"Roger Long" skrev i en meddelelse
...
I'll try.

The answer will be found in conservation of energy. The
energy books have to balance in every system. The amount
if drag of the water flowing over the prop will exactly
equal the energy being produced. With the prop stopped, it
is simply pull aft on the shaft. The prop isn't very
efficient that way. Try propelling a boat by putting the
prop out ahead on a long line and then pulling it in
quickly. When the prop is freewheeling, it is producing
energy that is absorbed by heating up the bearings and
lube oil in the transmission, (or in Larry's case by
charging batteries).

It's slightly counterintuitive but, whatever energy is
produced has to have an exact mirror image in drag on the
boat. Since the prop is making energy more efficiently
while turning, there has to be more drag.

--

Roger Long



Thank you for trying, Roger. Sorry, but I still have some
doubts. In my opinion it requires quite a lot of energy just
to keep the propeller fixed when sailing. It is not
possible - for instance to hold the propeller shaft by
hand - so the shaft does not turn - as Rosalie confirmed ...
So there must be quite a constant pressure on the gear box,
when just sailing and the prop locked by the gearbox. In my
opinion, it could be compared to a kind of turbine, where
you keep the blades fixed from turning ...

My intuition tells me, however, that if you 'let the
propeller go', the total resistance/drag will be less and if
you start braking the turning propeller, the resistance/drag
gets bigger, and that resistance can be converted to
electricity - as explained by Larry -isn't that right? But I
must admit, that I don't know - or may be worse: Don't
understand - the Law of physics behind the right answer ...

--
Flemming Torp

PS - I have followed your interesting 'report' of the last
few months of projects on your boat ... good and inspiring
reading - thank you!