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Old 15-06-2016, 12:28   #1
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Vibration troubleshooting help

Hi there,

I have noticed there is vibration when the boat is in gear under motor. It is more noticeable at certain revs. It has gotten progressively worse in the past few months.

I had the stern gland and cutless bearing changed when I bought the boat about a year ago.

Today I had a mechanic check things out. He identified that there is a space between the propellor shaft and the cutless bearing. Which he says indicates the shaft is not in line.

What are your thoughts?

I will try to upload a photo. I can clearly see the gap.


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Old 15-06-2016, 12:35   #2
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Re: Vibration troubleshooting help

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Old 15-06-2016, 12:57   #3
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Re: Vibration troubleshooting help

Is there excessive leaking? It is very possible that if a barring has failed or the prop shaft is not aligned you can have excessive vibration. Additionally, when is the last time you looked at the prop itself? Is it clean?
I've seen misaligned shafts with little or no vibration.... how much is your shaking?
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Old 15-06-2016, 12:59   #4
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Re: Vibration troubleshooting help

The photo is from inside so it should be stuffing box but looks a bit odd. Is your boat on the hard or was the mech diving to see the cutlass bearing? If the shaft is not bend then it might be the engine mounts loosed or something related.

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Old 15-06-2016, 13:53   #5
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Re: Vibration troubleshooting help

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Originally Posted by TeddyDiver View Post
The photo is from inside so it should be stuffing box but looks a bit odd. Is your boat on the hard or was the mech diving to see the cutlass bearing? If the shaft is not bend then it might be the engine mounts loosed or something related.

BR Teddy
Hey there, the boat is in the water. The photo is taken from the inside. The camera was positioned under the shaft.

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Old 15-06-2016, 13:58   #6
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Re: Vibration troubleshooting help

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Originally Posted by ad-ventureout View Post
Is there excessive leaking? It is very possible that if a barring has failed or the prop shaft is not aligned you can have excessive vibration. Additionally, when is the last time you looked at the prop itself? Is it clean?
I've seen misaligned shafts with little or no vibration.... how much is your shaking?
I don't know what excessive is. It does drip when the shaft is rotating but not much. The prop is very clean. I look at it daily as I am swimming. The prop has a tiny ding or knick in the edge of one of the blades. That is all I could fault.

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Old 15-06-2016, 14:42   #7
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Re: Vibration troubleshooting help

If you placed a glass half full of water somewhere on your boat, would the vibrations splash the water around enough where you would loss water from the glass? I know, sounds like an algebra questions. If so, I would consider that extreme excessive vibration.
Without seeing more, I would 'guess' that a barring went bad. I have seen more misaligned props with less vibration that what it seems you are talking about. If the barring is bad, or even the wrong size/sticking, you can get vibration. Have you had the boat in gear while you look at the shaft? If not, please be mindful of your fingers while you look.
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Old 15-06-2016, 14:52   #8
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Re: Vibration troubleshooting help

Hard to see but it may be out of alignment. Try aligning it!
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Old 15-06-2016, 14:52   #9
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Re: Vibration troubleshooting help

I think if I filled a glass to with 1cm of the rim I might lose a little water if I held it firmly against the floor of the cockpit. I am speculating though.

I have looked at the shaft while in gear and even felt with my finger against it. There is a vibration. But how to covey how much is very difficult. I might be overly sensetive. But what I do know is the vibrations are getting worse. For example in tick over forward the swinging chart plotter holder is rattling and this is a new thing.

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Old 15-06-2016, 14:55   #10
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Re: Vibration troubleshooting help

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Hard to see but it may be out of alignment. Try aligning it!
I want to be sure of the problem before I spend 1500 EUR

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Old 15-06-2016, 14:55   #11
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Re: Vibration troubleshooting help

I would start with realigning it before taking it apart to look at the barring. That would be the cheaper of the two options.
If you get more info let us know!
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Old 15-06-2016, 15:33   #12
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Re: Vibration troubleshooting help

On my boat I just finished replacing the cutlass (very worn), the shaft log (worn out where prop shaft had contacted it due to mis-alignment) and stuffing box, as well as engine rubber mounts.

I also had a vibration problem. Could have been the cutlass, but the shaft was also contacting the stainless shaft log (it was also corroded and had a slow leak), which could have caused vibrations.

To test you cutlass, grab the prop and shake it up and down and sideways to test for cutlass play. It should be tight or just have very minor play. It does look like you shaft is hitting the edge of what looks like a stuffing box or dripless shaft seal. As others have said, check your engine mounts and then do an alignment. The shaft should be aligned so that it is centered in the shaft log (cutlass strut needs to be correct for this to happen- hopefully it is), then the engine coupling needs to be aligned with the shaft coupling. The couplings need to be parallel and centered.

What is the shaft log in the pic?
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Old 15-06-2016, 15:39   #13
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Re: Vibration troubleshooting help

It would be worth checking the condition of your engine mounts. That is often the cause of vibration problems. They may be starting to sag and a small adjustment may get rid of your vibration.

Here is a good article to read. Marine Engines : Drive System Alignment by David Pascoe, Marine Surveyor
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Old 15-06-2016, 16:25   #14
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Re: Vibration troubleshooting help

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Originally Posted by F10 View Post
On my boat I just finished replacing the cutlass (very worn), the shaft log (worn out where prop shaft had contacted it due to mis-alignment) and stuffing box, as well as engine rubber mounts.

I also had a vibration problem. Could have been the cutlass, but the shaft was also contacting the stainless shaft log (it was also corroded and had a slow leak), which could have caused vibrations.

To test you cutlass, grab the prop and shake it up and down and sideways to test for cutlass play. It should be tight or just have very minor play. It does look like you shaft is hitting the edge of what looks like a stuffing box or dripless shaft seal. As others have said, check your engine mounts and then do an alignment. The shaft should be aligned so that it is centered in the shaft log (cutlass strut needs to be correct for this to happen- hopefully it is), then the engine coupling needs to be aligned with the shaft coupling. The couplings need to be parallel and centered.

What is the shaft log in the pic?
Thanks. I replaced the cutlass and drip less shaft seal in October last year. There is very little play when I try to shake the prop.
I do not understand your last question about the shaft log.


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Old 15-06-2016, 16:30   #15
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Re: Vibration troubleshooting help

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Originally Posted by Kokanee View Post
It would be worth checking the condition of your engine mounts. That is often the cause of vibration problems. They may be starting to sag and a small adjustment may get rid of your vibration.

Here is a good article to read. Marine Engines : Drive System Alignment by David Pascoe, Marine Surveyor
Thanks. The mechanic did a visual inspection of the mounts and said they looked fine. How does one know for sure? I did call the Yanmar dealer that did the last service and they said the mounts should last many years (much more than they are old). They are from 2008 with about 900 hours on them.

One other thing. If they had started to sag I would expect the gap to be at the top of the shaft and not the bottom like it is. It appears that the engine should be lowered to correct the angle.

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