"Martin Baxter" wrote in message
...
Don't leave out the fact that the electric trolling motor power is
produced directly at the prop. There is significant power loss in a
gas outboard between where it is produced and the prop that does the
work.

Hmm, I don't really know, but I don't think the losses should be all that
big, one little water pump to turn, on set of crown and pinion gears.
Intuitively I don't think you'd lose more than 15%..

I'll bet that most outboard manufactures measure output of just the head,
no shaft, no water pump.

It would not be as much as that. 3-5% would be about the right amount.