What’s with the whine from the rear?
QMy boat (with a twin-cylinder watercooled Lister Alpha engine and Centreflex coupling) produces an unpleasant high pitched whining noise (apparently from the stern gland area) at medium revs in forward gear. I have disconnected the coupling and the noise disappears.
There does not seem to be a problem with alignment. Changing the packing makes some difference, particularly if it is not tightened much, but this is only temporary and causes leaks. There is no evidence of wear in the propeller shaft. Is it possible to replace the bronze bearing with the boat in the water? ADRIAN MORTADA, via email
ATONY REPLIES: If it has a hospital silencer and the engine is soundproofed you could be hearing the propeller’s hydrophonic noise which is normally drowned out by engine noise. It could also be a singing propeller (Google ‘singing prop’and follow the instructions for grinding anti-singing edges), or even cavitation.
If the outer shaft was the cause, the noise should go for a while as soon as you use the greaser.
Odd though this sounds, make up a stout wooden plate and fit it in place of the weed hatch temporarily (make sure you secure it properly). If the noise goes away, it is probably vibration causing the lower part of the weed hatch assembly (the anti-cavitation plate) to rub on the trunking. Either get the plate supports strengthened or use an angle grinder to trim the plate to give greater clearance.
I would not try to change any shaft bearings with the boat afloat.
Despite what you say about the shaft being correctly aligned, I would check this carefully before doing much else
Noise may be coming from the anti-cavitation plate