On Wed, 20 May 2015 13:43:02 -0500, Boating All Out
wrote:

In article ,
says...


I have done controlled tests with our boat, running slowly at around 7
kts on a single engine, and letting the idle prop spin freely. The
fuel save was 20% at best.

That's a significant savings. Since you didn't lock down the idling
shaft, what are the downsides?

===

The most significant downside is possible damage to the transmission.
On a boat with no crossover cooling water to the shaft log, it and the
cutlass bearing are also at risk.

On my boat we have active fin (Naiad) stabilizers which minimize
rolling in heavy seas. They are much less effective at slower speeds
so that is a secondary draw back.