[Paddlewise] paddles

Peter wrote:

>Get the idea of "slippage" out of your vocabulary when considering fluid 
>generated thrust.  Power is a work rate, to define efficiency with anything 
>other than "power in", or reduce it to something not related to power, is 
>clearly invalid.

Peter may want to get it out of his mind but the following references consider
it an important point.

Durand, Resistance and Power of Ships pp 163,211

Taylor, Speed and Power of Ships p 85 (Taylor has some nice graphs showing the
loss in efficiency with increasing slippage)

Rawson & Tupper, Basic Ship Theory p 353

Society of Naval Architects and Marine Engineers, Principles of Naval
Architecture pp 137,151, 173,

Gilmer, Introduction to Naval Architecture pp 232-233, 236, 237

OK, still not convinced? Try these little tests in your own kayak. Turn the
paddle so it travels through the water edgewise and paddle to a buoy a mile
away. Call me when you get there. Now turn it so it travels normal to your
intended direction and paddle back. You can do the same experiment with your
traditional style paddle. Just angle the blade so it slides neatly through the
water with the least resistance. In both cases you have experienced the loss
of efficiency through increased slippage.

I will resist the temptation to refute all of Peter's long diatribe since most
of you have probably gotten bored by now. Nevertheless this may help you
understand paddle efficiency. 

Paddles actually act very much like sails. Downwind the sail creates driving
force in a primarily drag mode just as your paddles does when drawn straight
back through the water. Upwind the sails generate driving force primarily
through lift. (Has the little light begun to flicker on in the heads of
sailors? :-)) The fastest and most efficient point of sail is reaching. Now,
what configuration of sail works most efficiently when reaching? (The light
should glow brightly) Research and practical experience have shown us that a
sail plan with an aspect ratio of 1:1 provides the greatest amount of
propulsive force on a reach. (See Marchaj, Sailing Theory and Practice p. 179). 

Of course, we must use care applying this. Sails operate in a steady state
(the wind blows more or less steadily) but paddles use a herky jerky start and
stop motion (the reason for my interest in starting vortex losses).
Nevertheless, tank tests confirm that paddles do seem to perform in the same
way although I think most would like more tests covering more variables.

Despite many claims I have not seen any test data that suggests that high
aspect ratio paddles have higher efficiency. Perhaps one of the proponents of
the high aspect ratio paddles has done objective testing that they can share
with us. 

Now, on to the system. 

Clearly we would like to match the paddle to the paddler (Over ten years ago I
proposed this very concept in some articles in Canoesport Journal ) and, in
that way,  produce as much speed as possible for a given power input. Most of
us sedentary types react unfavourably to stress and strain on our old joints
and muscles so we prefer paddles that do not feel like we have immersed them
in concrete. An interesting side note. Renn Crichlow the one time K-1 gold
medalist once told me that the wing paddle felt exactly like he had stuck it
in concrete when he used it properly. Presumably he had done some paddling in
a construction site.

So, paddles that have more slippage (less efficient paddle) "feel" good and we
make up for the loss in blade efficiency by using more velocity. The net gain
comes in the form of overall efficiency in the system and that, I believe,
prompted Michael to write:. 

>But we're really still arguing two separate issues. My position was that
>a human is more efficient at producing lower output over a long period
>of time than at producing high output for a short time. Biomechanical
>studies bear that out, and that is why narrow paddles tend to be better
>for distance paddling

This raises some questions. Why does a narrow (I think he means high aspect
ratio. Correct me if I assume incorrectly, Michael) paddle work better? What
characteristics does a high aspect ratio paddle possess that makes it feel
better than a low aspect ratio paddle? Can we not duplicate  those
characteristics with a low aspect ratio blade? If not, why not?  Matt Brose
asked a similar question and I don't think he got an answer.

I think the proponents of the high aspect ratio paddles have assumed some
properties for those paddles that simply cannot be duplicated with any other
type. My own tank test experiments and research by others suggests otherwise.
Perhaps they need more experience with a wider range of low aspect ratio
paddles. In any case, the type of paddle you use really does not matter so
long as you still enjoy your paddling. What does matter is evangelism based on
poor and unsupported theory. 


Cheers,

John Winters


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