Couple of hours a day, at 10 amps? Compared to an engine charging at
30 amps? Free excercise?

With an electric motor / generator, you could charge batteries or
direct drive, emulate rowing, even use solar power. You could also
charge from the prop under sail. A direct pedal drive might work more
efficiently, if geared in after the engine drive. A wind generator
could also contribute.

If a man can row across the ocean, why not pedal / sail? Drag a krill
net an hour a day and get plenty of food. Catch rain to drink.

Be the first new independant sustainable aquatic mammal life form in
millions of years? Let Darwin be your judge.

Terry K