Singing gearbox

[Pelican]

On cruising around yesterday I noticed a singing or moaning noise from the gearbox of my 32 year old MD2B. The oil level - which is the same as the engine is OK. The engine was rebuilt a few months back and to stop some vibrations in the drive a Vetus flexible coupling was fitted. Could it be that this coupling is putting a strain on the gearbox? When I speed up the moaning goes away, when I slow down it come and goes. Any suggestions of what the noise could be are very welcome!! Many thanks!
Pelican

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[jleaworthy]

Are you sure it's a singing gearbox rather than a singing propeller? If you have had any changes to the latter or damage it's a possibility as it can make a very worrying noise! A singing propeller is caused by vortices being shed from the blunt trailing edges of the propeller blades. A little attention from a fine file is usually all that is needed in fining down those trailing edges.

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[Pelican]

Thank you Jleaworthy - your suggestion brings some thoughts to mind! As the Swiss lower the level of lake Geneva every 4 winters (or leap years - so that owners of harbours/ jetties etc can do maintenance work etc) I have had the odd encounter with mooring chains. My boat has a long keel and the propellor is protected by the keel - so I never deviate from my course just for a few fishermen nets/chains on account of this! I will check this and let you know- many thanks
Pelican

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