Vibration

[oak]

I have a 2007 Pilot34 was curious is any has had vibration issues and changed the prop from what I believe the original 25R28 Lcuptip to something else. If so did it help?

 

[DavidM]

I have a very mild cavitation, not vibration I think, on my 2003 Pilot 34. It seems to relate to wave action and it comes and goes. More of a sound rather than a vibration. I tried fairing the area where the prop shaft comes out, but no help.

Do you have real vibration? Put a cup of water, coffee, ??? on the engine block while idling up at 1,000. Does it really wiggle or just a little ripples. Look at the prop shaft also at 1,000 in gear. Does it run true with very little, maybe a few thousandth of an inch out of true?

If either of these problems are visible then in the approximate order of probability and ease of checking:

Engine/shaft alignment
Prop dinged, bent
Prop not seated on taper, seated on key
Prop coupling faces not square to shaft
Prop shaft bent
Engine mounts worn- rather unlikely I think

For the engine shaking in addition to some of the above, a bad injector not firing will also cause this.

David

 

[Delfin]

I have a very mild cavitation, not vibration I think, on my 2003 Pilot 34. It seems to relate to wave action and it comes and goes. More of a sound rather than a vibration. I tried fairing the area where the prop shaft comes out, but no help.

Do you have real vibration? Put a cup of water, coffee, ??? on the engine block while idling up at 1,000. Does it really wiggle or just a little ripples. Look at the prop shaft also at 1,000 in gear. Does it run true with very little, maybe a few thousandth of an inch out of true?

If either of these problems are visible then in the approximate order of probability and ease of checking:

Engine/shaft alignment
Prop dinged, bent
Prop not seated on taper, seated on key
Prop coupling faces not square to shaft
Prop shaft bent
Engine mounts worn- rather unlikely I think

For the engine shaking in addition to some of the above, a bad injector not firing will also cause this.

David

I would add to that a worn cutlass bearing. That is a very common source of vibration, especially on longer shafts. Easy to check as well.

 

[oak]

I have a very mild cavitation, not vibration I think, on my 2003 Pilot 34. It seems to relate to wave action and it comes and goes. More of a sound rather than a vibration. I tried fairing the area where the prop shaft comes out, but no help.

Do you have real vibration? Put a cup of water, coffee, ??? on the engine block while idling up at 1,000. Does it really wiggle or just a little ripples. Look at the prop shaft also at 1,000 in gear. Does it run true with very little, maybe a few thousandth of an inch out of true?

If either of these problems are visible then in the approximate order of probability and ease of checking:

Engine/shaft alignment
Prop dinged, bent
Prop not seated on taper, seated on key
Prop coupling faces not square to shaft
Prop shaft bent
Engine mounts worn- rather unlikely I think

For the engine shaking in addition to some of the above, a bad injector not firing will also cause this.

David

The engine idles smoothly in neutral at all rpm.
The vibration seems to begin at high rpm while underway. It is most pronounced at about 2800rpm. It is intermittent varying from no vibration to a loud rumbling that can be heard and felt.
I purchased the boat in June of 2016, she was perfect at sea trial and for about 10 months. At that time I began to get the vibration. I had the shaft, prop checked, changed the cutlass bearing, engine aligned and replaced rear motor mounts. After all of that boat ran fine for about 9 months and then vibration returned. After returning for the second time I had diver clean and check running gear below water.then I ran boat and noticed an improvement , maybe 40% better but still 60%not good.
I am waiting for the diver to inspect the prop for imperfections and tightness and also the cutlass bearing.
In my 19years of sailing and 10 with a trawler I have never had a vibration issue. But in spite of this issue I think it’s a great boat. In the times she was running well we had several very enjoyable cruises here in South East Florida.
Appreciate the input

 

[DavidM]

I think you have a cavitation problem. Mine also worsens with a slightly fouled prop and is not really noticeable with a clean prop and bottom.

Talk to a good prop shop. Cavitation can sometimes be resolved with cup on the prop. Mine came from the factory with a slight cup and I haven't done anything to it other than get it scanned and trued to Class 1.

David

 

[LaBomba]

Having worked in power houses for many years there is a thing we refer to as critical speeds. On one turbine generator set I worked with the criticals were at 1800 and 3100 and the turbine eventually was run at 3600 rpm. The turbine generator when reaching the critical speed would be moved through these speeds quickly to avoid vibration and possible damage if excessive. Although not entirely the same, all rotating equipment sets up deflections at certain speeds. So one solution is simply to avoid speeds that cause vibrations. To better understand this, here is a read on Critical Speeds, marine. May or may not be a solution for you, but may be of interest nonetheless.

https://www.marineinsight.com/naval-architecture/types-of-vibrations-on-ships-machinery-vibrations/

 

[oak]

David can you describe what cavitation sounds and feels like.
Do you know what cup your prop is mine is 25R28 Lcup tip.
Do you have the same original factory installed prop?

 

[oak]

Thank you for the helpful responses
Does anyone know how to tell if vibration is cavitation or mechanical issues. Do they sound or feel different?

 

[DavidM]

Like I said, what I think is cavitation is more of a grinding sound than a vibration that comes and goes as you punch through waves. It is almost un-noticeable with a clean bottom and prop, but increases as the prop gets fouled a bit. Even when fouled it is still light at 2,800 rpm and gets very noticeable at wot.

I have the factory prop, can't remember the size, with what the prop guy said was a light cup.

David

 

[oak]

Mystery vibration issue solved.
Sometimes the simple things are overlooked
Had my diver come and thoroughly clean bottom and check the shaft, prop and bearing. All was good except the zinc was gone. Installed a new shaft zinc.
Ran the boat and it ran perfectly no vibration.
So thinking the worn shaft zinc made the shaft unbalanced or that it caused a disturbance in the water flow and cavitation.
Either way issue is resolved.
Thank all for your help

 

[Ski in NC]

Dirty props/shafts/rudder/bottom can cause lots more vibe and noise. That's one way I know it time to dive and clean. Only water is too cold for my liking for about a month!!!

 

[GoneFarrell]

Oak,

Very interesting! Thanks for the update. I remember that my boat was smooth as silk after bottom & prop cleaning with new shaft zincs.

Did your diver place the shaft zinc close to the strut or about halfway back, any idea?

 

[oak]

The zinc is placed about 1/2 way between the bearing and prop.
Wonder if it would be better closer to bearing or prop?

 

[Comodave]

No, you don’t want it too close to the bearing or it may starve the bearing of cooling water flow. It should be a few inches forward at least.