inboard rythmic vibration

[1kwik72]

I'm looking at a Wellcraft 31 Express with 454 V drives. The motors run great, transmissions shift smooth etc. But there is a rythmic vibration at cruise power that is bad enough to feel in the helm. The current owner says it's in the hydraulic steering, but it only does it at cruise power 2K RPMs and up and it's frequency coinides with rpm. Any ideas what's wrong?

 

[arks]

Re: inboard rythmic vibration

Possibly a bent shaft, damaged prop, or worn strut bearing.
Have it checked by a professional because any of them can be expensive to fix.

 

[jtmarten]

Re: inboard rythmic vibration

Run each side separately determine which side has the vibration. Could be harmonics from the engines being out of sync too.

 

[1kwik72]

Re: inboard rythmic vibration

good idea on running each side to see which one it's coming from. I know it's not the engine sync because it's more severe than harmonics.

How do I diagnose damaged strut bearing or bent prop shaft. At idle or below roughly 2K rpm its smooth as silk.

 

[Lyle29464]

Re: inboard rythmic vibration

If you cant pull the boat I would have a diver check it with a dial indicator

 

[1kwik72]

Re: inboard rythmic vibration

I'll have to see what the current owner wants to do to check this out.

 

[1kwik72]

Re: inboard rythmic vibration

He's going to fix whatever the vibration is now...thanks for the input!