[Paddlewise] lift and efficiency

Mind if I make an attempt at a more rigorous definition of some
potentially confusing terms?

... oh goody....

Lets talk about efficiency for a moment.

Loosely defined, efficiency means the ratio of power output over power
input. Ealier, John Winters quoted some efficiency numbers, .92 for modern
wind paddles, .86 for regular modern paddles. He didn't state the exact
application of the these numbers, but I would hazard a guess that it means
that for every 100 watts of paddler effort, 92 watts of are translated
directly into forward motion of the boat (86% for regular paddles). The
other 8 watts are lost due to turbulence, slippage of the paddle through
the water, flexing of the paddle shaft, etc... Note the difference between
the two kinds of paddles is not that great at six percent.  However for
racers, six percent is tremendous. For the average paddler, six percent is
probably less important, although I will not call it insignificant. The
efficiency contrast of the two paddles may be even smaller at recreational
speeds. I have no idea where a greenland paddle would fall into an
efficiency measurement, although I think another part of the benefit of
greenland paddles for touring is that it facilitates the use of many
different muscles all in the same day. I wonder if modern science can
quantify that benefit.

Ok, now lets talk about lift... but first lets talk about drag. The
paddler is pulling backwards on the paddle (force vector points towards
the stern). The resistance of the water (drag) on the paddle resists that
pull (force vector points towards the bow). The drag force vector is
slightly smaller than the paddler force vector, which is another way to
think about efficiency. The difference in the size of the vectors
represents the energy that is lost due to turbulence and the slippage of
the paddle through the water. When lift is generated due to laminar flow,
the size of the resistance vector is slightly increased because the lift
vector points in the same direction as the drag vector. Even if further
calculations were to show that the lift generated by Greenland paddles
really is insignificant, efficiency is probably still increased because
there is a lot less turbulence created by the laminar flow. And note,
modern, non-wing paddles can significantly reduce turbulence by slicing
the paddle outwards away from the kayak, just like racers and greenland
paddlers.

Well, the concepts above are quite clear to me, but I wonder how clear it
is to the readers. I suppose I could put it down on a web page, with force
vector diagrams, and with maybe even a bonus picture of me waving my
hands.  Anyhow, I hope my definitions make sense, and maybe clear up a
little confusion. 

Cheers, 
Kevin
	 ___________________                                                            
	/   Kevin Whilden   \
       |Dept. of Geosciences \___
       |University of Washington \
       |kwhilden_at_u.washington.edu| 
        \________________________/                       

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