody?
Carl Douglas
Well, we can but try :)
Fluid-dynamic lift is caused by a complex of processes under which a
(generally) flattened object being moved approximately edge-on (or
nose-on) through a fluid can experience large forces perpendicular to
its motion.
Those "lift" forces, if not actively resisted, will deflect the object
from its original path. If the object is relatively mass-less, & if no
opposing forces (gravitational or otherwise) are applied to it, then it
will change direction in such a way as to reduce those lift forces to zero.
If, though, you alter the object's alignment but maintain its steady
direction of motion, that will alter the lift forces. Changing its
alignment one way will increase those forces - up to a certain limit, in
ways characteristic of the object's shape & dimensions, its velocity &
the fluid. Changing that alignment the other way will first reduce the
lift forces towards zero & then beyond, to act & start increasing in the
opposite direction.
Lift results from there being a difference in the shape of the flow
paths on the object's opposite faces, & from now on let's call that
object a foil. Fluids tend to want, if possible, to follow the shapes
of the surfaces past which they flow, unless those surfaces change too
abruptly or are too tightly curved.
Think in 2 dimensions & now imagine the flow is divided into many
parallel layers. If the flow has to accelerate, those layers will
become thinner (just as flow accelerates in a pipe where the pipe gets
narrower) & closer together &, conversely, if the flow goes slower those
layers become correspondingly thicker & more spread out. If the foil
surface to be followed on one is side convex but flatter or concave on
the other side, you may already guess how the separations between those
2 sets of streamlines are affected: over the convex surface the
streamlines get thinner, bunch together & flow faster to get past the
hump, while on the other side they either remain at their original
spacing if the surface is flat, or even spread out & slow down if the
surface in concave.
Now whence comes the energy to accelerate the flows into those tighter
streamlines? The short answer is that pressure energy in the fluid is
converted temporarily into that kinetic energy (energy of motion). The
KE increases (in proportion to the square of the velocity) while the PE
(the fluid's internal pressure) decreases correspondingly. So where the
flow moves faster, over the convex surface, the pressure exerted on that
surface falls, & falls most where the flow is fastest & the streamlines
tightest together. Similarly, any expansion of the streamlines on the
other face causes a fall in velocity & rise in pressure over that face.
The more concave the surface, the wider the streamlines will spread &
the more the flow will locally slow down The difference between these 2
resulting forces is called "lift" (because this process was first
thought through properly in relation to the operation of wings).
However, because KE increases with the square of velocity, the increase
in KE & fall in pressure in the convex side is always much greater than
any change from the smaller fall in velocity on the other side.
And that's why foils (wings & blades) have curvature! If you then
factor in the curved path followed by the blade (e.g see the reference
to the late Ken Young's seminal work, which is illustrated by the
sequence on the C2 website), it's clear you'll need to increase that
blade curvature.
Of course, none of these pressure differences occurs unless there's a
load on the foil to balance them. Otherwise, the foil must immediately
change its path to change the flow streamlines & thus to eliminate lift.
So lift can only exist when the foil is loaded or is constrained to
move in a certain path (which requires applied forces).
An inevitable consequence of generating force by interacting with a
fluid is that you will in some way move a little or a lot of that fluid.
How efficiently that force is generated is gauged by how slight that
resulting movement is. However, there is an inalienable rule: in fluid
motion resulting directly from a given amount of lift, the increase in
fluid momentum in the opposite direction to the net lift force will be
proportional to that force. Momentum is the product of [mass x velocity
change], so for the same amount of lift you either move a small amount
of fluid by a lot, or a proportionately larger amount by proportionately
less. So what's the problem - isn't it the same either way?
Definitely not! While the lift is directly proportional to the lateral
momentum change in the fluid, the kinetic energy gained by that fluid is
proportional to [mass x velocity change squared]. If you halve the mass
of fluid moved, it has then to be moved twice as fast for the same
momentum, but the energy invested in that total momentum change
increases by [0.5 x 2^2] - it doubles! To move the boat with the least
energy lost, the trick for saving energy losses is to move relatively
large amounts of water by very small amounts.
That's where lift comes to your aid. If you dig a blade in square with
the boat & pull, it tries to move face-first & has no other way to go.
It works against a small, initially static, pool of water which very
soon moves, shears & tears, quickly giving a large increases in velocity
to a small mass of water. In contrast, during the early part of the
stroke (as illustrated by Ken Young & by the C2 sequence) the blade
scythes tip-first through the water, never spending time in any
locality. It incurs relatively little frictional resistance to move in
that end-on way but, if loaded, the lift forces the blade can now
generate for only trivial changes in its path are so great that it
barely changes from the path it'd follow under zero load. The result is
that a much large volume of water gets a much smaller velocity change,
making that part of the stroke more efficient (= lower losses).
That's how wings work, why gliders with no help but the occasional
rising air current & why large aircraft can fly so fast & efficiently -
the wings are so well designed that they give rather small downward
velocities to the very large (& thus relatively massive) sheets of air
which, every second, pass directly over their upper surfaces.
I wonder if this account, if read through very slowly & several times
over, will help those now peering in confusion at all this scribbling
about what we call "lift"?