Shaft vibration and scope of work

stevemitchell said:

I am being hauled on Monday for a few things - bottom paint, replacing rudder packing, and probably one or two other small things.

The big job is trying to reduce the vibration in one of the shafts, and vibrations overall. I've owned the boat for about 2 years, and it has always had a bit of vibrations at speeds faster than 11 knots. Slower than that there really hasn't been any issues.

Sometime earlier this year I clipped something with the starboard prop. The vibrations increased quite a bit. I had both props taken off right away starboard was definitely not perfect. I had the shop check both and correct both, although the port one didn't need much.

The vibrations were reduced, but the starboard side is still worse than it was before, I think. It's hard to tell sometimes. Maybe I am just fretting....

I am assuming the cutlass bearing is probably messed up from whatever I hit and the resulting vibrations from the prop that was out of kilter. I will only know for sure once I'm out of the water in the morning.

What I am debating is whether to have the shafts sent out to be trued. It sounds like that could take some time, and I can only have the boat out for 2 weeks max for a number of reasons.

Everyone is busy, and this work was scheduled, but I am wondering if this really will help, or if it is more important to focus on the cutlass bearings, correct engine alignment, etc. Or if there are any other tips or things I should be looking for.

Thanks!

Click to expand...

You may want to have your shaft alignment checked. When you dit something it could have knocked it out of alignment. This can be done while the boat is in the water.
John Welsh

In my experience - mounts and alignment are a dark art

Mounts over 10 years old really should be replaced but it's often difficult to figure out the exact brand/spec used before. You want to get the same hardness of rubber (Durometer). And manufacturers keep making subtle changes. This is why it's also usually necessary to replace all four mounts. The rubber ages and changes it's characteristics. By the way the metal on top of your mount is to keep any oil from dripping on the rubber which destroys it

As to alignment, as someone else noted it mostly takes patience and a refusal to say "good enough". Most boatyard guys who do alignments aren't by nature very patient - and the ones who are are have a boss yelling at them about hours - so they don't try again even though they know it could be done better.

After you have the boat all put back together again do an alignment in the water and run it for 20 hours. The mounts will settle in a bit. If you then aren't happy with the vibration, align again (in the water). I once had to align three times - using two different guys - to get it right.

Steve DAntonio said:

Contrary to popular belief, misalignment, because it is a constant, is rarely the cause of vibration.

Shafts can be checked for trueness, to an extent, without removal. A dial indicator can be placed against the shaft in several locations, and the shaft rotated. It's not as definitive as having the shaft in bench rollers, but it's usually good enough to identify an issue. Run out should be measured at the prop taper end as well as close to the coupling, and in a couple of places in between.

Because you mentioned you had the props checked, if the prop does not fully engage the shaft taper, because it is binding on the key, it will not be perpendicular to the shaft, and will lead to vibration.

If the props were not scanned using Hale MRI or PropScan, they should be, the graphic representation they provide is invaluable in assessing prop condition.

Perhaps above all else, the yard you select for vibration analysis must be knowledgeable and experienced in that realm, those with good intentions can spend a great deal of time, and your money, chasing their proverbial tails in attempting to track down the causes of vibration.

These articles may be helpful...

Cutless Bearings: https://stevedmarineconsulting.com/cutless-bearing-etiquette-2/

Alignment How-To: https://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/

Alignment: https://stevedmarineconsulting.com/wp-content/uploads/2014/03/Shaft-Alignment-159-02.pdf

Prop Installation: https://stevedmarineconsulting.com/propeller-installation/

Click to expand...

Now there is information you can depend on. Steve thanks for the exhaust temp sensor information I found on your web site. Big help on my Eastbay 49.

dbltime said:

Before you haul the boat isolate the source of the vibration. SEA TRIAL Put a tech in the engine room and find out if the wiggle starts at the prop and is running up the shaft
Is the coupling wobbling
Engine alignment is never the cause. Good thing to do to reduce bearing wear but thats it.
Also measure your unsupported shaft between the hull bearing (if you have one) and the strut. You can look up the max unsupported shaft for your diameter on the web.
I have seen heavily damaged props with welded in patches that are not detected unless you use the prop scan

Click to expand...

Thanks for the notes - the boat is already out of the water. The shafts are properly supported for their length as far as we have determined, and the props were MRI scanned and have been brought back to a Class I state.

Keep in mind this was something that started getting worse after a suspected prop strike, not something that has been this way for a long time.

Steve DAntonio said:

Contrary to popular belief, misalignment, because it is a constant, is rarely the cause of vibration.

Shafts can be checked for trueness, to an extent, without removal. A dial indicator can be placed against the shaft in several locations, and the shaft rotated. It's not as definitive as having the shaft in bench rollers, but it's usually good enough to identify an issue. Run out should be measured at the prop taper end as well as close to the coupling, and in a couple of places in between.

Because you mentioned you had the props checked, if the prop does not fully engage the shaft taper, because it is binding on the key, it will not be perpendicular to the shaft, and will lead to vibration.

If the props were not scanned using Hale MRI or PropScan, they should be, the graphic representation they provide is invaluable in assessing prop condition.

Perhaps above all else, the yard you select for vibration analysis must be knowledgeable and experienced in that realm, those with good intentions can spend a great deal of time, and your money, chasing their proverbial tails in attempting to track down the causes of vibration.

These articles may be helpful...

Click to expand...

Hi Steve - I read all of those articles about a month ago before coming to the yard! Your expertise here is invaluable. The yard I selected has two people who are very knowledgeable about everything around shafts, props, alignments, and the related work. They have provided sage advice throughout the process almost in-line with your articles, and I have confidence in their abilities.

The shafts were dialed at multiple points and looked very good. The props were returned to a Class I spec and MRI'ed. Once the shafts go back in (any day now) we'll check the props and how they sit on the shafts for sure.

Since the props were removed, scanned, trued, and replaced by divers 5 weeks or so before the haul, one of the thoughts was whether they were properly re-installed. Nothing was obvious when the boat came out, but we will definitely be checking after things are put back together.

CarlF said:

In my experience - mounts and alignment are a dark art

Mounts over 10 years old really should be replaced but it's often difficult to figure out the exact brand/spec used before. You want to get the same hardness of rubber (Durometer). And manufacturers keep making subtle changes. This is why it's also usually necessary to replace all four mounts. The rubber ages and changes it's characteristics. By the way the metal on top of your mount is to keep any oil from dripping on the rubber which destroys it

As to alignment, as someone else noted it mostly takes patience and a refusal to say "good enough". Most boatyard guys who do alignments aren't by nature very patient - and the ones who are are have a boss yelling at them about hours - so they don't try again even though they know it could be done better.

After you have the boat all put back together again do an alignment in the water and run it for 20 hours. The mounts will settle in a bit. If you then aren't happy with the vibration, align again (in the water). I once had to align three times - using two different guys - to get it right.

Click to expand...

The boat will be in the water for several days before we do an alignment, and the guys working on the boat are excellent. The yard manager (the one that would do the yelling) has background here as well, and knows that it will take time for the alignment, and I'm not worried about it being rushed. The person who will be doing the alignment has done them for 15+ years, and I've seen him work for a number of hours and does not rush things or cut corners.

I do want to replace the mounts later this year, and will likely come back to the yard to have it done water-side given how good they have been through the troubleshooting and work process. I will be replacing all of the mounts all at once.

I have been doing running gear for 30 years i can tell you this whenever running aground be sure to check all of these items;
1. engine mounts 2. engine alignment. 3. coupling to coupling fit should be pinching all the way around 4. check shaft for straightness. 5. check bearing wear 6. check or fix propeller 7. with all running gear is out of vessel and new bearing installed in strut run a wire from center of transmission flange through stern tube , through strut with a gig set up on the end of the wire to verify your strut to engine alignment .

pacemaker69 said:

I have been doing running gear for 30 years i can tell you this whenever running aground be sure to check all of these items;
1. engine mounts 2. engine alignment. 3. coupling to coupling fit should be pinching all the way around 4. check shaft for straightness. 5. check bearing wear 6. check or fix propeller 7. with all running gear is out of vessel and new bearing installed in strut run a wire from center of transmission flange through stern tube , through strut with a gig set up on the end of the wire to verify your strut to engine alignment .

Click to expand...

Thanks for the notes!

To be clear, I didn't run aground. There was a submerged object in a very deep area, most likely a log, that I hit.

1. mounts - being redone in a month or two
2. alignment - being done next week after boat goes back in the water
3. coupling fit - will be examined during the above
4. done - done earlier this week
5. done - minimal
6. done - class I and MRI performed
7. this was done a day or two ago

Hi Steve - I read all of those articles about a month ago before coming to the yard! Your expertise here is invaluable. The yard I selected has two people who are very knowledgeable about everything around shafts, props, alignments, and the related work. They have provided sage advice throughout the process almost in-line with your articles, and I have confidence in their abilities.

The shafts were dialed at multiple points and looked very good. The props were returned to a Class I spec and MRI'ed. Once the shafts go back in (any day now) we'll check the props and how they sit on the shafts for sure.

Since the props were removed, scanned, trued, and replaced by divers 5 weeks or so before the haul, one of the thoughts was whether they were properly re-installed. Nothing was obvious when the boat came out, but we will definitely be checking after things are put back together.



The boat will be in the water for several days before we do an alignment, and the guys working on the boat are excellent. The yard manager (the one that would do the yelling) has background here as well, and knows that it will take time for the alignment, and I'm not worried about it being rushed. The person who will be doing the alignment has done them for 15+ years, and I've seen him work for a number of hours and does not rush things or cut corners.

I do want to replace the mounts later this year, and will likely come back to the yard to have it done water-side given how good they have been through the troubleshooting and work process. I will be replacing all of the mounts all at once.

Click to expand...

Sounds good and like you are in good hands. Props replaced by divers can be problematic, it's just never as good as doing it when hauled, so give that a careful look, and make sure the key isn't binding.

Steve,
Nice to see someone talk nice about a yard in the region. Can I ask which yard it is? Are you using the yards guys or bringing in your own?
Thanks,

Yes. Pull shafts and have them tried. Also consider adding a frangible coupling to save shaft in future events. Some years ago I replaced my 3 blade props with 5 blade. Big vibration reduction. Better speed with same rpm.

For several reasons I'm no fan of "frangible" coupling inserts, which I've detailed on the Forum in the past; they are included here. https://stevedmarineconsulting.com/wp-content/uploads/2019/06/ShaftCouplings179FINAL-PBB.pdf

Not every engine, gear ratio combination that's designed for 4 blade, can support a swap to 5 blade props.

I'm curious, why are you waiting to change the mounts? You will be duplicating some of the work, especially alignment.

Steve DAntonio said:

For several reasons I'm no fan of "frangible" coupling inserts, which I've detailed on the Forum in the past; they are included here. https://stevedmarineconsulting.com/wp-content/uploads/2019/06/ShaftCouplings179FINAL-PBB.pdf

Not every engine, gear ratio combination that's designed for 4 blade, can support a swap to 5 blade props.

I'm curious, why are you waiting to change the mounts? You will be duplicating some of the work, especially alignment.

Click to expand...

I had read about coupling inserts, and one of your articles on them, and I won't be adding them.

I would love to replace the engine mounts now, but due to the yard schedule I would have to wait out on the hard for a couple of weeks with no actual work being done. Since I live aboard, that's expensive and really quite a problem - living in a hotel is really not that fun right now with everything going on in the world.

Most yards right now in the area are booked out 4-6 weeks if not longer. The one I'm at can definitely do the work, they just didn't expect to have to do this particular work, and they have staff shortages as well due to COVID.

I know it will require another alignment, but that's OK - when they have time we can do it from the water including the replacement.