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

Niels Blaauw niels_at_nibla.nl wrote to Peter:

>>>>>>While the arms move downward, the paddle-blade does not. Assuming you
keep you elbows locked and move your arms down from the shoulders, both
your hands and your paddleblades will travel in a circle around your
shoulders. I made a drawing:
http://www.nibla.nl/tmp/paddlewise/halfway.gif
You see that, while the hands are moving down, the submersed blade is
mostly moving backwards.<<<<<<<

Only at one point is it moving directly backwards. At all other points of the
rotation it is less efficient as energy is being directed at some angle to the
direction you are trying to drive the kayak. In fact, some of that misdirected
energy is taking the load off your "paddle holding up" muscles.

>>>>>When watching the animation from my link, I see the center of my paddle
rise and fall for about 30/40 centimeters, once more indicating about
20/30 watts of power from potential energy. I maintain that most of the
energy is going into backward force and movement, having nowhere else to
go.<<<<<<

Could you run through just how you calcutated the 20 to 30 watts of power due
to lifting the paddle and arms? Nowhere else to go? How about it going into
other directions than directly driving the kayak and also going into
turbulence in the water (heat) the stroke and blade are causing.


Niels Blaauw niels_at_nibla.nl wrote to me:

>>>>>>My own kayak-club maintains a speed of around 3
knots, in various touring and sea-kayaks. Do you agree that about 15
watts should do the job for that kind of speed?<<<<<

I use horsepower, one of which I see equals 745.7 watts. My Vista computer
won't open the chart I made in an Excel spreadsheet back in 1994 due to what
it says are my registry settings (if anybody can tell me how to change the
settings to be able to open my old files I'd sure appreciate it). Anyway I
cranked up my older computer and I see it takes about 9.3 watts to move a
Coaster kayak (13' 5" x 23" x 40 pounds) with a 150 pound paddler at 2.9
knots, and 18.5 watts to go 4.2 knots. It takes about 56 watts to get it to
4.86 knots and 85 watts to get it to 5 knots (which is very near hull speed
for the 13' 5" long Coaster--one of Sea Kayaker magazines strongest testers
averaged 5.2 knots in a Coaster for one nautical mile--paddling all out). It
would take 124 watts to drive the Coaster plus 150 pounds 5.5 knots and 150
watts to drive it at 5.8 knots.

>>>>>>>Matt, come on! The slower you go, the more efficient you are in energy
per distance. So, the more often you let your kayak slow down, the more
efficient you get.
Just accelerating and decelerating doesn't cost any energy, unless you
put on the brakes. Look at a weight on a spring: It keeps bumping up and
down forever.<<<<<<<

We don't live in a vacuum. Drag due to friction is always putting on the
brakes. You are more efficient travelling a given distance by going slower
because there is less drag at a slower speed. But if you are trying to
maintain a speed (even just 3 knots) with a paddle stroke you don't want to
slow down much between strokes because accelleration is needed to get back up
to above 3 knots again (to maintain the average of 3 knots). Even without the
necessary accelleration effort to regain the lost speed the time spent going
faster than 3 knots uses more energy resisting the greater drag than the time
going slower than 3 knots does when your speed varies. Drag due to wetted
surface friction (which is the vast majority of drag at three knots) increases
at the 1.83 power (nearly the square).

>>>>>>So you think the "vertical rest" is a valid principle, at least for
those specific muscles? Since those muscles tire the most quickly in my
students (and myself) it's worth pointing out a way to give them some
rest.<<<<<<

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. But he main reason that paddling is easier than just holding up the
paddle is because you are alternately tensing and relaxing the "paddle hold
up" muscles as you stroke from one side to the other which is a lot easier for
us to do than to hold our muscles in tension all the time in a static
position.

>>>>>>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 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?

>>>>>I don't think it would work. I paddle in shallow water sometimes, where
I put my blade in the bottom and push myself forward. It's very awkward,
and not just because of the increased drag of the kayak. It's just very
uncomfortable to keep your blade at a fixed depth in the water.<<<<<

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). It would not make the paddle act like pushing off the
bottom or paddling in very shallow water unless it was hugely buoyant.

I wrote:
> Paddling against a dock is not a good representation of what happens during
a
> stroke because when the boat doesn't move the paddle must be pulled through
> the water rather than remain planted rather solidly in the water while you
> pull the sleek (compared to a paddle) kayak through the water.

Niels responded:
>>>>If I put force on a paddleblade in the water, it will drag through it.
The blade doesn't know or care whether there's a kayak and whether it
moves: When there's force, a blade will drag through the water. Always.
As I say in my video: Against a dock, the stroke will take more time,
giving a better feeling of the "rest". Apart from that, there's no real
difference.<<<<<

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. When you hold the kayak from moving (with a
dock at the bow or rope fastened to something at the stern) the paddle blade
slowly slogs through the water and makes the paddle stroke unbearably long
(those muscles remaining tense too long again maybe). A paddle doesn't know or
care about anything at all. but that is because It has no brain. There are a
lot of differences between the two situations. One I forgot to mention when I
talked earlier of the advantages of the wing stroke (even for a non-wing
paddle), is that that sliding to the side stroke prevents the sensation of
paddle flutter (since it only flutters in one direction rather than winging
back and forth like a falling leaf during the stroke as a paddle pulled
straight back tends to do. Flutter is worse when accellerating and far worse
when the kayak is fixed in place while pulling the blade through the water.

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?
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