Re: [Paddlewise] A new way to teach the forward stroke?

I wrote:
> In fact, some of that misdirected
> energy is taking the load off your "paddle holding up" muscles.

Niels responded:
>>>At the front of the stroke: Yes. At the back of the stroke: Exactly
opposite.
In the seakayer I put online (
http://www.nibla.nl/tmp/paddlewise/ExampleStroke/ ) I see the blade
going in at 45 degrees and comes out at 45 degrees. The forces up and
down through the whole stroke cancel out.<<<<<

Below you seem to contradict this (and correctly I think). Given your pivot at
the shoulder model and gravitational paddling theory, any resistance to the
blade (and even the falling of the blade before it meets water resistance)
throughout the stroke should allow the paddler to relax the paddle holding up
muscles except when lifting the hands and paddle out of the water to prepare
for the next stroke.

>>>>Assuming his hands and paddle on a scale would measure 7 kilos (70N),
and he lifts the center of his paddle (which is the center of gravity)
40 centimeters each second, I calculate that each second he expends
0.4*70 (force * distance) = 28Nm of energy. Since he does that every
second (which he does), that 28W.<<<<<<

You must have very heavy arms or a really heavy paddle. Maybe you agree with
Derek H. who (at least years ago) advocated using a heavy paddle because he
felt it added "momentum" to his stroke. Personally, I like to use the lightest
paddle with the lightest blades I can (given enough strength to have a durable
paddle). My paddles weigh about .6 of a kilo total and my arms (out at my
hands if relaxed at the shoulder but held straight at the elbow) weighed in at
less than 1.5 kilos each (when resting on a scale at shoulder height so the
arm is level). So all the potential energy I'm going to get is only going to
be the result of half of what you are claiming for arm and paddle weight.
Furthermore, I think you may be also exaggerating the force by measuring the
middle of the paddle going up and down and using the weight of both arms for
each stroke. Since once the blade is in the water and meeting resistance only
one arm is lifting about 1/2 a paddle to get into position for the next
stroke. Have you thought about measuring how much each hand goes up and down
and using the weight of just that arm and 1/2 the paddle weight to calculate
the potential energy available for gravitational propulsion? I think the
efficiency of paddle propulsion is less than 50% so the higher you lift the
paddle the more energy you waste in the transfer to boat propulsion. Since it
is easy to do 3 knots with a low, elbows at the side, Eskimo type stroke
(driven by a small waist pivot) why keep working against gravity and wasting
more than half the energy you put in to lifting the paddle just so you can
teach a sprint racing stroke because that's what everyone else around you
teaches. Why not risk the ire of the governing bodies, who's main mission is
trying to train future racers, by pointing out how wasteful that racing stroke
is for those paddlers just wanting to put around at a nearly effortless 3
knots. BTW, you don't need an Eskimo replica paddle to use the Eskimo stroke.
I do it all the time with a feathered Euro paddle. Perhaps that is one reason
why it doesn't bother me to go very slow, I'm not having to hold up the paddle
weight (as little as it is) using my trapezoids and can just rest it on my
cockpit between strokes if I want because I don't have to lift it hardly at
all to use it again from that position.

>>>>>OF COURSE there will be energy loss in turbulence - as in any other
stroke. The part I'm talking about is the energy conversion of potential
energy into force and movement, BEFORE it is dissipated by the water.
All I'm saying is that the 30W of output ends up pushing water, in
whatever direction it might be.<<<<<<<

Do you agree that the power available to drive the kayak is whats left after
much of that potential energy has been disapated? Maybe you should measure the
power using how far the paddle falls before it encounters resistance from the
water (or how much you had to lift it when it was out of the water and not
being supported by the drag due to the paddle blade in the water holding it
up). Since my potential energy available doing the same thing will be far less
than 30 watts (due to light paddle and arms) and probably far less than that
half that will be directed to moving the kayak I don't see of what importance
is a high potential energy if most of it will be later wasted and you had to
put an equal amount of kinetic energy into the system lifting the arms and
paddle to have the potential energy be that high in the first place.


>>>>>>>You'd agree that, in a vacuum, there would be no losses? That's all I
wanted to say. Then again: In a vacuum my kayak wouldn't slow down when
I stopped paddling, so in a vacuum the question is not valid.<<<<<<

No, if the spring is metal (and therefore not a perfect spring) there will be
heat losses from the movement of the spring's molecules against each other. I
will agree that since we live in the real world of friction and energy losses,
accelerating against a drag is a large user of energy, much more than from
just maintaining a constant speed. Which was my original point before, you
began using what I consider an unrealistic example by operating in a vacuum.

 I wrote:
> Those muscles get a rest because some of your paddling energy (where ever
it
> comes from) is resisting the paddle sinking because of the blade angle at
> entry.

Niels responded:
>>>>>Think of my model. I can keep its arms from falling down by pushing
horizontally against the paddleblade. (I'll film it if I have to).
There's no need for any upward force from the outside: Your shoulders
will take care of it, without the use of any muscles.<<<<<

I was wrong and you are correct here, the fall and then the resistance all
through the stroke (pivoting freely from the shoulders) is allowing the paddle
holding up muscles to relax. This does seem to contradict your earlier
statement though, that things are just the opposite when the water is being
lifted at the end of the stroke. Even then it is retarding the paddle and the
paddle holding up muscles can be relaxed (but before then the energy from
gravity will have likely been so completely dissipated that what little
residual energy is left is now having to lift water against gravity and will
have stopped the (relaxed gravity powered) stroke from getting that far
anyway.


>>>>> That's assuming that the water will carry a substantial part of the
weight of at least your downward blade. What's the volume of a blade? I
hardly think the buoyancy could be significant, compared to the 3 to 4
kilo weight of one hand and half a paddle.<<<<<<

That depends on the volume of the blade and the weight of your arms and
paddle.

Niels wrote:
>>>>>>> You have to use some muscles in the shoulder of your upper arm, to
keep
> the paddle from falling over your lap. That force can be directed
> strictly sideways. Apart from that, no muscles are needed. While the
> arms fall down, the blade moves practically horizontally through the
> water, directing the force exactly where we want it. Using muscles to
> keep the paddle up in any other way would be counter-productive.<<<<<
>
I asked:
 I don't understand what you are trying to say above. Can you give me a
better
> description and explain why? And where is it we want the force directed and
> why there?

Niels responded:
>>>>>>You seem to think that I'd HAVE to put an upward force on the paddle to
keep it in check. I don't: The horizontal force of the water will do fine.
Do I need to make a new video, showing how I can keep my model in check?<<<<<

I'm more confused than ever. Please provide a detailed description of what you
mean here. As best I can see you are using your upper arm to lift half the
paddle up against gravity to get the potential energy for the next stroke, but
your mechanical model has both arms falling down to power the stroke (and both
must be lifted on the model to set up the next stroke--sort of like a high
kneel canoe stroke). How do you do this with a sideways directed force? How do
your get up...from sideways? I'm really confused and need a much better
description of what you mean here.

I wrote:
> A buoyant blade would bob up and down during the stroke sinking from the
> gravitational energy (then holding up the paddle) and propelling it back up
> again to get some more of that potential energy that you seem to like to
use
> back (and for free).

Niels responded
>>>>>>I think such a bobbing paddle would _hamper_ the use of potential
energy. The blade _should_ be allowed to go down freely: Only the
horizontal force can be put to good use, so all other forces are best
kept minimal.<<<<<<

Why do you think that? It seems to me that if the buoyancy bounce were timed
right, you could save your muscles from needing to accelerate the paddle as
much in lifting it against gravity. Some paddlers (including some of those who
like traditional native type wood paddle) like a buoyant blade and feel that
this helps them use less energy because of this rebound. Since the kinetic
energy is being rapidly disapated anyway as soon as the blade contacts the
water most will probably be gone before the blade ever gets to vertical
whether it is buoyant or not. A buoyant blade will save you from much of the
distance you will have to lift this paddle thereby cutting your loses inherent
in the transfer of energy (from lifting the arms and paddle against gravity
into the forward motion of the kayak).

I wrote:
> During paddling the blade hardly moves at all once it is planted in the
water.
> It has so much drag that the kayak is pulled past it while it moves very
> little in the opposite direction.

Niels responded:
Back to my example-paddler at
http://www.nibla.nl/tmp/paddlewise/ExampleStroke/ :
In the video, there's little reference on the water or in the background
to see how far the paddle moves. Judging just from the splashes, I'd say
that his hands remain almost stationary above the water, but the blade
underneath moves quite a bit (Close to a METER at the tip).

You are wrong here. The stationary pivot point of a paddle during a stroke is
near the water's surface (and with especially long blades may even be below
the surface--wasting some energy pushing the upper part of the blade the wrong
way--forward in the water, partly retarding the other part of the paddles
propulsion). Try paddling near some lily pads or other fixed objects in the
water and watch where the paddle goes into the water and where it comes out of
the water. I'll bet you will see it is at the same place. You could also look
at a video of a paddler moving across the TV screen and using stop action and
a small sticker find the point on the paddle shaft that is stationary during a
stroke. Wing paddles can even come out of the water slightly ahead of where
they went in because of their 'lift" in the water. So the tip of the blade
will only sweep out a distance equal to the change of angles of your paddle
shaft during the stroke measured from that stationary pivot point to the blade
tip. Since the center of power is even nearer to the pivot point than the
blade tip you should see that your estimate of a meter of paddle motion is
much too large.



>>>>The position against-the-dock is introduced for two reasons:
- - To check if there IS a position of rest to be found;
- - To give students time to find that rest.
There surely will be differences with actual paddling, but no
differences that affect the purpose of the dock-exercise.<<<<<<

Since with every reasonable kayak stroke there is a rest for the paddle hold
up muscles I don't see why it needs looking for by a student. Okay, maybe if
they are using what you call the "rental stroke". Please describe the rental
stroke, as I'm not sure what you mean. The fiberglass rental kayaks I see
often have the gelcoat worn off where the paddle slides across the deck near
the front half of the cockpit. It seems some new paddlers a least have solved
the paddle lifting muscles problem much like you did by supporting the paddle
in the middle. The first time I went paqddling I had sore trapezoids the next
day. I must not have used them much before because even if I didn't paddle for
many months I have never had sore trapezoids from paddling since then. Or
maybe I learned how to not need them to hold up the paddle after that first
time paddling.

I wrote:
> BTW, I have no trouble going slower if that is what my paddling partners
are
> doing. I'm curious to hear an explanation as to why from those who seem to
> have trouble doing that. Are you all using wing paddles (that just don't
work
> right at slow speeds) or is there some other reasons? Psychological maybe?

Niels responded:
>>>>If (and only IF) my hypothesis of using potential energy is valid, then
_that's_ the reason. To paddle slowly, you'd have to keep that energy in
check - by straining muscles that otherwise could be at rest.<<<<<<

I don't see why you don't just take a rest between your strokes (at the end of
a stroke) then. If the other paddles are going considerably slower than your 3
knot pace it hardly matters if your stroke is then less efficient because, as
you yourself pointed out, just going slower is a more efficient way to paddle
a given distance anyway.
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