[Paddlewise] Newtonian Physics

To paraphrase a famous joke about physicists,
"Assume the paddle is a sphere . . ."

Seriously, the physics does not need to be all that complicated
to provide some insight. A reasonable question to ask is how
much power does the paddler have to put out for a given
boat speed.  The equation for power is simply:

POWER = FORCE * VELOCITY

The FORCE is just the resistance of the boat at that
speed, becasue of the constant speed assumption.
You can look up the resistance numbers in Sea Kayaker. (I am
ignoring the effects of "coasting" between strokes.)

The VELOCITY is the velocity of the paddle relative to the
paddler, which is the velocity of the boat through the
water PLUS the velociy of the paddle through the water, i.e.
the speed of paddle slippage.

Thus, the power that a paddler has to put in to keep
a constant boat speed is equal to:

     BOAT_RESISTANCE * (BOAT_SPEED + PADDLE_SLIPPAGE_SPEED)

In other words, all other things being equal, greater slippage
means more power output by the paddler with no speed advantage.
Note that this has nothing to do with paddle shape, except in
how much slippage the shape allows.  A giant pine cone would
work fine as a paddle, except that it would be hard to pull it
out of the water after every stroke.

Peter Chopelas wrote:
>  efficiency of converting power-in to forward movement:   0.001279/0.025 = 
>0.051 or about 5 percent

Efficiency of 5% would mean that for a boat speed of 3knots,
the paddle is slipping backwards at 57 knots, something none
of us have experienced.

Jeff Steck

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