Thanks for all the suggestions.

You can get more power from the lower body (the muscles are larger) but
for the *same* amount of power the upper body puts more strain on the
heart. That's what I read while researching heart disease.

I have worked before with hull resistance figures for canoes and kayaks.
You can get a pretty good estimate of the horpower required to move a hull
at a certain speed. Non-athlete paddlers can sustain about 1/20 of a
horsepower. It's also easy to calculate the amount of water pumped from
the size of the cylinder and the rate of pumping. It's possible to convert
the amount of foot pressure on the pump into the speed of the water
leaving the pump. I should find out about the efficiency of water pump
propulsion. In one book I was lookign at last night it says the shape of
the outlet nozzel is important. I once estimated the energy comsumption
efficiency of paddling a canoe at about 13% (it's on my website under
"Boats").

I agree with one poster that innovation is the fun part about designing
and bulding boats. But I'm not crazy about the building part,
time-consuming messy physical work costing money, so I try to do as many
calculations as possible before starting to build, even though trying to
figure out the formulae sometimes drives me crazy.

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Foot operated pumps for propulsion don't look practical. They would be too
inefficient and they would only move the boat forward.

The device on the Hobie kayaks is amazing. With all the propulsion under
the hull there is no waste in surface turbulence. However it is
disappointing that it's only 10% more energy efficient than arm
propulsion. I thought it would be less of a strain on the heart. I can
imagine two improvements but don't know if they would be feasible.

First, as the desinger points out, reciprocating leg action is better than
circular leg action, but it would be even better if the action were low
instead of high. Perhaps the cranks could bent over or inverted.

Second, the fins only move the boat forward. If the fins could rotate they
could be aimed in any direction like an outboard motor to steer the boat,
and to propel it backwards.



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