Re: [Paddlewise] wing theory

On Friday, June 6, 2003, at 11:13  AM, Gerald Foodman wrote:

> I have been thinking about the wing and wonder if the following makes 
> sense.
>
> First a note on efficiency, which by
> definition is the amount of energy loss, between the place you put 
> energy in
> and the place you take it out.  If you imagine a perfectly vertical 
> paddle,
> drawn straight back parallel to the boat, then, BETWEEN THE BLADE AND 
> THE
> BOAT'S FORWARD MOTION, there is no energy loss at all, INDEPENDENT OF 
> THE
> SHAPE OF THE BLADE.  (100% efficiency.)  This is because all the work 
> you do
> on the paddle goes into moving the boat forward.  The paddle could be
> square, or have holes in it and efficiency is still 100%.  The paddle 
> is
> just generating drag and changing the drag coefficient has no effect 
> energy
> loss between the blade and forward motion.

You are mistaking drag (a force) for energy. While it is true that for 
every Newton or pound of force generated by the paddler a equal and 
opposite unit of force is applied to the paddle by the water. All the 
force generated by the paddle is indeed transfer to the boat to make it 
move. This does not mean that all the energy is transferred without 
loss. The surest way to verify this is to look at the water. If there 
is any sign that the water moves at all due to the paddle, you must 
assume that there has been energy added water by the paddle. Moving 
water indicates kinetic energy in the water that could have been 
kinetic energy for the kayak. If there is energy in the water from the 
paddle that could have gone towards moving the boat, you must assume 
that the paddle is not 100% efficient. There is no such thing as a 100% 
efficient paddle. This is true regardless of the orientation of the 
blade or its direction of motion.
>
> Changing the size of the wing blade, or length of the paddle changes 
> the
> gear ratio, just as for the conventional paddle, and should be chosen 
> for
> the best efficiency of the particular paddler and the particular
> distance/speed he is racing.  The paddler is a motor, and like any 
> motor, is
> most efficient at a particular speed, which is generally not the speed 
> for
> maximum torque.
>

Changing the size of the blade does not change the gear ratio. The 
"gear ratio" is only related to the length of the paddle. Changing the 
size of the blade changes the speed at which it moves through the 
water, in other words it changes its efficiency. This is more analogous 
to having a bicycle chain skip or jump on the gears or having the gear 
rotate slightly relative to the peddle. Changing the blade size does 
effect the perceived gear ratio because for a given cadence it will 
take less force, and for a given force it will require a higher cadence.

There are good reasons why people don't use huge blades on their 
paddle, but everything else being equal, smaller blade area means lower 
efficiency. There are practical reasons like a paddle with 4' x 8' 
blades would be hard to fit in the car, would be heavy and would just 
be awkward to swing around. You need to be able to get a paddle in and 
out of the water fairly easily and the physical construction of humans 
place certain limits on what is practical and comfortable. And 
diminishing returns means that at some point the added efficiency just 
isn't worth the other problems which come with large size.  The right 
balance of overall efficiency of the paddle and comfort for a given 
paddler will effect the optimum size for the paddler.
Nick Schade

Guillemot Kayaks
824 Thompson St
Glastonbury, CT 06033
USA
Ph/Fx: (860) 659-8847
http://www.guillemot-kayaks.com/

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