Re: He's at it again!
Tinus
> You may remember our old friend Caustic from his position on buoyancy
> a couple of years ago. Well, for our amusement, he's at it again: this
> time on the subject of "lift."
>
> http://www.rowingillustrated.com/boards/viewtopic.php?f=16&t=2925&p=4...
>
> "ultimately, the lifting force is minimal when the blade velocity with
> relation to the water is minimal. No matter how fast you catch, the
> whole purpose of the catch is to accelerate the blade in the opposite
> direction of the velocity of that boat. If you pause at the catch -
> the blades are moving forward at, say, 3 m/s. When you catch, they are
> travelling at 0m/s. When you pull through, because the boat is being
> accelerated, they will, at best, be moving sternward at some velocity
> very much less than even a 10th of 3m/s.
>
> A good catch is easy to spot, just looks (and hear) for three things -
> firstly, a symmetrical entry splash, and secondly a dark puddle, and
> thirdly a quiet entry.
>
> A lot of folks mistakenly assume that rotational velocity can be used
> in a lift equation without any kind of detriment - but this is not the
> case. Just because the blade is transcribing an arc at a particular
> rotational velocity, that velocity is not directly equivalent to a
> linear velocity. As an example, think of a rolling tire, and then a
> point fixed on that rolling tire. The tire itself will have a linear
> velocity in a particular direction. But the point on that tire is
> actually constantly changing its linear velocity - from 2x the tire's
> forward velocity to 0x. If we were to affix a wing on that point on
> the tire, would we then logically conclude that obviously it's the
> lift on the wing that is propelling the tire, even somewhat? Of course
> not.
>
> When taking this parallel over to a rowing arc, we can think of the
> boat+ oar itself transcribing the linear line of velocity, and the oar
> blade being a fixed point on part of an arc (a "virtual" tire). The
> rower takes the blade going at 1x forward speed, and accelerates it in
> the opposite direction to 0x speed, and then tries to accelerate it to
> the stern. In reality, the oar doesn't move too much - you can see it
> displaces from it's entry by about a foot - and the boat benefits from
> increased velocity.
>
> But nowhere in that situation is lift a major contributing factor; the
> initial, primary condition required to generate lift - i.e. a linear
> velocity element of appreciable magnitude - is never satisfied.
>
> As another analogy, if I throw a brick, is the lift generated from it
> being thrown keeping it aloft, of the fact that I imparted a very
> large initial force on it, accelerating it to a high velocity, and
> that it is taking much longer for gravity to pull it back down? I
> think that anyone would agree that in that scenario, the effect lift
> is having on the brick is essentially nil. If I were to throw the same
> brick in a perfect vacuum and with the same force, it would not travel
> appreciably farther.
>
> The whole lift thing started out as a pseudo-scientific marketing
> dribble by oar manufacturers. While they like to use "lift" to
> determine how come a bigger blade slips less, they ignore the very
> glaring fact that, surprise suprise, a bigger blade face is harder to
> push through water.
>
> finally, the very large, glaring hole in the whole lift theory is that
> it is not universal. Lift is a universal force, and that means that if
> I can find even one stroke out there that defies the lift theory, the
> lift theory is not correct. There exists one such stroke. your first
> one from a dead stop."
It might be useful to explicitly state that the entire piece is a
quote from the forum. They who omit reading the link (like me) might
believe that you wrote the entire piece as a response to the forum.
IPS
You may remember our old friend Caustic from his position on buoyancy
a couple of years ago. Well, for our amusement, he's at it again:
this
time on the subject of "lift."
http://www.rowingillustrated.com/boards/viewtopic.php?f=16&t=2925&p=49399#p49399
Here is but one of his posts in the forum which looks like it's
heating up nicely:
Carl Douglas
Ian, you're a terrible old stirrer. Fancy winding up the good &
sensible folk of RSR in that way! Shall we apply the acid test: add
some acidic HCl to neutralise silly old Caustic's NaOH & turn him into
salt .
His intention & lack of grasp is apparent throughout. But he doesn't
want understanding, just to bludgeon folk into his blind followers. If
you don't understand fluid dynamics it is easy to create bogus arguments
against its established facts - provided your audience also lacks those
same insights. Much of what fluid dynmaics tells us is very
counter-intuitive, making it that much easier for the obscurantist to
gull a captive audience. How sad!
His ramblings are so mad it's hard to know where to start. A flying
brick _does_ produce aerodynamic lift, but he doesn't see that lift may
not work in one direction only, nor against gravity. He doesn't see
that if the mass is high, the area for lift generation small & of highly
non-aerodynamic shape (e.g. a brick!), & the working fluid of low
density (air), then lift forces, although present, will have little
influence. Some fighter planes were said to have the aerodynamics of a
brick, but they did have wings. The wings, not found on bricks or pigs,
provided the lift to keep a hefty plane aloft while huge engines
overcame the aerodynamic drag. No glider (which, like bricks, lack
engines) resembles a brick.
I should add that, because drag on a brick doubtless exceeds any lift (&
a brick's lift will oscillate between up, down & sideways) it _will_ go
further if thrown in a vacuum. So he's comprehensively wrong. Let's
hope old NaOH never flies anywhere: if he's right, planes won't fly, or
if airborne must crash.
Next, his snide insult to oarmakers. I might think oars are not yet of
perfect design, but they ain't bad. This guy doesn't even understand
that oars don't "push" water - even though it's so easy, even from
visual evidence, to show how little & insufficient pressure there is on
the face of a working blade.
Oarmakers must know that their public, led by the spoutings of such as
NaOH, haven't a clue how oars work. People favour bigger blades becasue
a bigger bat has more drag than a smaller one in the stalled mid-stroke
phase. They want more area because such as Caustic tell them the
mid-stroke is the best, most efficient place to pull. That's pure Snake
Oil, there's no evidence for that claim, but evidence rarely concerns
snake oil salesmen. Oarmakers will offer the bigger blades the public
think they need, or lose business to those who do. However, thanks to
discussions long ago here on RSR, few oarmakers have zero grasp of the
relevance of hydrodynamic lift to oared propulsion. Never mind some now
irrelevant face features (spines, etc.), for centuries sweep oars &
sculls have been curved both ways over their back faces for very good
hydrodynamic reasons. Similarly, lugging oars are straight & have an
elongated diamond or elliptical section for similarly good lift-related
reasons. And those different shapes relate directly to the differences
in how they're used.
Too much of what NaOH rabbits on about is mere bombast & best passed
over. He fails to understand either the velocities, the forces or the
flows over a blade, though a bit of Googling could have spared his
blushes. But his closing swipe vividly displays his inept logic: he
falsely asserts something as both fact & precedent without a scrap of
evidence, then claims this proves hydrodynamic lift is a fantasy.
When absolutely static there is no forward motion, so there can't yet be
flow along the blade. The fluid drag initially generated by the
slightly moving loaded blade is, of course, the first force to give a
forward impetus. But the boat accelerates, & as it does so a triangle
of velocities is established: movement of blade about pin & movement of
pin across the water establishing a resultant water flow from tip to
root of blade. That flow is all it takes for lift to be generated (over
the back of the blade) & to displace drag as the prime force acting on
the blade. Then you approach mid-stroke where stall kills lift, at
which point (if you understand what's happening) you'll bury deeper to
prevent aeration from breaking the important tensile connection between
the back of the blade & the water. And as you approach the finish,
already a good way towards eventual cruising speed, lift re-establishes
itself as the main force resisting the load you put on the blade
But NaOH claims that the first instant of the first stroke is typical of
the rest. Even the Red Queen would think that irrational.
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)
Alasdhair Johnston
"It's not right, it's not even wrong."
Carl Douglas
> Wolfgang Pauli came up with the best dismissal of such deluded ideas:
>
> "It's not right, it's not even wrong."
>
>
So _that's_ Pauli's exclusion principle?
C
Steven M-M
> Alasdhair Johnston wrote:
> > Wolfgang Pauli came up with the best dismissal of such deluded ideas:
>
> > "It's not right, it's not even wrong."
>
> So _that's_ Pauli's exclusion principle?
>
> C
>
> --
> 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)
If you go to this forum, you’ll see that I have tried, to the limit of
my understanding, to explain lift to Caustic.
http://www.rowingillustrated.com/boards/viewtopic.php?f=16&p=49432#p49432
You may also note my impatience and decision to abandon the effort.
Carl and others may recall that some years ago when I was having some
difficulty understanding the concept of lift, I asked questions on
RSR. Anyway, I hope in my remarks the student did well by my
teachers.
Steven M-M
Carl Douglas
We might, Steven, have to mark you down just a point for that early
remark you made there on lift, hinting at a possibility at the catch of:
"maybe some positive pull towards the finish".
Trolls hide under bridges, just waiting for slips such as that
unfortunate addition to your sentence. No matter.
As another poster says, the photo NaOH introduced shows only a blade at
mid-stroke. Hence no flow along, & lots across. (And it's too shallow,
with a stupid great hole behind it).
NaOH evidently can't deal with moving objects & velocity triangles.
Must've hated maths lessons & dreaded simple geometry. But he had twin
gifts: he could ignore facts & logic & could browbeat all comers.
He takes "lift" to be a free energy source (like a perpetual motion
machine), not a natural process in which a fluid's internal pressure
falls as its flow bends around a convex surface. And he proposes that
the lift process, known to every student of fluid dynamics, exerts a
magical pull all of its own. (Perhaps you suckered him in?) Then he
shows this can't be so, & makes the illogical deduction that lift (&
history too?) is bunk. That's how Stalin dealt with those he disliked -
accuse them of impossible crimes, then kill, imprison or exile them
NaOH tells lies about established science, then accuses knowledgeable
people of telling lies. That's shameless demagoguery of the worst sort,
but relatively harmless provided he a) stays out of politics & b)
doesn't do it in the street & frighten the horses.
Rowing could use fewer such nutters.
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
John E
While wing paddles appear to be well established in the kayak world
they apparently need a significant change of technique (more
exaggerated vertical movements) in order to generate sufficient flow
across their, quite radical, aerofoil sections.
My questioning of whether there is a measurable similar effect in
rowing centre around the low speed the water must flow at over the
length of the blade and the fact that modern rowing blades are really
curved plates, rather than aerofoil sections. While I know that true
aerofoil sections are not necessary to generate lift if they are set
at an angle of attack to the fluid, this doesn't seem to the
mechanical system we have in rowing.
My doubts were really crystallised though when my crew mate Charlie
Hamlin held a blade in his hand and floated the head perpendicular to
a landing stage. He then vigorously pulled and pushed it away from and
towards himself with no sign of any sideways movement. If lift is not
discernable in that situation why would there be any measurable lift
generated during the rowing stroke?
I (genuinely) await enlightenment!
John Ewans
Steven M-M
>
> We might, Steven, have to mark you down just a point for that early
> remark you made there on lift, hinting at a possibility at the catch of:
> "maybe some positive pull towards the finish".
>
Carl, did I lose points because of the qualifying "maybe" or by
suggesting that lift may have a positive effect, rather than just
minimizing the negative effect of slip? On the C2 website that I cited
to provide a visual reference, the Brothers D state, "Phase 1: Forward
Blade Motion: The blade moves significantly forward, toward the finish
line."
Sadly, two weeks ago, one of those Trolls took the form of a submerged
log and poked a hole in my Staempfli 2x. I'll be spending some time
this fall and winter, learning more of your craft as I repair this
elegant old girl.
Steven M-M
Tinus
> Trolls hide under bridges, just waiting for slips such as that
> unfortunate addition to your sentence. No matter.
And they feed on large replies and attention making their efforts (for
whatever reason they are made) worthwhile.
Tinus
You should consider lift forces due to horizontal motion of the blade
instead of vertical motion. Lift forces analogue to the lift forces
with sailing.
John E
> instead of vertical motion. Lift forces analogue to the lift forces
I understand that in rowing we are talking about the horizontal motion
of the blade in the water generating lift forces that have a forward
element, unlike kayaking where vertical movements generate forward
forces. However I still need enlightening!
Carl Douglas
I'll try.
Whether you get lift will depend on the angle of attack. AoA is defined
as the angle between the major chord of the foil & the direction of
flow. The major chord is the line joining the extreme leading &
trailing edges of the foil.
A symmetrical foil (same but opposite shape both faces) generates no
lift in a flowing fluid when at zero AoA. Well, in fact both faces
develop lots of lift, but being equal & opposite this cancels out. Now
split that foil from leading to trailing edges. Either half will now
generate lift despite having zero AoA (which is why commercial plane
wings are that sort of shape - they have no need to fly upside-down.
And such a foil continues to generate lift even at modestly negative
(nose down) AoA.
But there comes a time when, with increasingly negative AoA, the lift on
a strongly asymmetrical foil also falls to, & then below, zero.
Now look at your oarblade. It's a very extreme asymmetrical foil - not
only is its tip (for this purpose it's leading edge) well off-line from
the blade root in relation to the shaft axis, but it's also hollowed out
on the non-lifting face. Thus it already has a negative AoA when held
flat to the water with blade on edge to push away by the handle, as you
describe. So you have no way to say whether that foil has little enough
negative AoA to still lift & move as you think theory tells you it
should, or if the AoA is just too far negative & will give it negative lift.
What to do? well, I just did the obvious. It's hissing with rain here
this evening but, in the cause of science & RSR, I took a sculling blade
& went to play on the bank. And what did I find, with the handle held
fairly near the water?
1. On the push away the blade developed a modest torque around the
shaft in the over-square direction, but it actually moved just slightly
towards the face side, even when I resisted the turning tendency.
2. On the pull back, the blade moved rather more in the backwards
direction - the way you might think it should when pushed away.
3. After a dozen or so cycles, the blade had swung about 60cm/2ft
towards the back face direction, due to each push giving less movement
than each pull.
What's the explanation? (Please remember that these are no-load
conditions, in which there are no face-on forces for lift to combat, so
the path of the blade will imply minimal lift trajectories).
1. As I indicated, the AoA on the push is so negative that, despite the
foil shape, any lift is "slightly the wrong way".
2. But on the pull it is obvious that, referring the the shaft axis,
the inboard end of the blade is more towards the back face of the blade
than the tip is. Lift being linearly proportional to A0A, this gives
the curved blade a very useful positive AoA to go with its convexity.
3. Thus we had slight negative lift on the push but significant
positive lift on the pull, so no wonder I found the blade progressively
moving one way - it was a very interesting ratcheting process.
I hope it can now be seen how confusing simple experiments can be if set
to look for things they're ill-designed to detect, & in highly
unrealistic circumstances. So, with al the greatest respect to Charlie
Hamlin (whom I know) this experiment is not capable of demonstrating or
disproving the existence & relevance of lift in rowing. The blade is
meant to be loaded, & when loaded is prevented from stalling (until near
the mid-stroke) by the water flows continually adjusting the blade's AoA
as axial flow slows down.
If that's insufficiently clear, please ask & I'll try to give beter
answers. No time right now, even to proof read.
Carl Douglas
Whereas if those who fully understand the folly of what has been said do
nothing, rowing techniques get moulded & deformed by know-nowt loud mouths.
John E
>as the angle between the major chord of the foil & the direction of
>flow. The major chord is the line joining the extreme leading &
Yes, I follow all that (I've done a lot of work on vehicle
aerodynamics in the past) however I struggle to see how a rowing blade
in action can be said to have a set angle of attack relative to the
water it is in when it has someone applying pressure to it with some
considerable force.
What you appear to see if you hang off a bridge is water spilling
around all the edges of the blade, which must mean that the
significant flow you would need along the length of the blade to
generate lift does not really exist.
What am I missing?
Paul
I think I am missing it as well. I have tried Carls experiment in a
single in the past and with the extra resistance of a boat to move
been unable to detect any appreciable lift. I am also not convinced
that at such high AoA even at the catch there is much lift. I am
afraid I am not very convinced by the Dreissigacker web site either.
They have lots of theory but apparently little if any data. I can’t
see that the diagram of the tap water running over a blade face
(vortex edge bit) has anything to do with lift but everything to do
with water tension versus gravity. I’m sure there is some lift there,
but whether is enough to measure in terms of boat speed, I remain to
be convinced until someone can show me some data
Paul
Carl Douglas
>> Whether you get lift will depend on the angle of attack. AoA is defined
>> as the angle between the major chord of the foil & the direction of
>> flow. The major chord is the line joining the extreme leading &
>> trailing edges of the foil, etc.
>
> Yes, I follow all that (I've done a lot of work on vehicle
> aerodynamics in the past) however I struggle to see how a rowing blade
> in action can be said to have a set angle of attack relative to the
> water it is in when it has someone applying pressure to it with some
> considerable force.
It can't. The AoA of any foiling object is a self-adjusting thing.
Thus if a wing is lightly loaded, for level flight it will have a small
AoA. Now suppose the loading is significantly increased (this is a
theoretical example, done this way round for convenience, but the
reverse of a sudden unloading would be more realistic); then the plane
will continue to fly but the AoA will increase &, unless the pilot
adjusts the controls, the plane will start a steady descent. So the
pilot pulls the stick back to restore level flight, which does _not_ (in
this simple instance) further adjust the AoA between the wing & the
oncoming air, although he will have to open the throttle slightly. He
has to increase power because the increased AoA brings a small increase
in aerodynamic drag. And just to complete the circular description,
that increase in power will match the rate at which the descending
plane's mass had been shedding potential energy (the energy component
due to its altitude in the earth's gravitational field).
So the AoA of a foiling oar (i.e. one that's properly buried & in the
1st or last 3rds of the stroke) is a self-adjusting thing, depending
only on the lengthwise flow velocity along the blade & the load applied
by the rower. Because an oar is really rather lightly loaded in these
phases, being sized more for maximum drag in the mid-stroke stall phase,
AoA does not actually change a lot. The only times AoA changes much is
just as the oar enters the stall phase & just as lengthwise flow
re-establishes itself after the stall, & that change is manifest in the
high rate of face-first slip during the stall phase (which generates the
puddle).
>
> What you appear to see if you hang off a bridge is water spilling
> around all the edges of the blade, which must mean that the
> significant flow you would need along the length of the blade to
> generate lift does not really exist.
>
> What am I missing?
What you are seeing may be:
1. too much of the stall phase
2. what happens when a blade is inadequately buried
3. and only the surface water flows (remember that stuff happening on
the surface is not what happens below that surface)
No surprise there, especially when crews are told it's wrong to "loom".
(Why do folk create magic rules & mantras without first testing what
they then dictate?)
What you do see when you film a blade that's adequately buried is what
I've described. And, as you see, what Charlie H and you thought you saw
is not quite what actually happens. Nor was it a meaningful
demonstration for or against the established physics of hydrodynamic
lift. Its first failing was that you can't have lift if you don't first
have load - which is true even when you go to pick up the dog.
Was all that guff of any help?
Carl Douglas
Paul -
I don't see how a sculler can hope to detect lift, any more than the act
of sculling being a meaningful way of measuring water density or
viscosity. Lift is one of the processes going on around your blade
which determines that it feels locked into the water, but without
elaborate experimentation you cannot say "I can see (or otherwise
detect) this thing called lift". Lift is the flow process occurring
over the blade (principally its convex back surface) which generates the
lowering of pressure across much of that surface which creates the force
that exactly counters the load you apply to the blade. You cannot reach
out into the water from your boat, grab a bit of lift & sample it.
Instead you'd have to attach pressure & flow sensors over the surfaces
of the blade, to show the flows & pressures which are consistent with
the established physics of the process of hydrodynamic lift.
Unless what "lift" is is understood, then as with the Hunting of the
Snark, you cannot go out & catch or identify it. You might just as well
say that in sculling we can disprove the existence of atoms, although I
think we all know that they are out there too.
I don't mean that to be in any way preachy, Paul, nor to give offence.
I know that you really do want to understand what I'm burbling on about
& I do greatly respect & appreciate your interest. But I wanted to try,
above, to cut through the tough barrier of misconception which can
completely prevent any of us from seeing what's beyond. Did I succeed?
Let's end by saying that if you suddenly lose lift on a foil when you
weren't expect it, then you really do know something has gone badly
wrong. One stark example would be the stalling of an aircraft's wing -
when that happens the plane does suddenly fall, or at least its flight
angle turns smartly downwards. Another would be when a heavily-loaded
rudder on a sailboat either stalls or loses lift through aeration (air
getting sucked down from the water surface into the low-pressure zone
generated by the high lift forces central to the operation of any rudder
system) upon which the boat suddenly goes out of control & changes
direction. And the one that happens under our noses is the transition
from lift to stall that brings the sudden midstroke slippage of your
blade - but we are so accustomed to how a blade feels we don't realise
this is actually what is happening.
John E
> It can't. The AoA of any foiling object is a self-adjusting thing.
I was really querying whether a useful angle of attack existed, not
whether it varied. It is clear that if it exists it would vary, given
the dynamics of the stroke.
> What you do see when you film a blade that's adequately buried is
what
> I've described. And, as you see, what Charlie H and you thought you saw
> is not quite what actually happens.
That seems to get at the heart of the issue, which is whether there is
a useful amount of flow along the blade near the catch and finish in
an actual rowing stroke. Presumably these films were of an actual
rowing stroke, not a fixed blade in a ‘tank test’ ? If so are there
any links on the web?
I would love see one to learn more.
Carl Douglas
Again I think you are looking for the wrong thing. Thus, how do you
define what will be a useful AoA for an oarblade. As I've said, & as
even my simple last night's tests tend to support (anyone bother to
repeat them?), an asymmetric foil will generate lift down to distinctly
negative A0As.
Next, you are dealing with a dense fluid, a large foil & low area
loadings on that foil (no rower will believe it, but all their vast
effort produces only piddling area loads, which is why even badly buried
& highly aerated blades slip can still propel your boat).
Now let's do an over-simple sum on fluid velocity over the blade:
Assume initially that you take the catch parallel with the boat (no, no
one does, but it sets an upper limit to our study).
So fluid velocity = boat velocity.
Say velocity at catch = 4m/s, what's the Reynolds number for the blade?
* Re = water density x velocity x blade length/ water viscosity
* for a blade 0.5m long, that gives Re = 2,000,000
* (using Re equivalence, that's like the same foil moving at ~60m/s or
135mph through air, so it relates directly to what you might encounter
in automobile aerodynamics)
* at _zero_ AoA, for a NACA 5-series 12% chord wing (23012), 0.2 span (I
said it was crude!), that gives about 100N (=10kg force or 22lb force)
of lift in water
* at 1-deg AoA, the lift has doubled (& the drag is under 3% of the lift)
* the lift of that puny foil at that A0A in air at 60m/s would be a not
insignificant 5kg f.
* and lift will rise at the same rate for each additional degree of AoA.
May I rest my case and leave you to repeat the exercise for blades at
60, 45, etc, degrees ahead of perpendicular? I think you'll find
there's ample flow & lift, & rather small AoAs needed, until you get
past 30 degrees - at which point the blade, depending on loading, will
start to stall.
A number of films have been made, and in particular by the late, sadly
lamented Ken Young (I'm sure you can dig out his lectures on this, with
time-lapse photos & plots, as I think another RSR regular has preserved
what was on Ken's website).
Gotta go! Couldn't someone else crunch some numbers, do some
experiments & generate some answers, or is RSR only a sponge for this
sweaty brow? Methinks that most of rowing is unduly scared of engaging
its intellectual capabilities in pursuit of better performance. Please
remember that rowing is a physical & intellectual activity, not a
treasured belief system for the devout followers of an unchangeable
orthodoxy ;)
John E
> define what will be a useful AoA for an oarblade.
I just meant ones that are within a range that might be of use to
generate lift!
> A number of films have been made, and in particular by the late, sadly
> lamented Ken Young (I'm sure you can dig out his lectures on this, with
> time-lapse photos & plots, as I think another RSR regular has preserved
> what was on Ken's website).
This seems to be the film you mean, which is certainly interesting:
http://neutrino.phys.washington.edu/~wilkes/post/temp/phys208/scull.lift.html
I might do an experiment or two to see if one can actually see what
happening on the blade face.
Carl Douglas
>>> Again I think you are looking for the wrong thing. Thus, how do you
>> define what will be a useful AoA for an oarblade.
>
> I just meant ones that are within a range that might be of use to
> generate lift!
I really don't know what else I can do to make it easier for you, John.
I've given you the typical speed zone, Reynolds number & relationship of
lift to AoA in that environment for an oar-like foil. You say you've
been involved in car aerodynamics, so I showed you the corresponding
conditions for that environment & that an oar was operating in a flow
regime (by Re similarity) that's way up in the area where the
aerodynamic lift process is so influential.
There is an applied load, by you, on the blade. I am aware of no other
sources of fluid resistance remotely sufficient, during the foiling
phases, to carry the loads you apply to the blade, but the lift process
is immediately available & active. You can see the amount of slip
during mid-stroke.
I've shown you how small is the necessary AoA to sustain the applied
loads that lift on a blade needs to balance.
And you say you understand that AoA is self-adjusting to applied load.
So on what grounds would lift _not_ be providing the countervailing force?
>
>
>> A number of films have been made, and in particular by the late, sadly
>> lamented Ken Young (I'm sure you can dig out his lectures on this, with
>> time-lapse photos & plots, as I think another RSR regular has preserved
>> what was on Ken's website).
>
> This seems to be the film you mean, which is certainly interesting:
>
> http://neutrino.phys.washington.edu/~wilkes/post/temp/phys208/scull.lift.html
>
> I might do an experiment or two to see if one can actually see what
> happening on the blade face.
Not on what is conventionally termed the blade the face, please, John.
What matters is what happens over the convex back of the blade, even
during blade stall.
John E
One could mis-read that as being (amusingly) patronising, but it is
not a question of making it easy!
The issue is still whether in a real rowing stroke you do get flow
along the length of the blade near the catch and finish (on both
faces) because, if you don't, there is no possibility of lift. Ken
Young's film is interesting, and his conclusions are probably right,
but it would be of particular interest to see what the water is
actually doing on the blade faces throughout the stroke.
A Rowing Illustrated contributor points to http://cat.inist.fr/?aModele=afficheN&cpsidt=22038909
so I may buy that as this seems like an ideal problem for CFD
analysis.
Tinus
> > I really don't know what else I can do to make it easier for you, John.
> One could mis-read that as being (amusingly) patronising, but it is
> not a question of making it easy!
> The issue is still whether in a real rowing stroke you do get flow
> along the length of the blade near the catch and finish (on both
> faces) because, if you don't, there is no possibility of lift. Ken
> Young's film is interesting, and his conclusions are probably right,
> but it would be of particular interest to see what the water is
> actually doing on the blade faces throughout the stroke.
> A Rowing Illustrated contributor points tohttp://cat.inist.fr/?aModele=afficheN&cpsidt=22038909
> so I may buy that as this seems like an ideal problem for CFD
> analysis.
This entire thread looks much too complicated.
Lift very simply defined as the component of force perpendicular to
the direction of movement. It is easily experienced when moving a flat
plate trough water (or when making a crab). The water will change the
enforced motion. Drag will resist the motion, lift will alter the
direction of the motion. If you feel forces which alter the direction
of motion which you try to apply to the plate then you experience lift
forces. If you do this experiment then you will experience that
considerable lift forces exist when the angle of attack (AoA) is about
45 degrees.
The entire discussion in this thread should not focus on whether or
not lift exists (it is not magic) in the case of a rowing blade. It
should focus on getting a grasp of the motion of the blade. The
previously discussed video is a good example. However, it does not
show the position of the blade. An example of a clear picture is this
one: http://sanderroosendaal.files.wordpress.com/2010/07/blade.png
(this also includes the recovery so don't mention the stretched
piece). The blue line shows the direction of movement the red line the
position of the blade.
In rowing the AoA ranges from close to zero (catch) to 90 degrees*
(oar perpendicular to boat) and eventually back to zero (release). So
the blade goes trough all possible AoA during which lift force is
involved for a considerable period of time.
Velocity and flow is highest around these end points and lowest at the
perpendicular. Also, even if there would be no flow at one side of the
blade there would still be blade (lift) force.
Also nice to mention. Increasing the lift force is important because
the lift force does not apply any mechanical work on the medium/water
(by definition). This is what makes the lift force very efficient in
propulsion.
* or depending on convention -90 degrees
Walter Martindale
> > > Again I think you are looking for the wrong thing. Thus, how do you
> > define what will be a useful AoA for an oarblade.
>
> I just meant ones that are within a range that might be of use to
> generate lift!
>
> > A number of films have been made, and in particular by the late, sadly
> > lamented Ken Young (I'm sure you can dig out his lectures on this, with
> > time-lapse photos & plots, as I think another RSR regular has preserved
> > what was on Ken's website).
>
> This seems to be the film you mean, which is certainly interesting:
>
>
> I might do an experiment or two to see if one can actually see what
> happening on the blade face.
I've taken crude angle measurements of some elite scullers at the
catch - these ones have been in "A" finals at various world or Olympic
champs, and I've really only taken these measures on ones that have
(in the past) won or "placed". The videos were shot during training,
not all by me.
They really fast scullers get their scull shafts around to 70 degrees
past perpendicular to the boat, or to 20 degrees short of parallel to
the boat.
The blade tracks towards the finish line under the water for the first
30-60 cm of the stroke.
These are things I've observed using SiliconCoach software on video
shot from bridges, or in the case of Karpinnen's overhead photo, from
a photo (the angle of attack, no way to know what happened next).
That help with AoA info?
W
Carl Douglas
>> I really don't know what else I can do to make it easier for you, John.
>
> One could mis-read that as being (amusingly) patronising, but it is
> not a question of making it easy!
That you would be misreading it, & patronising is never amusing. I
recognise the good intellects of RSR readers but know that most are not
fluid dynamics experts. So I try to help explain the knotty science
within my expertise without jargon & maths. Making it as easy as
possible does matter & I always try to answer questions thus.
You do understand this field, or I'd not have mentioned the Reynolds
number similarity of blades with race car foils. I'd thought you'd see
(without over-explanation) that the AoA of a loaded blade must
self-adjust to the conditions (as on any wing), making queries about AoA
redundant. And because the blade a) generates lift even at negative AoA
& b) substantially increases its lift for single-digit rise AoA, I'd
thought we needn't review exact AoAs.
>
> The issue is still whether in a real rowing stroke you do get flow
> along the length of the blade near the catch and finish (on both
> faces) because, if you don't, there is no possibility of lift.
Why would you not get lengthwise flow when the blade is being driven
tip-first into the water by the forward motion of the boat, & is
rotating about the pin? If you drop the blade in & let it swing freely
it follows much the same path as when loaded. Are you really suggsting
that in the early & late stages of that undriven arc the flows are other
than parallel with the blade? I doubt it.
Ken
> Young's film is interesting, and his conclusions are probably right,
> but it would be of particular interest to see what the water is
> actually doing on the blade faces throughout the stroke.
As I said, I try to provide answers.
>
> A Rowing Illustrated contributor points to http://cat.inist.fr/?aModele=afficheN&cpsidt=22038909
> so I may buy that as this seems like an ideal problem for CFD
> analysis.
The final sentence of that synopsis does surprise me:
"Drag and lift coefficients calculated for the blade during a stroke
show that the transient hydrodynamic behaviour of the blade in motion
differs substantially from the stationary case."
Surely it's unsurprising that the fixed position in a flow means
reatively little when the constantly changing alignment of the blade to
the direction of the boat renders flows highly transient?
Years past, a UK oarmaker had tests done in a flume with the blade fixed
square to the flow & offered this as meaningful proof of his product's
superior performance. Yet he offered no results on a real stroke, nor
on the effects of depth variation. I have conducted detailed testing of
the effects of blade depth on drag & aeration of a square blade (funny
what one does when curiosity is raised, one doesn't mind getting hands
dirty & really wants to understand processes on which others only want
to prognosticate). FWIW, I've also discussed the full rowing stroke
with people offering CFD solutions - who found it logical (as do the
other fluid dynamicists I've chattd with) that the blade operates as I
have so often described here. At that time they agreed the model was
basically correct, but to analyse it by CFD would be rather harder than
sending a man to the moon. I'm sure CFD capabilities have advanced
hugely in the intervening 15 years, but it will be essential to have
realistic CFD model & boundary conditions before spending megaflops on
the exercise. Especially when the mass of the sport remains determinedly
sure that you row by pushing water.
In short, it's a fine subject for CFD, but we have easier ways
immediately to hand to get real answers, & with real models - but maybe
getting real data the wet way at low cost is less impressive these days?
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing low-drag Riggers/Advanced Accessories
Write: Harris Boatyard, Laleham Reach, Chertsey KT16 8RP, UK
Paul
The thing that interests me is not if lift exists, where it is at its
maximum etc. Even a dullard like me can grasp the basics. What is of
real interest is whether I should pay money for things like vortex
edges on my blades. To make that decision I need to see some data.
Something the blade manufacturers seem unable or unwilling to supply.
Paul
Tinus
So you agree about lift force. This splits the discussion. You don't
consider the amount and importance of lift force but instead the
difference in lift force.
Blade energy loss (drag) is about 15% of the total mechanical work
applied by the rower. This means that a reasonable amount of energy
can be gained by improving blade characteristics. I don't believe this
is questionable from a technical point of view.
Maybe the following could be the case: Of course blade manufacturers
don't show the data. The numbers might technically be significant and
possibly account for enough difference in order to win races but they
won't impress from a marketing point of view. The competition is also
selling improved blades and so, while the difference with old oar
designs might be high, the difference with the competition is possibly
not impressive. Both competitors would sell more if they do not supply
numbers and keep everything uncertain. Possibly because of this, oar
manufactures are not keen on proving by numbers that they are better
even if they are the best. Especially since rowers and coaches alike
are not very bothered with scientifically oriented numbers.
I would agree that a good biomechanical test, in order to improve
rigging, other easily adjustable parameters or assist training
practice, might lead to better improvement of results without even a
need for changing the blade shape or other materials. However, an
elusive fancy blade is much more attractive.
Carl Douglas
To expand on Tinus' very valid observations & Paul's post:
I have seen no evidence for the racing utility of vortex edge blades,
but I am concerned about equipping oar tips with an array of sharp
edges. Further, I learned recently of a collision in which resulting
lacerations to heads needed sutures & raised alarm with staff at the
hospital.
Next, I'd say that before investing in different kit it's worth
exploring better ways to use what you have. Put very simply: can you
change your stroke in such a way that, without reducing the work you do,
you leave smaller puddles?
I ask because we have one easy measure of our rowing stroke's efficiency
(= ratio of propulsive effect to input effort). We call it the puddle.
Each puddle is a roiling pool of entirely wasted energy. As such, it
is the predominant & most visible component of the input energy which
did _not_ move the boat. Reducing its magnitude (hint: row a tad deeper
in the mid-stroke, rather than following the naive orthodox edict to not
loom) is, however, bound to make the stroke feel "heavier". So you'll
have to be prepared to adjust your technique & stroke cycle to
accommodate, but not to destroy, this changed feeling - but do not try
to pull any harder, just allow the extra time in the water.
Further to that, wanting better performance from a blade with no change
in how the stroke is made or feels is like expecting free lunches.
Yes, Tinus is right: rowers & coaches are not very bothered with
science-based numbers. The sport still largely believes that technique
is all about art, style & feel, inaccessible to science - hence the
encouragement in the UK of "British Rowing Style". If this is the
'right' way to do it, where's the deep underlying dynamic analysis &
where are the numbers??" When will the eager proponents of such
orthodoxies twig that fast rowers come in many shapes & sizes & row in
differnt ways? When will they buckle down, instead, to a systematic
analysis of every part of the rowing cycle & the mesh of interacting
effects & consequences within the boat, the crew & the water? When will
the physics of oared propulsion receive one tiny fraction of the
attention paid to style & beating up the water?
Tinus
Getting the shafts around 70 degrees means that there is both an
advantage and disadvantage. If the advantage of 70 degrees can be
taken as a fact then this would mean that it can be considered as an
important aspect and achieving the same effect in other ways may be
worth to strive for.
The disadvantage is that the handle speed is low so the rower can not
apply maximal power easily. Also, large static forces are required
which the rower must be able to sustain. The advantage is that during
a larger part of the stroke propulsion is created by lift forces
(which are more efficient).
Carl Douglas
Which, of course, recognises the progressively varying gearing which is
built into the rowing action - the ends of the arc have the most severe
gearing as well as very possibly the highest propulsive efficiency.
When you are moving fast, it is advantageous to have that longer catch &
with it not just the longer stroke but also the higher overall
efficiency. And that longer catch does not necessarily imply larger
static forces!
Let's examine the loading process at the catch. Due to the flexibility
of the oarshaft, you cannot instantly load your blade:
1. It takes time to build up the load because it takes time to move the
(_lightly_ loaded) handles enough to generate the flexure that give the
load you want to apply.
2. It takes speed of handle movement to significantly exceed the
natural speed of rotation of the handle around the pin, or you'll get no
flex & thus no load.
3. So it takes distance of hand movement to get to your loading.
We make big errors if we try to analyse the rowing stroke without taking
proper account of all of the elastic & dynamic interactions.
So the faster you go, the faster your catch action must be (review the
Ivanov film sequences posted on Youtube by Charles Carroll) just to get
your load on within a reasonable movement. Which again makes it
sensible to use a longer catch _ the harder gearing of that part of the
stroke, far from overloading you, assists the catch-loading process.
I'll make a further point, more relevant to sculling than to sweep:
Consider the resolution, at about your neck, of the force acting at
along the boat into the resulting forces in the arms. If the arms are
out at 30 deg from the boat's axis & the pulling force along the boat's
axis is F, then each arm pulls F/(2 x cos(30)), or about 58% of the
total axial load. If that angle increases to 40 deg, each then pulls
F/(2 x cos(40)), or 65% of the total axial load.
There's a common demand that arms must be kept straight at the catch. I
regard this, as many rowing edicts, as simplistic. It demands you move
the largest part of body mass to initiate a fast-moving, initially
lightly-loaded catch. Yet plainly the fastest, most immediate connection
to the handles under light loads is made by early arm movement. It is
also simplistic not seeing that the load in the arm muscles for a given
pulling load is least in the first few degrees of elbow bend but
increases rapidly as the bend increases - as anyone trying to do that
last, impossible pull-up knows.
So the arms have ample strength & speed to make an early contraction at
the catch. That helps get the hands moving fast enough to well exceed
the free handle movement & get the shaft bending & thus loading early.
Once the bigger forces from the back & legs kick in (it must involve the
back, whatever it does in relation to the legs, since the back is the
sole connection from the legs & must also rotate WRT the descending
thigh - or you get a monstrous bum-shove!), the arms may be drawn
straighter or lock for a while under the increasing load.
Anyway, you see both how rapidly the load on the arms reduces as a
fraction of the axial force at the neck as they swing inwards in
creating the essential initial shaft bend. And that they are perfectly
able to sustain high loadings when not too far from full extension
(remember, what will break your hold on the handles is not a failure in
the arm but loss of your finger grip - which never happens in rowing).
So there seem to be no obvious downsides, in loading terms, to a longer
catch. All you need to justify it is adequate boat speed.
A complex old activity, isn't it? But we do have the mental capacity to
tease out & analyse all the separate but inter-connected threads that
knit together into a rowing stroke model. And thus we can evaluate the
worth of all the popular coaching mantras. As Hercule Poirot said, we
just need to engage the "leetle grey cells".
Walter Martindale
I'm only stating observations from people who were filmed/photographed
while they were/are at the top of the sport.
The most recent is still racing. I'm not really allowed to share too
much of that information
What I've observed also is that most of the movement to load the
blades after they go in seems more like the hands being used to hold
onto the handles while the pins are pushed against the blades by their
connection to the foot-stretcher, than by any effort to pull the
handles in for the purpose of loading the blades. The blades get
loaded because they're connected to the rower who keeps the handles
from being pushed outwards when the foot-stretcher is loaded - causing
the blade end to start pushing sideways on the water, getting that
lift happening as the movement of the boat drives the blade along the
length of the blade. When they're going fast, it ALMOST appears as if
they're shooting the slide/bum-shoving/whatever you call it, but I
believe that the thing they're doing is loading the blades at the
pin.
Another thing Carl mentions is that this long catch stuff works when
the boat's moving. When the boat is still, you need to have a shorter
catch, so that you can start moving the boat by pushing backwards on
the water, more than outwards. If you're trying to use the (formerly
thought to be) most efficient 20 degrees either side of the
perpendicular for any more than the first few strokes, you throw away
all the advantages of the water flow along the blade during a long
first phase of the stroke. Again - more a part of sculling. At a
coaching conference in Vancouver, Volker Nolte described the
similarity of the first phase of a long stroke to the pathway taken by
the pushing blade of a speed skater - all of the force in a speed
skater (after the initial 10 or so strides) is directed sideways - as
much as possible, and when they start getting tired, commentators say
that is looks like they're pushing back (easier, lighter, slower
skating speed) more than it looks like they're pushing out (harder,
heavier pushing, faster skating speed). The longer arc of the long
catch and the first phase of the stroke is one of the reasons that
Kleshnev's "innovative rigging" tends to allow for similar boat speeds
with lighter perceived loading.
Carl is right - it's a bit complicated.
I recall when the world champ lightweight rower who goes/went on this
forum under the name ben - jbrontey (sp?) addressed the Calgary Rowing
Club awards banquet - he named 5 things that were important to be a
world champ rower. One was OCD (do the same thing over and over for
years). One was luck (live somewhere that there's a rowing club, a
good coach, parents who could afford to get you rowing, actually find
out about and try rowing because in my country it's really not
promoted that well...). One was good physiology (choose the right
parents so you are capable of developing a large aerobic capacity), I
forget the next one, but the last characteristic was a long, well-
timed catch.
Walter
ben
> Club awards banquet - he named 5 things that were important to be a
> world champ rower. One was OCD (do the same thing over and over for
> years). One was luck (live somewhere that there's a rowing club, a
> good coach, parents who could afford to get you rowing, actually find
> out about and try rowing because in my country it's really not
> promoted that well...). One was good physiology (choose the right
> parents so you are capable of developing a large aerobic capacity), I
> forget the next one, but the last characteristic was a long, well-
> timed catch.
>
> Walter
Spare time.
Cheers.
Ben
PS I'm back in Calgary Walter getting ready for the master's 8+ at
Charles. We have a bunch of just-under-40's and our old coach to
bring up the average. Was also in NZ for a week or so last month
(funeral) and saw Karapiro. What an incredible facility.
Walter Martindale
Wish I'd been there to see you but I'm in Canuck land.
W
StephenA
Hi all,
the Computational fluid dynamics (CFD) guys have been trying to
understand the fluid dynamics of the blade. Capan (Birmingham Univ)
and more recently Sliasas (McMaster Canada) have produced papers - you
may be able to access via Google Scholar. When comparing with
aerofoils which usually have high aspect ratios (Length to chord
length) e.g. wings and sails, the rowing blade has a very low aspect
ratio (< 0.5) and so water doesn't only flow along the foil but over
the top and bottom. This means that the stall angle of attack is about
45 degrees not 15 degrees as in most aerofoils. They calculate both
lift and drag in their models but don't have the right answer yet.
But reading their papers helps a bit.
Stephen Aitken
Carl Douglas
Makes sense that the oar blade, as a low aspect ratio foil, should show
some of the characteristics of a delta wing.
A blade known as the Feathor was a lot more like a delta, & didn't
perform too badly either, considering its much reduced area. Ditto the
Alden Deltor.
manofoar
<snipped to shorten the post>
> If you go to this forum, you’ll see that I have tried, to the limit of
> my understanding, to explain lift to Caustic.http://www.rowingillustrated.com/boards/viewtopic.php?f=16&p=49432#p4...
> You may also note my impatience and decision to abandon the effort.
> Carl and others may recall that some years ago when I was having some
> difficulty understanding the concept of lift, I asked questions on
> RSR. Anyway, I hope in my remarks the student did well by my
> teachers.
>
> Steven M-M
Really? I don't actually see you mentioning any kind of detail on
lift, other than saying that I was wrong, and that you knew better.
This isn't 16th Century England, where Lord Boyle can drum out folks
out because he doesn't like their idea of attacking his heat theory.
If you don't understand this hypothesis well enough to clearly explain
it to even ME (I would say 8 year old, but I already know you folks
think an 8 year old is smarter than me), can you really say you
understand it?
Show me the data, in short. This is what I love about lift
proponents. They have a post-hoc fallacious understanding of rowing.
Hey! there's some lift on the blade! OBVIOUSLY is must be doing
something important! I may not understand lift, but I do know
bullshit when I see it, and any kind of scientific background has one
common thing: experimentation and repeatability.
However, unlike real scientific research here's what this lift
hypothesis is lacking:
1)Real numbers from dynamic, numerical measurement. Not taking
discrete angles and waiting for a steady-state flow to be established
before measuring lift - this situation doesn't exist in the real
world. Using numbers from this wrong king of experimentation are not
applicable to a real rowing stroke.
2)An accurate dynamic model - showing the flow around the blade with
an accurate rendition. Not just estimating, but being able to take an
animated model, and see a direct commonality with a real rowing
stroke.
Caustic
manofoar
see the same flies are still buzzing about. >:)
On Aug 25, 5:49 am, Carl Douglas <c...@carldouglas.co.uk> wrote:
<snipped for brevity>
> Ian, you're a terrible old stirrer. Fancy winding up the good &
> sensible folk of RSR in that way! Shall we apply the acid test: add
> some acidic HCl to neutralise silly old Caustic's NaOH & turn him into
> salt .
>
> His intention & lack of grasp is apparent throughout. But he doesn't
> want understanding, just to bludgeon folk into his blind followers. If
> you don't understand fluid dynamics it is easy to create bogus arguments
> against its established facts - provided your audience also lacks those
> same insights. Much of what fluid dynmaics tells us is very
> counter-intuitive, making it that much easier for the obscurantist to
> gull a captive audience. How sad!
Well, good to see you got the ad hominems out of the way right off the
bat. Let's continue! :)
> His ramblings are so mad it's hard to know where to start. A flying
> brick _does_ produce aerodynamic lift, but he doesn't see that lift may
> not work in one direction only, nor against gravity. He doesn't see
> that if the mass is high, the area for lift generation small & of highly
> non-aerodynamic shape (e.g. a brick!), & the working fluid of low
> density (air), then lift forces, although present, will have little
> influence. Some fighter planes were said to have the aerodynamics of a
> brick, but they did have wings. The wings, not found on bricks or pigs,
> provided the lift to keep a hefty plane aloft while huge engines
> overcame the aerodynamic drag. No glider (which, like bricks, lack
> engines) resembles a brick.
>
This is where you geriatric mind starts to wander, Carl! I actually
never said that a brick doesn't create lift. I said that it doesn't
create APPRECIABLE lift. I.e. enough to significantly change it's
distance from a purely ballistic projection. I purely understand the
whole interrelation of mass to surface area and medium travelled, and
one more - DIRECTION travelled with relation to lift force. I.e. any
lift vector will be at 90 degrees to the velocity vector. Think about
that for a moment. It's ok, I'll wait.
> I should add that, because drag on a brick doubtless exceeds any lift (&
> a brick's lift will oscillate between up, down & sideways) it _will_ go
> further if thrown in a vacuum. So he's comprehensively wrong. Let's
> hope old NaOH never flies anywhere: if he's right, planes won't fly, or
> if airborne must crash.
Yes, it will travel further in a vacuum - but due less to lift
"oscillating", and more due to a lack of friction - i.e. DRAG.
> Next, his snide insult to oarmakers. I might think oars are not yet of
> perfect design, but they ain't bad. This guy doesn't even understand
> that oars don't "push" water - even though it's so easy, even from
> visual evidence, to show how little & insufficient pressure there is on
> the face of a working blade.
Hatchet designs have existed for over 80 years. Only 30 years ago did
they get very popular, for two reasons:
1)Modern composites ensure that they wouldn't break of split along
wood grains
2)Oarmakers started talking drivel, not substantiated by any 3rd party
confirming research, that it was LIFT that made them better.
Folks knew back in the 50s that *if* you could get a hatchet oar
strong enough, it would move the boat better - also assuming that the
rower's backs didn't give out because of the heavier load. Hatchets
are not some strangely revolutionary design in rowing - folks have
known for a long time that if they could get more blade underwater
without having to stick more shaft underwater to do it, it could make
rowing faster easier, because it cut down on DRAG.
> Oarmakers must know that their public, led by the spoutings of such as
> NaOH, haven't a clue how oars work. People favour bigger blades becasue
> a bigger bat has more drag than a smaller one in the stalled mid-stroke
> phase. They want more area because such as Caustic tell them the
> mid-stroke is the best, most efficient place to pull.
You see, Carl, you like to imagine that I say some things, and
unfortunately, I didn't say this. Citation please - Again, I never
said that the mid point of the place was the most efficient place to
pull. It's where the greatest slip is, I'll definitely agree. As for
when the boat's accelerated the most for amount of work, well,
mechanically, this is the most efficient leverage to move the boat.
Even you have to agree that, in terms of leverage, this is the case.
If I was a crew at a racing start, I start my blades at 1/2 stroke,
not at full stroke. Why? Because if I want to move the boat from a
point of rest as fast as possible, I do it where I have the greatest
mechanical ability to do so - every ounce of weight I put on the oar,
at rest, at 1/2 stroke, is most optimally put towards moving the boat,
because the force vector is facing directly towards the stern. that's
just the law of the lever and good ol' Newton working there.
But strangely enough, the best place to start the race is where the
least amount of lift is. Hmmmm. Yet we use blades "designed" for
"optimal" lift.
>That's pure Snake
> Oil, there's no evidence for that claim, but evidence rarely concerns
> snake oil salesmen. Oarmakers will offer the bigger blades the public
> think they need, or lose business to those who do. However, thanks to
> discussions long ago here on RSR, few oarmakers have zero grasp of the
> relevance of hydrodynamic lift to oared propulsion. Never mind some now
> irrelevant face features (spines, etc.), for centuries sweep oars &
> sculls have been curved both ways over their back faces for very good
> hydrodynamic reasons. Similarly, lugging oars are straight & have an
> elongated diamond or elliptical section for similarly good lift-related
> reasons. And those different shapes relate directly to the differences
> in how they're used.
Ah yes! Try not to pat yourself on the back too hard Carl. And since
you seem to have a selective view of history, perhaps you don't recall
the fact that after the Hatchet came the Smoothie, then the Big Blade
Smoothie, then the "Vortex" stuff from C2, etc. etc. - all within a
very short timeframe once the whole lift boondoggle caught the eye of
coaches looking to buy new equipment. Toss in a couple "whitepapers"
with some cool animations, and voila! The lift 'theory' is born and
the rowing world is a kinder, gentler place for it.
Too bad reality isn't like that.
> Too much of what NaOH rabbits on about is mere bombast & best passed
> over. He fails to understand either the velocities, the forces or the
> flows over a blade, though a bit of Googling could have spared his
> blushes. But his closing swipe vividly displays his inept logic: he
> falsely asserts something as both fact & precedent without a scrap of
> evidence, then claims this proves hydrodynamic lift is a fantasy.
On the contrary! I have seen a lot of the research on blade lift that
uses static angles to measure lift. Sure, in a STATIC scenario, lift
is generated that is distinctly measurable. But for dynamic scenarios,
where they try to measure lift through a continually changing angle of
attack? Lift is significantly degraded, as the more modern (and less
common, because it so much harder to measure or computationally
calculate) shows. I linked to an abstract in the post I had on
RowingIllustrated. Previously, there was another study someone linked
to that also showed that the lifting force on the blade was not
contributory towards propulsion in any meaningful manner.
This is where we realize that just because you can model something
nice and pretty, the simple fact is that does not logically conclude
that reality must be so simple and pretty. And you can't even create
an animated model with that static research, so how can you move to
designing a blade when you can't even model it? That's called "trial
and error", not "research".
> When absolutely static there is no forward motion, so there can't yet be
> flow along the blade. The fluid drag initially generated by the
> slightly moving loaded blade is, of course, the first force to give a
> forward impetus. But the boat accelerates, & as it does so a triangle
> of velocities is established: movement of blade about pin & movement of
> pin across the water establishing a resultant water flow from tip to
> root of blade. That flow is all it takes for lift to be generated (over
> the back of the blade) & to displace drag as the prime force acting on
> the blade.
Wow. It's like you don't even look at the rowing stroke before you
draw your conclusions.
Here's a similar situation - take your arm, and use your hand as the
blade, and swing from catch to finish in the water. As you swing
around the stroke, do you feel the water pulling along the back of
your hand, or do you feel it pushing against your palm? Lift is,
ultimately, a low pressure area pulling the object into the low
pressure area - not pushing it. If you feel the water pushing against
your hand, that's by default NOT lift.
But the problem is this - that is not at all what is happening to an
oar. It is very easy to see that we have water spilling over the top,
spilling up fro the bottom, and spilling around the tip and root. All
that water moving in 4 different directions, interfering with each
other, and not to mention the fact that the pocket forming is
deforming our medium even more. When you have 4 different flows
colliding in the middle of the blade, you don't get lift. You get a
whole lot of turbulence, and turbulance doesn't generate more lift
than drag.
Before you disagree, this is very easily verifiable. If you've got a
dockbox, you can do it, or just take a look at someone's blade when
they do a catch or finish drill - you will see the counter-rotating
vortices at the tip and root. This is nowhere near the stall phase.
Then you approach mid-stroke where stall kills lift, at
> which point (if you understand what's happening) you'll bury deeper to
> prevent aeration from breaking the important tensile connection between
> the back of the blade & the water. And as you approach the finish,
> already a good way towards eventual cruising speed, lift re-establishes
> itself as the main force resisting the load you put on the blade.
You know, this actually brings to light another big hole in the lift
theory - it assumes that the water the blade is encountering is not
being displaced. An airplane wing in flight mode contributes
essentially zero net displacement to the air it passes through - it
flows up and over the wing, but back to nearly its original location
once the wing passes by. Part of the fundamental tenets of lift as a
force acting on an object is that the net work done to the medium the
object is passing through must be zero. I.e. all the work done is on
the object moving through it.
This is not the case with a rowing stroke. you can easily see that a
LOT of
> But NaOH claims that the first instant of the first stroke is typical of
> the rest. Even the Red Queen would think that irrational.
>
> Cheers -
> Carl
Not that it's typical - but that it's operating OUTSIDE of the lift
theory. Part of having a complete "theory" is in making it actually
complete - not just covering the parts you want.The fact that I can
have any catch, of any stroke, and not have lift in it means that your
theory of lift being a PRIMARY force is highly suspect. In the
scientific world, if I had said that all the planets operate like
thus, but someone finds an exception, that means that my theory is
quite likely flawed, and more possibly not even accurate. For example,
think of Ptolemy and his description of the planets - while it
provided applicable uses (i.e. they could determine time of the year,
navigate, etc), it was actually fundamentally flawed in what reality
was doing.
This is much like hte theory of lift in rowing - because annoying
"facts" like the mass of the water actually moving, and that the
vortices don't form when you want them to, but when they actually do,
your very trite and clean idea of rowing is, in fact, not at all in
line with the real world. You can sometimes draw some interesting
applications, but that does not mean that it is actually correct.
One of the very first concepts that I learned in college, way back
when, was the Principle of Universality. I.e. that the forces and
fundamental rules of causality are universal. If we can find some sort
of scenario by which we can show a LACK of this universality, it does
not mean that the universe is wrong, but that the hypothesis is wrong.
The first stroke is an extreme example, but models are tested by how
they respond to extreme conditions, not ideal ones. In this case, the
lift hypothesis easily breaks down. If lift were truly the primary
means of moving a boat by anchoring the blade, we would not encounter
the INSTANTANEOUS resistance to pulling like we do IN REALITY. If lift
were the primary means of moving, the heaviest weight felt during hte
stroke would be when the lifting force was at a maximum - when edge-on
velocity vector is maximal as the blade rotates about the pin. But in
reality, this is NOT the maximal weight felt by the rower. The rower
feels the greatest weight well before that.
I'll head back to RowingIllustrated - the garbage is still fetid here.
Caustic.
mruscoe
> Hatchet designs have existed for over 80 years. Only 30 years ago did
> they get very popular, for two reasons:
20 years ago.
> 1)Modern composites ensure that they wouldn't break of split along
> wood grains
> 2)Oarmakers started talking drivel, not substantiated by any 3rd party
> confirming research, that it was LIFT that made them better.
>
> Folks knew back in the 50s that *if* you could get a hatchet oar
> strong enough, it would move the boat better - also assuming that the
> rower's backs didn't give out because of the heavier load. Hatchets
> are not some strangely revolutionary design in rowing - folks have
> known for a long time that if they could get more blade underwater
> without having to stick more shaft underwater to do it, it could make
> rowing faster easier, because it cut down on DRAG.
Bigger area, more drag. Surely.
manofoar
> We might, Steven, have to mark you down just a point for that early
> remark you made there on lift, hinting at a possibility at the catch of:
> "maybe some positive pull towards the finish".
That was the opening, of course.
> Trolls hide under bridges, just waiting for slips such as that
> unfortunate addition to your sentence. No matter.
Amazing how those with few facts are quick to attack those with
slightly more.
> As another poster says, the photo NaOH introduced shows only a blade at
> mid-stroke. Hence no flow along, & lots across. (And it's too shallow,
> with a stupid great hole behind it).
No matter how deep you dig, unless you're dredging the bottom of
Thames the water will still flow around all 4 edges the same way. I
can do that at the catch, at the finish, at any angle you want and get
it to do that. That pocket doesn't form at the stall, but much
earlier. So, that's more of the stroke stubbornly defying your
dogmatic view of "lift" being primary. Stupid reality! Can't it know
it will never defeat the Great Carl Douglas!?
> NaOH evidently can't deal with moving objects & velocity triangles.
> Must've hated maths lessons & dreaded simple geometry. But he had twin
> gifts: he could ignore facts & logic & could browbeat all comers.
Oh, I'm great with triangles and moving objects. But you seem to
forget about stupid things like the fact that water is liquid, and
that when you push against it, it flows AROUND stuff. And you keep
forgetting that the blade is travelling in more than one direction -
so a wing like a plane is actually a horrible comparison, because the
plane will be flying straight and level when lift is most efficient.
The oar never does this.
You keep thinking that the blade is traveling some perfect
mathematical arc, when it's not. you assume that it's not slipping
when you don't want it to (further distending this arc into something
much less mathematically pure), you assume that the water is flowing
the way that ensures maximal lift. you assume, and assume, and assume.
In reality, these assumptions are false. Water flows around all 4
edges, the blade slips, the arc it transcribes is very mathematically
awkward to model (because of the density of water and how it allows
the blade to slip through the stroke), and also all that damn
turbulence, which adds drag and reduces the surface of the blade able
to provide lift - and that silly pocket when you believe shouldn't
exist (but it does, and people win races with it there).
I think it is much more apparent and logical to very clearly see that
a very large mass of water is affected by the blade due to the stroke,
and that it would be very logical and easily verifiable to account for
that volume of water, it's average velocity, and the density and thus
mass. When you dig
> He takes "lift" to be a free energy source (like a perpetual motion
> machine), not a natural process in which a fluid's internal pressure
> falls as its flow bends around a convex surface. And he proposes that
> the lift process, known to every student of fluid dynamics, exerts a
> magical pull all of its own. (Perhaps you suckered him in?) Then he
> shows this can't be so, & makes the illogical deduction that lift (&
> history too?) is bunk. That's how Stalin dealt with those he disliked -
> accuse them of impossible crimes, then kill, imprison or exile them
Ohh! I wonder if we can add on a corrolary to Godwin's Law, since you
threw out Stalin instead of the more hum-drum Hitler reference.
Uh, now this is where you break from assumption, and start running
straight into pure fantasy.
1)I never said or implied that lift is free energy
2)I never said or implied that lift exerts some "magic" pull
I really don't know how I can defend myself against statements that I
never said.
Here's what I said - lift is not a primary or even largely
contributory force for moving the boat. Why? Because the conditions
for that amount of lift just plain don't exist around a real oar in a
real stroke.
Here's what you are all assuming
1)The oar is moving forward at the catch, in the water. This is not
happening in reality, unless you want your boat to promptly not move
forward anymore. When it enters the water, it will be at rest with
relation to the water. It cannot be moving forward and propelling the
boat at the same time.
2)You need the oar to assume some constant lift in zero time, maintain
that lift for a time, and then loses that lift in zero time again at
the stall. Repeat process during the back half of the stroke. First
rule of physics - sharp corners on velocity/time plots mean that the
universe is not being observed correctly
3)You assume that any time the boat is moving, lift is moving it. See
#2.
More tellingly, your own ignorance is starting to show. Not too much
fun finding out the emporer has no clothes on!
> NaOH tells lies about established science, then accuses knowledgeable
> people of telling lies. That's shameless demagoguery of the worst sort,
> but relatively harmless provided he a) stays out of politics & b)
> doesn't do it in the street & frighten the horses.
>
> Rowing could use fewer such nutters.
>
> Cheers -
> Carl
"established science"? I'm sorry, I'm not sure what you're talking
about there. There's actually science going on with rowing strokes?
Last I saw, there's a bunch of people dreaming up ideal situations and
then fallaciously saying that reality is conforming.
Strange that you don't see too much peer-reviewed publications on your
side either. But we should all just be quiet and buy what we're being
sold, eh?
Caustic
Chris Kerr
> On Aug 25, 11:09 pm, Carl Douglas <c...@carldouglas.co.uk> wrote:
>
>
> Here's what you are all assuming
>
> 1)The oar is moving forward at the catch, in the water. This is not
> happening in reality, unless you want your boat to promptly not move
> forward anymore. When it enters the water, it will be at rest with
> relation to the water. It cannot be moving forward and propelling
the
> boat at the same time.
> 2)You need the oar to assume some constant lift in zero time,
maintain
> that lift for a time, and then loses that lift in zero time again at
> the stall. Repeat process during the back half of the stroke. First
> rule of physics - sharp corners on velocity/time plots mean that the
> universe is not being observed correctly
> 3)You assume that any time the boat is moving, lift is moving it.
See
> #2.
>
>
> Caustic
I'm not an expert on fluid dynamics, so I won't comment on the
theoretical discussions. However, I have spent a substantial amount of
time watching oars as they move through the rowing stroke, and in my
experience the oar does indeed move forwards (i.e. towards the finish
line) relative to the water during at least the first part of the
stroke. (It moves backwards relative to the boat, of course, but less
quickly than the boat is moving through the water.)
This is more obvious in sculling than sweep, as the catch angle is
higher, but the effect exists in both disciplines when rowing full
slide. Indeed, when sculling, the forwards-through-the-water motion in
the first part of the stroke often outweighs the backwards 'slip'
during the rest of the stroke so the tip of the oar comes out of the
water closer to the destination than it went in.
Carl Douglas
> ooooh! It's rare that I visit here nowadays; been a long time, and I
> see the same flies are still buzzing about. >:)
>
You'd not get treated as foolish if you were prepared to enter into a
reasoned debate. You throw unsolicited insults. You jump to unfounded
conclusions. Your logic is seriously deficient. Your arguments are
technically illiterate. You coarsely impugn the motives of those you
think are wrong. It is like watching a bull in a china shop.
>
>
> I'll head back to RowingIllustrated - the garbage is still fetid here.
>
>
Fine by me, & maybe fine by others too, since you appear intent on
tarring all of RSR with the same brush. But why write those 3
inflammatory posts to RSR before leaving? It doesn't impress, it just
leaves a foul taste. Do they enjoy your petulant, irrational tantrums
better on RowingIllustrated, or do folk there just roll their eyes &
look the other way when you shoot from the lip?
What some of us are trying to do in these discussions is to apply the
science of fluid dynamics to a sport which for too long has been
determined to ignore it. In the process we hope to identify and clear
up genuine misunderstandings, & of course we also hope to learn. If you
can debate at that level, please join in. Just don't expect us to
listen if you shout & insult.
>
> Caustic.
It's not very brave or smart to be so caustic & abrasive while hiding
behind a pseudonym. If what you say might embarrass or expose you in
real life, why say it at all?
Phil
> > Caustic.
>
> It's not very brave or smart to be so caustic & abrasive while hiding
> behind a pseudonym. If what you say might embarrass or expose you in
> real life, why say it at all?
>
Carl - you should know the interweb isn't anonymous, as should :
http://www.linkedin.com/pub/edmund-joseph-tynan/a/b38/257
Phil.
Carl Douglas
Phil, that's very interesting. I bow in amazement to your vastly
superior knowledge of such things! I won't even pretend to guess how
you can do that.
I do understand that, if a coach has been instructing his/her charges
along a particular long-held set of beliefs & understandings, it can be
tough, even embarrassing, to be confronted with views which conflict
with those they normally promote.
Coaching is a tough job, & actual understanding of the rowing stroke is
not broadly relevant to getting a crew together & getting early results
- togetherness matters a lot more than anything else. And as long as
every coach accepts that certain aspects of boat propulsion are
inaccessible to science, why open that particular can of worms? In that
context, smart-arses introducing knotty concepts from a field of
learning which isn't exactly your own can be pretty darned irritating.
It all depends on the sort of guy you are. Some like to shun areas they
don't understand & to publicly dismiss them as obviously irrelevant - it
seems to preserve face & drive out the purveyors of anathema with blasts
of derision. Others accept, even welcome, the challenge of learning
from insights & knowledge of others. I think Mr. Tynan, if that be he,
is of the former persuasion.
I see that fluid dynamics is not one of his stated specialities. And
I'm assuming that Caustic doesn't write in The Spectator in similarly
inflammatory terms?
Walter Martindale
>
> Here's what you are all assuming
>
> 1)The oar is moving forward at the catch, in the water. This is not
> happening in reality, unless you want your boat to promptly not move
> forward anymore. When it enters the water, it will be at rest with
> relation to the water. It cannot be moving forward and propelling the
> boat at the same time.
>
> Caustic
Ok, "Joe"... I'd suggest that you take a good video camera to a high
bridge under which an accomplished (male for longer stroke length)
sculler trains, and film - note the catch angle of the blades, and
note (if the water is at all clear enough) how the blade tracks in the
water after the entry. Do this frame by frame. Do it with a "let's
see what happens" attitude instead of "I know what happens and want to
prove it."
I asked a guy who was doing fluid dynamics research once if he knew of
a way to actually measure what's going on during a rowing or sculling
stroke - he thought about it for a few days and came back to me and
said that it was too complicated for him - he was only doing a PhD...
So - just how DO you do studies on lift (presence or absence) in the
live situation of a rowing or sculling oar? Where do you put the
strain gauges? How do you measure the pressure on the front and back
faces of the oar in real time in a real sculling stroke?
Walter
Walter Martindale
Further to the above - Have someone row through Montlake Cut - there's
a really good bridge there. Stationary camera pointing straight down
so you're not tracking.
W
Charles Carroll
Have you ever given any thought to the idea that maybe your arguments
would be more creditable if you just didn't make everything personal?
Cordially,
Charles
Carl Douglas
>> You should consider lift forces due to horizontal motion of the blade
>> instead of vertical motion. Lift forces analogue to the lift forces
>> with sailing.- Hide quoted text -
>
> I understand that in rowing we are talking about the horizontal motion
> of the blade in the water generating lift forces that have a forward
> element, unlike kayaking where vertical movements generate forward
> forces. However I still need enlightening!
Some clarification, I hope:
In canoeing (single paddle) the vertical stroke entry with a forward
raked blade generates lift.
In kayaking (double paddle) both vertical (entry) & lateral (the stroke)
movements generate lift.
For those unfamiliar with the "wing" paddles used by racing kayakers,
these have blades of relatively complex shape which on any cross-section
resemble conventional aerofoils that were made hollow & had their
'lower' faces cut away (a terrible piece of ASCII-art follows):
_ _ _
_ - - " -
_ - \ ----> direction of motion during stroke
paddle blade _ /
The kayaker, after entry, drives the blade largely sideways out frm the
boat, with the paddle's convex surface facing approximately forwards.
Lift generated across the convex surface by this motion counterbalances
a static sternwards pull from the paddler (lift always = load) to propel
the boat. And the paddle blade exits either in transverse line from
where the side-movement began or, often, ahead of that line.
Paul
As the captain of a fairly small club which cannot afford to change
blades every time a new 'improvement' comes along it would be nice to
get some clear guidance from those more knowledgeable than myself on
which are the best blades to buy. It does not help that blade
manufacturers choose either to give no data or provide only limited
data which is accompanied by a caveat saying that different blades
will suit different rowers! In the end it all seems like opinion as
there is little data available. I guess we will just buy what we have
always bought for the last few years.
Paul
Carl Douglas
Paul - I don't think that, as a sculler, or as a rower, you're going to
be using wing paddles ;)
I'm not here to advise on which blade anyone should use, & hold no brief
for any particular make. But how do you reach whatever conclusion you
do reach on a choice of blades? Do you decide on feel, & would feel be
a valid indicator? Do you play with your technique, doing time trials
with different blades until you find a combination of blade & technique
that goes best? Does feel matter most of all, whether or not that goes
with performance?
A tough one. And it might be that the differences between them are too
small to matter - does that mean they're all right, or all the same
amount wrong?
Greg Doyle
> Well as my dad would say - this is as clear as mud.
>
> As the captain of a fairly small club which cannot afford to change
> blades every time a new 'improvement' comes along
You don't need to do this. Most improvements are just
that...improvements, like an optometrist's A vs. B adjustment to your
testing goggles. Minor adjustments don't render older designs unusable
with the existing equipment and styles rowing. When you get something
that requires a fundamental shift in the way you do things, then
you'll want to investigate, out of curiousity rather than compulsion
hopefully. You might like, you might not.
>it would be nice to
> get some clear guidance from those more knowledgeable than myself on
> which are the best blades to buy.
There is no one more knowledgeable than yourself in terms of which
blades you should try and buy. Asking someone else to provide some
sort of cheat sheet would rob you of the very interactive element that
defines our sport. Your connection to the water is a subjective one.
Your choice of equipment should be similarly founded. When a machine
does the rowing, then a machine can compare the oars in a sterile
setting. Until then, you are the more important part of the equation,
and you should not underestimate your sense of comfort in the calculus
of rowing propulsion.
>It does not help that blade
> manufacturers choose either to give no data or provide only limited
> data which is accompanied by a caveat saying that different blades
> will suit different rowers!
Then you're in the wrong sport, friend. Designs often evolve for
intuitive reasons more than scientific ones. If you think boats are
any different, you're fooling yourself. Science is "borrowed" to
spackle, but it does not seal or encapsulate the presentation. If you
don't look at a rigged boat with oars and see a Rube Goldberg
contraption screaming at you, then we must be seeing very different
things. Over 25 years, I have come to enjoy that as the beauty of our
sport, matched only by the bizarre anatomical manipulations often
undertaken by the human sitting atop it.
> In the end it all seems like opinion as
> there is little data available.
Yes. And what data exists often measures relatively simplistic
things....deflection under load. Is that really the sum total of an
oar or boat's value? Seems to be missing quite a bit, yet many
manufacturers trot it out for the crowd.
>I guess we will just buy what we have
> always bought for the last few years.
Hmmm....then you shall get what you always have gotten, correct? That
could be good, or bad. Rowers need not fear experimentation. In team
boats, you might want homogeneous rigging, but there's no law that
says the brands need to match. I'd rather see four happy scullers in a
quad each rowing the oars they love. Better yet if they swap
occasionally.
Paul
If I was buying for myself then I would want to trial as many
different types of blades as I could. Over the years I have sculled
with many makes of blades and have settled for one type for several
years, they seem to suit my less than perfect ‘style’. I am talking
here about buying blades for a club, blades that will be used for many
years and will be used with crews of different abilities and styles.
Some manufacturers claim differences in boat speed of greater than 1%
between blade types, which is huge. Obviously I want to give our
rowers the best equipment we can afford, am I to believe what
manufacturers say or is it just sales spin? Given the lack of data and
the vehement disagreement here about the value of lift, never mind how
different blade modification change that lift I get the feeling its
all spin. Given that we will probably continue to buy the make and
type we have for several years (especially as I like them).
Paul
Phil
I don't have to remind anyone that buying club blades is also more
about what spares you already have (including unbroken bow/stroke side
orphans!), durability, compatibility etc etc etc...
Greg Doyle
> Greg
>
> If I was buying for myself then I would want to trial as many
> different types of blades as I could. Over the years I have sculled
> with many makes of blades and have settled for one type for several
> years, they seem to suit my less than perfect ‘style’.
Good...an openness and a defined preference need not be exclusive
states of mind.
> I am talking
> here about buying blades for a club, blades that will be used for many
> years and will be used with crews of different abilities and styles.
The need for durability seems hand in hand with rowability/raceability
then. Given that the oars will have to accommodate so many different
rowers and conditions, I would suspect the flavor you might choose
would not be so exquisitely unique. You're right, you can't chase the
latest fad. Use the past as a guide and extrapolate into the near
future. Choose the standard "average" shape on the oar you can most
afford to maintain.
> Some manufacturers claim differences in boat speed of greater than 1%
> between blade types, which is huge.
And using transitive logic, some shapes on the extreme end of those
comparisons must clearly be 7-10% faster than those on the other end.
Does that reconcile with your experience? With each design rigged
properly, can an oar make 30-40 seconds difference over 2000m? If so,
indeed that is a major improvement. Let me know where I may find
these.... ;)
>Obviously I want to give our
> rowers the best equipment we can afford, am I to believe what
> manufacturers say or is it just sales spin?
Believe how they make the oars, believe how passionate they are,
believe how they have performed in thousands of races by other people.
Hard part is relating that completely to you or your rowers. Some
aspects will be valid for consideration, others not.
> Given the lack of data and
> the vehement disagreement here about the value of lift, never mind how
> different blade modification change that lift I get the feeling its
> all spin.
Spin is for ergs... ;) or puddles, and Carl's not fond of those....
> Given that we will probably continue to buy the make and
> type we have for several years (especially as I like them).
Probably wise. And if you feel the urge, keep any experimentation on
the conservative side. Compare "like" to "like" in terms of the design
parameters. Too hard to sort out a triangle shaped blade vs. a clover-
leaf shaped blade vs. a star shaped blade. You'd never know what was
making the difference, or if something in between would be better.
Greg
MagnusBurbanks
new thread just posted re CFD modelling of an oarblade does bear out
Tinus, Carl and Walter. Also Carl's views about blade depth too, for
that matter.
Magnus
Paul
It seems to suggest that lift does not reach its maximal effect until
within 20 degrees of the blade being perpendicular to the boat, with
very little lift in the first 10 degrees of the blade arc and
virtually nothing after the perpendicular. It also suggests that
propulsive efficiency does not change as much as I had expected from
the discussion here.
Maybe I have got the wrong end of the stick, this sort of thing is not
exactly my area of expertise, but as far as I can see this paper is
saying some different things. Most importantly, I'm not sure it will
help me go any faster!
Paul
Tinus
The conclusion is that blade shape has a strong effect. So, I don't
see how it doesn't.
You should take a look at figures 5.6 and 5.7 and be amazed. The big
blade has higher lift forces, the macon blade had higher drag forces.
Drag force is parallel to the blade velocity and is the component of
blade force which involves application of work, or mechanical energy
loss, to the water.
Tinus
About the same graphs. Blade force of the order of 2000N seems rather
high. Anyone have an idea what this means?
Carl Douglas
All eight rowers pulling on the same blade?
C
Paul
We seem to be talking about different papers! I was talking about
Sliasas and Tullis 2010. Caplan & Gardner 2010 is very interesting as
it suggests big blades are not very good at creating lift and they
conclude there are significant improvements in blade design still to
be made. I am sure C2 would say they have made them.
Paul
MagnusBurbanks
and I was referring to http://etheses.bham.ac.uk/793/1/Coppell10PhD.pdf
which is the topic of a more recent thread
M
Richard du P
wrote:
> On Sep 3, 12:35 pm, Paul <pgosl...@hotmail.co.uk> wrote:
> > We seem to be talking about different papers! I was talking about
> > Sliasas and Tullis 2010. Caplan & Gardner 2010 is very interesting as
> > it suggests big blades are not very good at creating lift and they
> > conclude there are significant improvements in blade design still to
> > be made. I am sure C2 would say they have made them.
> > Paul
> which is the topic of a more recent thread
> M
Is this area ready for a "Meta-study" [I think it's called?]?!
I promise to read that when it appears; don't want to spoil my
pleasure by reading the separate studies first.
Obviously I'm hoping still to be among you young people, when it is
conclusively proved that Toothpicks Are Best
Richard du P
Carl Douglas
> On Sep 3, 12:35 pm, Paul<pgosl...@hotmail.co.uk> wrote:
>> Tinus
>>
>> We seem to be talking about different papers! I was talking about
>> it suggests big blades are not very good at creating lift and they
>> conclude there are significant improvements in blade design still to
>> be made. I am sure C2 would say they have made them.
>>
>> Paul
>
>
> and I was referring to http://etheses.bham.ac.uk/793/1/Coppell10PhD.pdf
> which is the topic of a more recent thread
>
> M
Ms Coppell's thesis does, I think, represent a very detailed & competent
study. There is a lot to read & I lack time to read it as deeply as it
merits, but my early impression is that it is well done, well written
and well presented.
Had our erstwhile friend, the Man-of-soda, taken the trouble to read it
he might by now be rather less sure of the wisdom of his recent
pronouncements.
Here's hoping, but not holding my breath -
zeke_hoskin
discussion:
Oars are complicated, and attempts to simplify them can be
misleading. At midstroke they behave like a stalled wing, simply
pushing at the water.
At significant angles from midstroke, water is flowing along them and
they are loaded, by the rower, with a force that is perpendicular to
the blade.
Now: when an airfoil is moving through a fluid and there is a force
perpendicular to the direction of that motion, that force is called
"lift". No understanding of fluid dynamics is required to determine
that lift occurs. If you pull on the oars, and the boat is moving, and
the oars aren't perpendicular to the boat, then lift is occurring.
It's not magic. It's just what the word means.
Now, understanding how MUCH lift you get, vs drag -- i.e., how much of
your work is going to move the boat vs how much of it is sloshing
water around -- is exceedingly complicated. I would expect that a
blade shaped like a chunk of airplane wing, fixed perpendicular to the
shaft of the oar, would have considerably better lift/drag. It would
be a very finicky job to get it into and out of the water, and it
would produce a lot of axial torque which would require a positive
stop in the oarlock. Since such a design would be completely legal,
and yet nobody has built one and conquered the world, I can conclude
with a fair degree of confidence that oars don't work much like
propellers.
I'm not going to try to explain how they do work. I dropped out of
fluid dynamics with an honours undergraduate degree.//Zeke Hoskin
Tinus
> Since such a design would be completely legal,
> with a fair degree of confidence that oars don't work much like
> propellers.
The fact alone that oars are not used like propellers does not
logically lead to the conclusion that they don't work like propellers.
As Andrew Sliasas and Stephen Tullis conclude in a recent paper
(http://www.google.nl#q=The+dynamic+flow+behaviour+of+an+oar+blade+in
+motion+using+a+hydrodynamics-based+shell-velocity-coupled+model+of+a
+rowing+stroke) that possible hydrodynamic improvements are not
without additional problems.
"Changes in blade shape ultimately leading to faster crews cannot,
however, occur in isolation. An improved blade design must also be
congruent with existing rowing technique, such that rowers can easily
adapt to its introduction. Likewise, changes in the rowing stroke must
also be acceptable, given the rowing blade being used. The
collaboration between those designing rowing blades and those using
them, then, will certainly result in faster crews."
I believe it is only a matter of time before increasing performance by
other means becomes economically less favourable (because of the
principle of diminishing return) and changes to oar/blade shapes will
occur.
Carl Douglas
I completely agree with Tinus, save only that we should not be so
doubtful of human ingenuity. I'm sure we can design better kit. My
greater concern is the faith in some circles that just by training
people ever harder we can go ever faster - which marries the poisonous
temptation to enhance human power by chemical means with increasing
injury/dropout rates among those who don't cheat.
Zeke jumps from a commendable summary to what I think is an irrational &
false conclusion. Just because a foil may not look much like a wing
does not mean it doesn't act as a foil.
An oar is a big compromise, reached empirically without much science
(we're talking about rowing in general, I fear!). It functions in about
as complex an environment as you could imagine, running the gamut from
foiling to stall & back to foiling, with flow not only reversing along
its length but with a free surface (with air above) & a range of
vertical movements added as spice.
It'd be instructive to study the individual phases of the stroke, & from
that to derive more optimised blade forms for each individual phase. It
would then be fun to see which of this range of forms worked best
overall, & whether any worked better over the whole stroke than what we
have now - subject to the experiment also encompassing necessary
adaptations of technique to get the best out of each blade.
Cheers -
zeke_hoskin
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
I recant.
When I jumped to the conclusion that oars don't work much like
propellers, I should have concluded that oars don't work *exactly*
like propellers. I did not intend to assert that they weren't foils
and apologize for wording that might lead to that interpretation.
Actually, if you include Voith-Schneider propellers . . . I'm pretty
sure that FISA would object to blades that changed angle w.r.t the
shaft during the stroke, but at least it's another instance of blades
that transition from lift to stall and back in the course of a cycle
of operation.//Zeke Hoskin
Carl Douglas
>> its length but with a free surface (with air above)& a range of
>> vertical movements added as spice.
>>
>> that to derive more optimised blade forms for each individual phase. It
>> would then be fun to see which of this range of forms worked best
>> have now - subject to the experiment also encompassing necessary
>> adaptations of technique to get the best out of each blade.
>>
>> Cheers -
>> Carl
>>
>
>
> When I jumped to the conclusion that oars don't work much like
> propellers, I should have concluded that oars don't work *exactly*
> like propellers. I did not intend to assert that they weren't foils
> and apologize for wording that might lead to that interpretation.
Ain't nothing to apologise for - it gets us all thinking harder & it
gave you the opportunity to bring Voith-Schneider back to RSR :)
>
> Actually, if you include Voith-Schneider propellers . . . I'm pretty
> sure that FISA would object to blades that changed angle w.r.t the
> shaft during the stroke, but at least it's another instance of blades
> that transition from lift to stall and back in the course of a cycle
> of operation.//Zeke Hoskin
Eons ago on RSR, I can't recall how far back, we had a discussion of -
guess what? - hydrodynamic lift. I introduced the not unrelated action
of certain paddle-propelled vessels, where a system of linkages to
pivoted, shaped paddle blade continuously adjusts the blade alignment as
it passed below the surface to increase the "lift" element of the
process. In one of those postings ISTR mentioning cycloidal propulsions
systems, of which Voith-Scheider is modern representative.
Of course, there may be denizens of other newsgroups who will insist
that cycloidal propellers either can't work or don't involve lift & must
work by pushing water with their flattish blade faces....
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
Tinus
> URLs: www.carldouglas.co.uk(boats) &www.aerowing.co.uk(riggers)
http://upload.wikimedia.org/wikipedia/commons/5/56/VSPcycloide.jpg
the path of such a propeller already looks much like the path of a
rowing blade. Only difference being the lower, or nearly zero, drag
force.
Now, do we still need higher drag force around the perpendicular? (I
leave open whether this is done either by burying the blade deeper or
not)
mruscoe
> http://upload.wikimedia.org/wikipedia/commons/5/56/VSPcycloide.jpg
>
> the path of such a propeller already looks much like the path of a
> rowing blade. Only difference being the lower, or nearly zero, drag
> force.
>
Good interactive animation here: http://www.voithturbo.com/545950.htm
Click on "Hydrodynamic forces".
Kit
The Rocat http://www.rocat.co.uk/boat/rigger.htm has a "swing-arm"
gate that results in the blade movement WRT the boat being parabolic,
not circular, thus decreasing the time spent at the perpendicular and
increasing the edge-first blade movement through the water. Further
developments in this area could be interesting.
Carl Douglas
> On 9 Sep, 22:26, Tinus<martijn.weteri...@wur.nl> wrote:
>> On Sep 9, 8:43 pm, Carl Douglas<c...@carldouglas.co.uk> wrote:
>>> On 09/09/2010 17:55, zeke_hoskin wrote:
>>> Ain't nothing to apologise for - it gets us all thinking harder& it
>>> gave you the opportunity to bring Voith-Schneider back to RSR :)
>>
>>>> Actually, if you include Voith-Schneider propellers . . . I'm pretty
>>>> sure that FISA would object to blades that changed angle w.r.t the
>>>> shaft during the stroke, but at least it's another instance of blades
>>>> that transition from lift to stall and back in the course of a cycle
>>>> of operation.//Zeke Hoskin
>>
>>> Eons ago on RSR, I can't recall how far back, we had a discussion of -
>>> guess what? - hydrodynamic lift. I introduced the not unrelated action
>>> of certain paddle-propelled vessels, where a system of linkages to
>>> pivoted, shaped paddle blade continuously adjusts the blade alignment as
>>> it passed below the surface to increase the "lift" element of the
>>> process. In one of those postings ISTR mentioning cycloidal propulsions
>>> systems, of which Voith-Scheider is modern representative.
>>
>>> Of course, there may be denizens of other newsgroups who will insist
>>> work by pushing water with their flattish blade faces....
>>
>>> Cheers -
>>> Carl
>> http://upload.wikimedia.org/wikipedia/commons/5/56/VSPcycloide.jpg
>>
>> the path of such a propeller already looks much like the path of a
>> rowing blade. Only difference being the lower, or nearly zero, drag
>> force.
Which won't be a welcome observation among those of caustic tendencies,
but I sense they won't following this discussion.
Note also this one, showing the lift forces generated throughout the V-S
propeller's cycle:
http://en.wikipedia.org/wiki/File:VSPforces.jpg
>> Now, do we still need higher drag force around the perpendicular? (I
>> leave open whether this is done either by burying the blade deeper or
>> not)
Cycloidal propellers, being already fully immersed & mounted under the
bottom of a ship, escape the free-surface problem of the inadequately
buried oarblade. ;) Another reason why they are such effective
propulsion devices
>
> The Rocat http://www.rocat.co.uk/boat/rigger.htm has a "swing-arm"
> gate that results in the blade movement WRT the boat being parabolic,
> not circular, thus decreasing the time spent at the perpendicular and
> increasing the edge-first blade movement through the water. Further
> developments in this area could be interesting.
I wonder, in view of the parallel discussion on dynamic ergs, how many
of us are recognisable by this excerpt from that Rocat page:
"This is all due to the heavy rower (relative to the weight of the
boat), moving manically back and forth on a sliding seat"
?
Again the popular myth regurgitated, claiming it's the rower whot moves
manically (or maniacally?) back & forth when we all know (don't we?)
that it's the boat doing that oscillation under the sliding seat.
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
Tinus
> Note also this one, showing the lift forces generated throughout the V-S
> propeller's cycle:
> http://en.wikipedia.org/wiki/File:VSPforces.jpg
They've been a little bit opportunistic in drawing the sine function.
Of course there can be no drag force component into the direction of
the boat movement at the point where the blade is moving tangent to
the direction of the boat movement. This point necessarily exists. In
this picture they still draw a lift force at the perpendicular.
> >> Now, do we still need higher drag force around the perpendicular? (I
> >> leave open whether this is done either by burying the blade deeper or
> >> not)
>
> Cycloidal propellers, being already fully immersed & mounted under the
> bottom of a ship, escape the free-surface problem of the inadequately
> buried oarblade. ;) Another reason why they are such effective
> propulsion devices
Of course if one would be able to row a cycloidal rowing blade it
would be better. My claim was in relation to the currently existing
rowing blades and the believe that drag force at the perpendicular
must be increased by burying the blade deeper. To some extent
increased drag force is better in reducing losses to high water
velocities. However the higher drag force also increases the amount of
time spent in the stall phase so there must be some optimal point.
Tinus
> > Now, do we still need higher drag force around the perpendicular? (I
> > leave open whether this is done either by burying the blade deeper or
> > not)
>
> gate that results in the blade movement WRT the boat being parabolic,
> not circular, thus decreasing the time spent at the perpendicular and
> increasing the edge-first blade movement through the water. Further
> developments in this area could be interesting.
Isn't it exactly the opposite? The oar rotation depends on the oarlock
speed relative to the water and the speed of the blade relative to the
water. The faster the rigger slides the slower the oarlock moves
relative to the water. Isn't the rigger speed relative to boat highest
around the perpendicular?
Carl Douglas
> On Sep 10, 12:43 pm, Carl Douglas<c...@carldouglas.co.uk> wrote:
>> Note also this one, showing the lift forces generated throughout the V-S
>> propeller's cycle:
>> http://en.wikipedia.org/wiki/File:VSPforces.jpg
>
The one at the top? And maybe the one at the bottom? Perhaps they had
a few spare arrows & didn't want to waste them?
Tinus
> However the higher drag force also increases the amount of
> time spent in the stall phase so there must be some optimal point.
It increases the amount of energy spent, the time is actually reduced.
The consideration here is reducing drag force but move at the same
blade speed. The negative being less generated power (which needs to
be compensated by e.g. higher stroke rate), the positive being higher
efficiency.
Carl Douglas
> On Sep 10, 12:43 pm, Carl Douglas<c...@carldouglas.co.uk> wrote:
>> Note also this one, showing the lift forces generated throughout the V-S
>> propeller's cycle:
>> http://en.wikipedia.org/wiki/File:VSPforces.jpg
>
> They've been a little bit opportunistic in drawing the sine function.
> Of course there can be no drag force component into the direction of
> the boat movement at the point where the blade is moving tangent to
> the direction of the boat movement. This point necessarily exists. In
> this picture they still draw a lift force at the perpendicular.
>
>>>> Now, do we still need higher drag force around the perpendicular? (I
>>>> leave open whether this is done either by burying the blade deeper or
>>>> not)
>>
>> bottom of a ship, escape the free-surface problem of the inadequately
>> buried oarblade. ;) Another reason why they are such effective
>> propulsion devices
>
> Of course if one would be able to row a cycloidal rowing blade it
> would be better. My claim was in relation to the currently existing
> rowing blades and the believe that drag force at the perpendicular
> must be increased by burying the blade deeper. To some extent
> increased drag force is better in reducing losses to high water
> velocities. However the higher drag force also increases the amount of
> time spent in the stall phase so there must be some optimal point.
We're in the land of the trade-off, whereas most rowers are left cold or
confused by these discussions :(
Assuming a rower is going to make the greatest investment of effort into
the stall phase, where the return is lowest, I'd always go for a higher
drag coefficient during that stall & this is achieved only by going deeper.
If the stall comes with with a very low Cd (i.e. a shallow stroke), then
the stalled part of the stroke will be longer & have more rapid slip, so
there'll be 2 reasons for a higher energy loss, & there'll be more
aeration both before & after the stall, with consequent impairment of
lift performance. It sounds like lose, lose, lose & lose to me, with no
up side (unless the guys doing this are in the other boat).
Tinus
> If the stall comes with with a very low Cd (i.e. a shallow stroke), then
> the stalled part of the stroke will be longer & have more rapid slip, so
> there'll be 2 reasons for a higher energy loss, & there'll be more
> aeration both before & after the stall, with consequent impairment of
> lift performance. It sounds like lose, lose, lose & lose to me, with no
> up side (unless the guys doing this are in the other boat).
I was thinking about a low Cd but the same blade speed. In this case
there is a win. But I totally agree there is a loss because the rower
has is disabled in applying as much power as possible. But, rowers
have limited power so when they are at their limit of power they can
start to think about re-distributing their power.
IPS
Why don't we simply move the rower as far through the work as
possible, tweak the rigging and oars, and essentially finish the
stroke when the blade is in the stall phase; giving up on the lift we
conventionally get at the finish? Isn't this what the US woman
sculler Michelle Guerette basically achieved at the Olympics?
Carl Douglas
> On Sep 10, 6:19 am, Tinus<martijn.weteri...@wur.nl> wrote:
>> On Sep 10, 2:59 pm, Carl Douglas<c...@carldouglas.co.uk> wrote:
>>
>>> If the stall comes with with a very low Cd (i.e. a shallow stroke), then
>>> there'll be 2 reasons for a higher energy loss,& there'll be more
>>> aeration both before& after the stall, with consequent impairment of
>>> lift performance. It sounds like lose, lose, lose& lose to me, with no
>>> up side (unless the guys doing this are in the other boat).
>>
>> I was thinking about a low Cd but the same blade speed. In this case
>> there is a win. But I totally agree there is a loss because the rower
>> has is disabled in applying as much power as possible. But, rowers
>> have limited power so when they are at their limit of power they can
>> start to think about re-distributing their power.
>
> Why don't we simply move the rower as far through the work as
> possible, tweak the rigging and oars, and essentially finish the
> stroke when the blade is in the stall phase; giving up on the lift we
> conventionally get at the finish? Isn't this what the US woman
> sculler Michelle Guerette basically achieved at the Olympics?
The idea of the all (or mostly) lift-phase sculling stroke may first be
due to Volker Nolte - original thinker & great experimenter in rowing.
IIRC, this was implemented, in part, by hanging the oarlock ahead of the
pin so that the button itself swung forwards & outwards during the stroke.
And I think you see something akin to this (whether by design or
accident) in the Rocat rig geometry.
Nolte's idea, IIRC, was to end the stroke just as the stall began to
develop - i.e. square with the boat.
I suspect one problem in implementing this might be that to finish well
at the very point where the hands must be moving their fastest presents
problems for speed & dexterity.
It would be interesting to hear our alkaline friend's more considered
views on all of this. Sadly, since Phil's interesting posting he seems
to have been struck dumb, both here & in the thread on RI to which you
had first drawn our attention.
IPS
Layback http://www.rowingillustrated.com/boards/viewtopic.php?f=16&t=1688&p=50042#p50042
Carl Douglas
> He's instead enlightening us in the thread about Long Layback vs. Less
> Layback http://www.rowingillustrated.com/boards/viewtopic.php?f=16&t=1688&p=50042#p50042
>
Ah!
So Spracklen's crews with long laybacks were slow, inept & incapable of
winning races?
I'm just tickled by the notions that:
1. You can separate your weight from the boat at the finish. How?
Skyhooks anyone?
2. That recovery from a long finish must dip the bows. Why?
Oh dear!
pdb
> On 11/09/2010 13:37, IPS wrote:
>
> > He's instead enlightening us in the thread about Long Layback vs. Less
>
> Ah!
>
> So Spracklen's crews with long laybacks were slow, inept & incapable of
> winning races?
>
> I'm just tickled by the notions that:
> 1. You can separate your weight from the boat at the finish. How?
> Skyhooks anyone?
> 2. That recovery from a long finish must dip the bows. Why?
>
> Oh dear!
> 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)
I also thought that the movement of the hands around the finish needed
to be smooth and continuous, bringing the body forward. How can this
bury the bow? Now my greatest concern when sculling is burying the
stern by not deccelerating as I approach frontstops; I remember
watching Doug Melvin at Chester Regatta in 1972 whose boat remained
level - an inspiration!
The pleasure of making the boat proceed smoothly through the water
cannot be beaten - the real challenge is to do this at maximum effort.
Maintaining the speed of the hands 'around the turn' is an essential
component of the perfect stroke and stops the bow being buried.
Charles Carroll
> must be increased by burying the blade deeper.
Carl,
Does the data support this?
Consider Kleshnev's studies and conclusions.
"It is also important, that the first crew increases the force by
means of faster leg drive, good connection with the trunk work and
more horizontal and shallower blade path . . . " (RBN February 2004)
I found this yesterday after having delivered a lecture that to my
embarrassment was all wrong.
The "more horizontal and shallower blade path" was disturbing.
But it also corroborates what I observe as I scull.
Want to go faster?
Simple!
Train yourself to be quick increasing force at the beginning of the
drive, D1-D3, get the heels down against the footplate as fast as you
can, kick against the footplates, grab with the arms, keep the
connection, keep the blade path horizontal, and keep the blades it as
shallow as you can.
Cordially,
Charles
Carl Douglas
I hold Valery Kleshnev & his work in the highest regard, which does not
mean that I necessarily agree with all he says.
Similarly, we are all learning, so what we believed 6 years ago may or
may not have undergone change over that period.
Without question, a shallow blade in the midstroke entrains air behind
it, undergoing a consequent total loss of the water-to-back-of-blade
adhesion which is the improbable but real tensile linkage that provides
the far greater part of your connection with the bulk of the water
during the stroke. That's the downside of a shallow blade, & it's one
which most crew rowers have, perhaps unintentionally exploited to their
temporary advantage (AKA washing out) when the going gets too tough &
they can't keep up with the rest.
So at what point do you go from an over-shallow blade to one that is too
deep? Ask that question of a whole lot of very fast scullers, who seem
many of them to bury pretty darned deep. I guess they must be getting
it all wrong?
Let me chuck in what I think on your side of the pond is called a curve
ball, & on our side might be termed a googly:
Consider the stroke that moves a heavy traditional lugging boat - e.g. a
"whaler" in UK parlance. These are rowed with straight blades & with
strokes which are short & dig deep. If your row a shallow, sweeping
stroke, it just doesn't work as well.
Cheers -
Carl
PS Turned that old sideboard into a bassoon yet ;)
C
Richard du P
> .......... That's the downside of a shallow blade, & it's one
> which most crew rowers have, perhaps unintentionally exploited to their
> temporary advantage (AKA washing out) when the going gets too tough &
> they can't keep up with the rest.
>
Yes Carl, definitely! I can attest to stroking a couple of humble,
happy and reasonably successful college crews in the 1960s, and
wondering for many years afterwards, how I kept up with the bigger,
stronger and fitter comrades behind me, while rowing a longer stroke.
Photographic evidence bears out what you say ..... and there I was,
delighting the coaches by being the only one who was doing exactly
what they asked .....
> Consider the stroke that moves a heavy traditional lugging boat - e.g. a
> "whaler" in UK parlance. These are rowed with straight blades & with
> strokes which are short & dig deep. If your row a shallow, sweeping
> stroke, it just doesn't work as well.
>
That one takes me back even further - the blazing summer of 1959, I
think - when I was having a fairly miserable time at what was then a
rather boneheaded Rowing School - one of only two I believe, which
both played cricket at Lords and rowed at HRR [and not the one you've
heard of]. Like many schoolchildren of that era I was in the Combined
Cadet Force [I was the fattest little member of the 5th Glosters,
polishing my back cap badge every week] training with the
superabundance of basically Great War equipment which the UK had left
over from WW2.
We went on a "Camp" at an Royal Engineer base near Weymouth, doing
stuff in the piece of water behind Chesil Beach, which culminated in
competitive exercises against another [non-rowing, part of Jeffrey
Archer's life] school ..... we just totally knew that we'd murder them
at rowing big untidy craft with blunt ends ..... and alas they just
totally murdered us. I guess the poor lambs had never been told
to ..... see where the blade floats in the water ..... and draw it
through at exactly that height .....
I wonder whether I've enough time left, to understand ALL the things
I've cocked up in one short life?
Richard du P
Carl Douglas
> On Sep 11, 1:49 pm, Carl Douglas<c...@carldouglas.co.uk> wrote:
>> On 11/09/2010 13:37, IPS wrote:
>>
>>> He's instead enlightening us in the thread about Long Layback vs. Less
>>> Laybackhttp://www.rowingillustrated.com/boards/viewtopic.php?f=16&t=1688&p=5...
>>
>> Ah!
>>
>> winning races?
>>
>> I'm just tickled by the notions that:
>> 1. You can separate your weight from the boat at the finish. How?
>> Skyhooks anyone?
>> 2. That recovery from a long finish must dip the bows. Why?
>>
>> Oh dear!
>> Carl
>
> to be smooth and continuous, bringing the body forward. How can this
> bury the bow? Now my greatest concern when sculling is burying the
> stern by not deccelerating as I approach frontstops; I remember
> watching Doug Melvin at Chester Regatta in 1972 whose boat remained
> level - an inspiration!
>
> The pleasure of making the boat proceed smoothly through the water
> cannot be beaten - the real challenge is to do this at maximum effort.
> Maintaining the speed of the hands 'around the turn' is an essential
> component of the perfect stroke and stops the bow being buried.
I couldn't agree more on the objective of smooth progress, yet I don't
see how speed of hands at the finish contributes to this, or to
preventing the bows from burying.
The rate of change in rate of rotation of the large mass of your body
(in particular shoulders, arms & head) about a transverse pivot near the
seat is what generates the couple which, in turn, depresses the bow (if
bow depression occurs). If you perform a stiff-backed & rapid
sternwards rotation of the upper body, that will bounce the boat & push
down the bows. Yet such actions are encouraged by a popular belief that
it is important to "get your weight out of the bows".
No, it isn't necessary to remove weight from the bows. And note that it
is the rate of change, i.e. the acceleration, which generates the
undesirable couple. If you had no time to get forward, all kinds of
extreme measures might be appropriate. However, we agree that
smoothness is our objective. And we have lots of time to get forward.
So, as one objective of the recovery is to sustain an even hull speed
through the water, & as sudden sternwards motion will not just bounce
the bows but also make the boat surge when already running at peak
speed, it makes better sense to move less violently. It is also less
strenuous & less disturbing of the boat to not so much rotate a ramrod
back (I know that was not being suggested here, but I mention it as
another common concern) as to curl the body sternwards, thus minimising
the length of arc through which large masses are moved at the start of
the recovery.
At the finish of a good stroke there is little or no tap-down. For the
blade to emerge neither scraping water nor backwatering the hands must
descend as they move into the bow since a vertical tap-down will
certainly involve the water overtaking any still immersed part of the
blade. So there is a relatively complete cessation of bow-wards hand
movement WRT the boat (but _not_ WRT the water!) which, with no further
downwards movement, indicates that the hands must first stop & only then
start moving astern. As I see it, that must make a constant hand speed
around the finish an impossible concept.
Cheers -
Carl
--
Carl Douglas Racing Shells -
Fine Small-Boats/AeRoWing Low-drag Riggers/Advanced Accessories
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