Unpleasant noises when going astern?

[bumblefish]

On a friends's Moody today, no problem going ahead and idling astern is fine. However, as soon as there is any load astern there is an awful noise apparently coming from the stern gland. Quick look and there did not appear to be anything on the prop. Any thoughts?

 

[tcm]

i reckon that there IS summink on the prop. Dya give it a run forwards and backwards?

 

[ShipsWoofy]

Is it a new sound or a new boat so you don't know?

It could be that the cutlass bearing is at the end of its life and allowing too much vibration, strange it only happens in reverse though.

Ditto with gland packing or grease, did he grease up prior to launch.

Another scenario and not a good one, it could be the the thrust bearing wearing away and showing when the shaft is trying to pull out of the back of the boat.

Just thinking alloud.....

 

[gibbo26]

Could be a loose shaft anode if its hitting the hull, gets pushed up shaft by the prop wash!

 

[rwakeham]

I had the same last season - was the cutlass bearing and had to haul out and replace.

 

[Das_Boot]

When going astearn your propellor is trying to pull away from the boat when going forward it is trying to push into the boat.
This causes differing loads on the shaft bearings etc.
Because it sounds ok going forward and in neutral it seems that it might be at the coupling as the loads should be similar in any direction at the bearings.

 

[snowleopard]

do you have a thrust bearing?

it sounds like end-float in the shaft. try sliding the shaft in and out with the engine stopped, you may find that it moves more than it should.

 

[scottb34300]

Hi, check the andoe. That has solved this problem for me before.

 

[Benbow]

I agree and would bet on a rattling shaft anode if it started suddenly. If it has been slowly getting more noticable then it is one of the more expensive posibilities mentioned above.

 

[SimonD]

I had the same. Nasty grinding noise which gradually went away if I persisted in drive. No vibration, not obviously coming from the gearbox, nearly new cutlass bearing. Then I read somewhere that fouling on the shaft in the cutlass bearing can cause this sort of noise.

Over the winter I disconnected the prophaft flange to slide it back and there was some that white, calcified looking fouling you tend on get on the shaft right inside the bearing. Carefully scraped it out. Don't know if it's worked yet, but perhaps worth a look.

Simon

 

[Das_Boot]

Another thing I forgot was that the loads on the bearings do differ. Because of the direction the prop is moving there would be slightly more load on the side depending on the direction so it could be bearings.
If it is something touching the shaft or propellor it should make a noise whenever it turns in whichever direction.

 

[bumblefish]

So far we have tried repacking the stern gland, apparently very very dry, and it may have made a difference, Lord knows why! Will try and get out later this afternoon and give it some stick, whether we can sail into or out of Brighton Marina in the event of engine failure is another matter. Thanks for all the suggestions and help.