On Tue, 23 Nov 2010 06:15:07 -0500, Wayne.B
wrote:

On Tue, 23 Nov 2010 17:46:50 +0700, Bruce
wrote:

Out of curiosity, why chain the shaft? Are you running on one engine?
And, if you are how is it working for you. I tried it and it simply
dropped the speed by about half :-(

On our boat we can improve fuel efficiency by about 25% running on a
single engine assuming a speed of no more than about 1.1 SQRT LWL.

We have Detroit 6-71 2-cycle diesels which are not efficient at low
speeds. Running single engine gets operating RPMs up to a normal
level. This is useful on long passages in relatively light winds and
calm seas. If the wind kicks up we need more power to maintain speed
and stability.

Tough finding a solution to that.
Just a few thing things that popped into my head, probably none
practical.
Re-propping to get revs up on both engines - non-starter because
you're running 2 engines, and waste heat kills fuel savings.
Transmission that can run both props on one engine input.
Makes sense for cruising speed, but probably too expensive/complex.
Feathering props. Probably more drawbacks than gain.
Easily detached props. Read to dive far asea, hoist, and get caught
with only one prop when it squalls? Didn't think so.
My favorite lame-brain idea is streamlined remote operated prop cowls.
Close when prop not in use, open otherwise.
Insane.

Do you have trans lube/heat problems when freewheeling a prop?
If you lock it down, will you still get 25% fuel savings?
Lots of drag there.

--Vic