Significant Propeller Shaft Vibration

[Stasis]

I have an '85 Wellington 57 motor cruiser with a single prop. It hadn't been run for about 5 months and did not have any issues last cruise. This weekend I started it up just to run it a little in the slip, when I engaged the prop I encountered heavy vibration which wasn't there at all last time it was out. I checked out the prop, cleaned any sea life off of it, and spun the prop by hand. When spinning the prop it would vibrate and at times you would see the shaft shake a little. Below is a video of this, watch with audio on. I checked the linkage, all looked good. Is this likely a failed cutlass, or any other suggestions? Thanks all!


https://youtu.be/oinlGlcYGaY

[C420sailor]

It’s really hard to tell, but it looks to me like a worn cutlass bearing is allowing the shaft to chatter around in there, causing that low frequency noise. Any radial play?

[Stasis]

Originally Posted by C420sailor

It’s really hard to tell, but it looks to me like a worn cutlass bearing is allowing the shaft to chatter around in there, causing that low frequency noise. Any radial play?

It felt like there was some but was difficult to tell while diving.

[skipperpete]

There is occasionally a serious shaft chatter/vibration condition caused by a hard layer of marine growth on the prop shaft right up into the stern tube and if the shaft is sitting in a cutlass rubber bearing the growth is only on the areas of the shaft NOT in contact with the rubber flutes. The growth is similar to 80 grit sandpaper and because of the gaps in the coverage causes a helluva noise. The fix is easy..... undo the gearbox coupling, slide the shaft aft and carefully remove the abrasive crust with a tool of your choice..... sometimes it shatters and falls off if tapped lightly with a small steel hammer.
This is a fairly common shaft/bearing issue.
Pete.

[EWOL Props]

Vibration can depend on multiple things: prop unbalancing due to corrosion or damaged blades, fouling, bent or mis-aligned shaft, worn out cutlass rubber bearing, damaged silent blocks.
I'd suggest to check all of those aspects

[Stasis]

Originally Posted by EWOL Props

Vibration can depend on multiple things: prop unbalancing due to corrosion or damaged blades, fouling, bent or mis-aligned shaft, worn out cutlass rubber bearing, damaged silent blocks.
I'd suggest to check all of those aspects

The prop is not damaged and I cleaned off any sea life but still have the vibration issue. And I wouldn't think I'd get the vibration and shaft shaking when just slowly spinning the prop by hand if it was simply something to do with the prop. The boat was in the yard 5 months ago and had none of these issues on the return trip. It is a fairly large shaft, and hadn't hit anything since it was running fine, so I don't believe it's a bent shaft. Not sure what silent blocks are or if I have any? So I am thinking cutlass bearing or it somehow came out of alignment. Would it need to be aligned after replacing the cutlass? Seems that is the route I need to take.

[sail sfbay]

Suggest checking motor alignment. I had a new shaft go out of alignment on a powerboat, resulting in vibration above 1000 rpm. The fix was to install motor mount shims.

[BillKny]

On more thing to check... the connection at the coupling between the transmission and shaft. If any part of that assembly is loose it could cause such symptoms.

[Clivevon]

Check your engine mounts for possible deterioration (softness) causing shaft misalignment. Also check your shaft to transmission bolts.

[Cadence]

Originally Posted by Stasis

The prop is not damaged and I cleaned off any sea life but still have the vibration issue. And I wouldn't think I'd get the vibration and shaft shaking when just slowly spinning the prop by hand if it was simply something to do with the prop. The boat was in the yard 5 months ago and had none of these issues on the return trip. It is a fairly large shaft, and hadn't hit anything since it was running fine, so I don't believe it's a bent shaft. Not sure what silent blocks are or if I have any? So I am thinking cutlass bearing or it somehow came out of alignment. Would it need to be aligned after replacing the cutlass? Seems that is the route I need to take.

My guess if she sat that long you have growth in the cutless grooves. Try snaking them out with a stiff wire.

[GordMay]

Originally Posted by Clivevon

Check your engine mounts for possible deterioration (softness) causing shaft misalignment. Also check your shaft to transmission bolts.

If the engine vibrates when it is running, with transmission in neutral, you may have worn engine mounts (aka: 'silent blocks').

[Squanderbucks]

Eyeballing these things is only good for a quick survey for which place to start.
Very few vibrations can be fully diagnosed by eye. Shaft and coupler have to be checked by feeler gauges with just a few 3 or at most 5 thousandths off is too much. You can’t see that spinning by hand.
Bad mounts can sometimes be seen. But when new ones are fitted you still have to do the whole 9 yards to align. You can’t just fit “exact” replacements and bolt them in and good to go.
Struts can be loose or bent if your boat has one.
Shaft can be bent but you would normally diagnose that out of the water with a dial indicator at the end of the prop shaft while turning by hand.
No matter - significant vibration you describe is not trivial and can lead to severe damage to transmission or loss of prop when taper or key fails.
Diagnosing cutlass bearing can be done by eye-feel but having the knowledge to know how much play is ok is the issue. Should definitely not feel any side to side clunk. They allowable play us very subtle especially when trying to diagnose in the water. Easier when grabbing the prop and shaking. Not so easy inside the boat.

[Stasis]

Originally Posted by GordMay

If the engine vibrates when it is running, with transmission in neutral, you may have worn engine mounts (aka: 'silent blocks').

Everything seems fine when the engine is running, it is only when I engage the prop.

[Stasis]

Originally Posted by BillKny

On more thing to check... the connection at the coupling between the transmission and shaft. If any part of that assembly is loose it could cause such symptoms.

Everything is tight and looks good there.

[Stasis]

Originally Posted by Cadence

My guess if she sat that long you have growth in the cutless grooves. Try snaking them out with a stiff wire.

The boat is in the Keys and it typically doesn't build up much growth over that amount of time. You would just poke a wire in there? Or use some kind of wire brush?