On Sat, 20 Nov 2010 21:18:30 -0500, Wayne.B
wrote:

On Sun, 21 Nov 2010 07:19:02 +0700, Bruce
wrote:

Frankly it sounds very much like a perpetual motion machine.

It's definitely not perpetual motion but it does depend on a number of
assumptions that may not hold true in the real world. Extracting
energy from spinning props is definitely possible under the right
conditions but my calculations show that the maximum power available
is relatively low, quite possibly enough to supply house loads, but
very unlikely enough to recharge a large battery bank.


I knew one person who had a propeller shaft driven alternator on a 40
ft. sloop and metered it's output. He said that it produced
electricity but not much and removed it to install a propshaft driven
bilge pump - bloody great thing it was. I used to offer to chop a hole
in the hole so he could test it but he never seemed to be interested.

A second had one of those towed generators and said much the same - it
did produce electricity but he still needed to run the engine
frequently when sailing unless he was very, very careful with the
electricity. He had a vane steerer so the only "can't turn it off" he
had running would have been his GPS and maybe his nav lights, but I
doubt that he would use them off shore.

And these were blokes who did sail off shore - used to quote speed in
miles per day :-) Along shore I think it would be worse. Hopefully
anyone who tries this system keeps a big outboard on board :-(

Cheers,

Brice