[Paddlewise] Biomechanics

 > What is more difficult are the
>biomechanical losses.

John,

Please comment, if you have time, on the following:

Every motor has a torque-speed curve.  At max torque, speed is zero, and
therefore power is also zero.  Likewise at max speed, torque is zero, and
therefore power is again zero.  Max power occurs somewhere in between.  It
is important to note that max efficiency does not generally occur at the
speed for max power.

In a kayak, the paddler is the motor.  Changing the length of the paddle or
the shape of the blade will change the point on the paddler's torque-speed
curve.  Every paddler has a different curve and must choose a paddle design
that gives him either optimal power or optimal efficiency.  Probably, a
different design for each objective.

With my 57 year old body, a long narrow paddle is most efficient over long
distance.  I stroke low, with relaxed shoulders and slow cadence, while
getting most power from lower torso.   I try to emulate the Greenland stroke
taught by VanDoren in his video, but more slowly.  On occasions (very rare)
when I try to race a short distance  (less than 1 mile),  a shorter paddle
with big blades and high stroke lets me get my shoulders into it and I can
reach greater speed, but at a big cost in effort.

I think that the significant energy loss in paddling is biomechanical,
rather than losses due to inefficiencies in the paddle blade/ water
interaction.  (Assuming constant loss due to boat drag.)  Further,  the drag
coefficient always appears multiplied by the area (I think), CdA.  For a
given Cd one does not necessarily want a larger A.  Similarly, for a given A
one does not necessarily want a larger Cd.  Both move one to a different
point on the torque-speed curve.

It seems to me that the implication is that efficiency is not a property
that is inherent to a particular paddle, but whether that paddle and the
appropriate corresponding technique is matched to the paddler.

Jerry



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