Since I haven't heard of an actual design from anyone, and we have
less than a week left, I'm just going to order some parts to make this
thing work.  I'm also ordering parts for steering.

Proposed design:  a paddlewheel (dimensions and blade count yet
unspecified) of plywood blades.  Pedaler(s) facing astern on some
kind of seats with back support.  Pedals located recumbent-style
off the rear of the vehicle.  Standard bicycle cranks with chainrings.
Chain goes down into water to sprocket on countershaft.  Countershaft
has a gear that meshes with a gear on the paddlewheel shaft to reverse
direction of rotation.  Mounting will take into consideration removal,
waterline adjustment, and maybe chain tensioning.

Questions for discussion:
 - One pedaler or two?
   (Two would likely use separate transmissions to the paddlewheel shaft
   at the waterline, to avoid fabricating a complicated offset pedal shaft.)
 - Overall gear ratio from pedals to paddlewheel?
   (Note that Swan Boats are 1:1 direct drive)

I'm placing the order with McMaster-Carr at lunchtime so it gets here
tomorrow.  So please discuss.  Also note if there is any other crap you
think we may need.

Using a cascade of systematically inaccurate approximations, I have decided
that one cyclist, with great effort, will be able to propel our craft at up
to 3 knots in no wind.

At 3 knots, overcoming frictional resistance would require about 60 watts
of pedaling power.  Unfortunately I cannot predict wave-making resistance,
which is undoubtedly huge for a plow-shaped apparatus like our front
bumper.  Let's guess it is 2x the frictional resistance.  That's 180 watts
to overcome.  Literature suggests transmission efficiency of a properly
designed paddlewheel could be about 50%.  So one cyclist would need to
output approximately 360 watts.  Assuming the gear ratio permits an
efficient cadence, I would call that "moderately rigorous effort."

A headwind of 5 knots would introduce a negligible 12 watt penalty at the
same water speed, but at 10 knots it would increase to a noticable 92 watts
(a liesurely pedaling pace is perhaps 200 watts).

Let's shoot for two sets of pedals if we have time.