gearbox 'droning' sound while sailing

[jarwin]

Hi and good morning. We have a 1997 Beneteau 36cc from new with a Volvo Penta 2040 diesel inboard engine and a fixed 15" prop and live and sail in the Middle East. We sail with a free spinning prop with gearbox in neutral. Last Thursday, sailing at 7 knots, a loud 'droning' sound started to come from the gearbox a which was hot to touch. Reducing speed to 4 knots and the 'droning' sound stopped. We recently fitted a new prop shaft seal and cutlass bearing and the shaft is stiffer to rotate by hand than before. We have greased and vented the seal. Any thoughts, please?

 

[DougM]

I was always told to put the transmission in reverse to prevent the propeller from freewheeling. This supposedly is done to keep the gearbox from overheating. Check the fluid level in your gearbox as well, it may be running dry... not a good thing.

I know that there are contrary opinions, and you will probably see a few of them on this site.

 

[xavierlh1]

Putting the boat in reverse will certainly cut the noise of the free-wheeling prop under sail (whether the normal noise, or Jarwin's new droning sound. People do it for a variety of reasons:
. Cutting down on mechanical noise when sailing peacefully.
. Cutting down on wear and tear for the transmission.
. Slowing down the boat ! We've actually done that when buddy boating with a slower boat.

I never conclusive evidence that putting the boat in reverse improves the lifetime of a transmission. On the other hand there are days when I can't stand that small background noise, but can't bear the thought of loosing close to one knot!

Who can cut this Gordian Knot?