Shaft vibration and scope of work

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!

The shaft may be bent. I would check the cutlass bearings, they make plastic feeler gauges so you can check the clearance. Also just try shaking it side to side and see if there is much play. Use the good shaft for reference. More likely the shaft got bent. It could even be the engine alignment. You can check it before you haul, not on the hard as alignment may change out of the water. I would probably check it before the haul as it is quick and easy and may save the haul.

How do you check the alignment in the water?

I need new bottom paint anyhow, so I have to be hauled.

I was planning on checking play of the cutlass bearings after haul - usually if they’re really bad you can move it by hand.

Basically you get feeler gauge and then loosen the bolts on the prop shaft coupler and check that the clearance is the same within the tolerances between the 12 oclock and 6 oclock positions. Then the 3 oclock and 9 oclock positions. If you have a 6” prop shaft coupler you are allowed up to 6 thousands different top to bottom or side to side. It they are more than the allowable then you have to adjust the motor mounts to move the engine so it aligns with the prop shaft. That is the only difficult part, figuring which mount to adjust and which way to adjust it. But doing the check is really easy and if it is out maybe then get a mechanic to do the adjustment. Checking should be able to do in about 15 minutes or so. But you don’t want to do it on the hard as the boat can get out of shape and throw off the alignment. If you do it after the haul out wait a couple of days for the hull to relax back to it’s normal shape before doing the alignment. Good luck.

Sounds like you have all the bases covered. You should be able to use a dial indicator to check runout. In my opinion any bottom contact that would bend a shaft would trash your props.

Bearing wear is normal and shafts would have to be pulled to replace them. Any up or down movement is signal for replacement. Back and forth movement would lead you to transmission.

Engine alignment is another area to explore. You should be able to get it within .002-.003 if you're patient. Alignment assumes the mounts are in good condition and of proper hardness. Run engine at the vibration rpm, check each mount for excessive vibration.

Typically most drivetrain issues will vibrate at all speeds. Were your props scanned? If they were certified to Class III, pitch deviation of +/- 4% for each blade is allowed. You might want to have them tuned to a higher Class.

Comodave said:

Basically you get feeler gauge and then loosen the bolts on the prop shaft coupler and check that the clearance is the same within the tolerances between the 12 oclock and 6 oclock positions. Then the 3 oclock and 9 oclock positions. If you have a 6” prop shaft coupler you are allowed up to 6 thousands different top to bottom or side to side. It they are more than the allowable then you have to adjust the motor mounts to move the engine so it aligns with the prop shaft. That is the only difficult part, figuring which mount to adjust and which way to adjust it. But doing the check is really easy and if it is out maybe then get a mechanic to do the adjustment. Checking should be able to do in about 15 minutes or so. But you don’t want to do it on the hard as the boat can get out of shape and throw off the alignment. If you do it after the haul out wait a couple of days for the hull to relax back to it’s normal shape before doing the alignment. Good luck.

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Gotcha - so doing an engine alignment in the water prior to haul out could be a way of telling what’s wrong or at least gathering some more data. Good point.

In my time I worked in yards and owned a yard. Usually when a yacht damages a prop it bends the shaft a little, too. Most yacht builders put in the smallest shaft they can get away with. Sometimes the strut gets out of alignment, too. Especially in grounding where the boat weight gets put on the strut.
It's worth the time to check the strut and shaft rather than find you still have a vibration when you're back in the water.

See attached

FYI, our 44 OA has three cutless bearings per shaft....one (composite shell) just behind the packing gland, one at the exit from the hull, and the one on the strut by the prop. By the way, the 2 inch shafts are not undersized for the boat...

Stick check the prop blades once you get it on the hill. Hold a stick against the rudder and slowly sweep the blades by it. All should have the same clearance within say 1/8". If more than that pop the prop and dial indicate shaft near the end of the taper. If bent, pull the whole shaft and coupling and have it straightened at a prop/shaft shop. Then have them skim cut the coupling face true to the shaft.

SoWhat said:

Sounds like you have all the bases covered. You should be able to use a dial indicator to check runout. In my opinion any bottom contact that would bend a shaft would trash your props.

Bearing wear is normal and shafts would have to be pulled to replace them. Any up or down movement is signal for replacement. Back and forth movement would lead you to transmission.

Engine alignment is another area to explore. You should be able to get it within .002-.003 if you're patient. Alignment assumes the mounts are in good condition and of proper hardness. Run engine at the vibration rpm, check each mount for excessive vibration.

Typically most drivetrain issues will vibrate at all speeds. Were your props scanned? If they were certified to Class III, pitch deviation of +/- 4% for each blade is allowed. You might want to have them tuned to a higher Class.

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There will definitely be engine alignment since we have to take the props out to replace the cutlass bearings.

The props were scanned, yes, and tuned to a class 1 according to the documentation. I am not that versed in this, so if that is not as good (internet searches are not helpful here) please let me know.

Lepke said:

In my time I worked in yards and owned a yard. Usually when a yacht damages a prop it bends the shaft a little, too. Most yacht builders put in the smallest shaft they can get away with. Sometimes the strut gets out of alignment, too. Especially in grounding where the boat weight gets put on the strut.
It's worth the time to check the strut and shaft rather than find you still have a vibration when you're back in the water.

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See Rufus note below - these are some big shafts, so I don't think OA cheaped out on that front. However, your advice is good - if the timing works I will have the shafts tested and trued.

Rufus said:

FYI, our 44 OA has three cutless bearings per shaft....one (composite shell) just behind the packing gland, one at the exit from the hull, and the one on the strut by the prop. By the way, the 2 inch shafts are not undersized for the boat...

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Oh good info! I didn't even think to ask, but I would have found out here in a few hours!

Ski in NC said:

Stick check the prop blades once you get it on the hill. Hold a stick against the rudder and slowly sweep the blades by it. All should have the same clearance within say 1/8". If more than that pop the prop and dial indicate shaft near the end of the taper. If bent, pull the whole shaft and coupling and have it straightened at a prop/shaft shop. Then have them skim cut the coupling face true to the shaft.

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Good advice!

I like Ski's simple approach. It is most likely that if the shaft is bent from a hit it is external to the hull.

What a lot of people miss when aligning couplings (on boats) is to compensate for shaft sag when uncoupled. The more the overhung length (or heavier the coupling half), the more sag there will be. That is why it is important to rotate the assembly and measure, as in Jay Leonards post.

When I had my boat surveyed prior to purchase, the surveyor showed me that he could wiggle the prop (clunk, clunk, clunk) and said that the cutless bearing needed to be replaced. When I hauled for that, the yard began by pulling the prop and noticed that it was just a tiny bit loose on the shaft. With the prop removed, there was no clunk. It was the prop that was wiggling, not the shaft in the cutless bearing. Yeah! Since I was already hauled, I spent my money on a prop tune-up and bottom paint.

My vibration wasn't bad before, but is now even better, either because of the prop tune-up, putting the prop on tight, or the psychological effect of having spent the money. Maybe somebody else can have the same luck.

Thanks for all of the suggestions. Here's an update after Day 1 of being in the yard. The boat was hauled yesterday, and I am headed back to the yard today (Day 2) for any updates.

We got the boat out and on the hard, no issues or problems in that process, which is always a bit unnerving.

The cutlass bearings at the struts are in excellent condition. No movement at all side to side, and they appear in good working order.

Both props and shafts spin easily, do not seem like they are rubbing or have any issues there, which can indicate a transmission issue, among other things. Neither shaft moves in/out either, which is good.

There is no visible damage anywhere. As a reminder, the props were taken off 6 weeks ago and the starboard one did show a defect. That is where most of the vibrations had come from. Both props were updated to a Class I spec - someone asked about what they were and having them improved. They are in as good condition as possible as far as I understand.

Shafts were dialed out and looked perfect.

At this point, we were thinking the biggest culprit was engine alignment, and were not going to pull the shafts - after all, the cutlasses looked excellent, shafts dialed out well, no issues.

I do have two engine mounts, one on each engine, both in the forward right corner, that the underlying metal mount has some rust on it. From my examinations of them while underway, I have never seen any movement, but while I have the boat out and am troubleshooting this problem, I will likely have the underlying metal replaced. The mounts themselves from the engines to the adjustable part are all in perfect condition.

While the yard was attempting to remove the packing material from the shaft glands (traditional ones, not dripless) the bolts and surrounding metal crumbled. I have no idea how old these were, but I assume original (31 years old). They had grounding connections, but I am going to be validating those today/this week.

As a result, the shafts now need to come out so we can put new shaft seals on. I am not going to send the shafts out, as it seems there is a huge wait to get that work done, which means I'm stuck in a hotel for weeks while the boat sits. If there is any observed damage on the shafts when they are out, of course that will change things.

For now, we (yard+me) think that this is mostly engine alignment since everything else looks in excellent shape.

Have the yard inspect motor mounts. If older than 20 years I'd recommend new ones.

sunchaser said:

Have the yard inspect motor mounts. If older than 20 years I'd recommend new ones.

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The motor mounts are original and are all steel, no rubber of any kind. They are in pristine condition with no issues. The underlying mounting block (noted above in my post) on two of the 8 need to be replaced, but that's it.

stevemitchell said:

The motor mounts are original and are all steel, no rubber of any kind. They are in pristine condition with no issues. The underlying mounting block (noted above in my post) on two of the 8 need to be replaced, but that's it.

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Wow, solid mounts? That seems unusual.


I had a slight vibration issue once and it turned out the prop wasn't seated on the shaft taper properly. Apparently this is not uncommon, and more common when props are installed under water. Trapped water can prevent properly seating. A dry fit is greatly preferred, which you can do now.

twistedtree said:

Wow, solid mounts? That seems unusual.


I had a slight vibration issue once and it turned out the prop wasn't seated on the shaft taper properly. Apparently this is not uncommon, and more common when props are installed under water. Trapped water can prevent properly seating. A dry fit is greatly preferred, which you can do now.

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Hmmmm now that I think about it, it could be that there is something under the mount and in between it and the metal structure below. This pic is from 2 years ago, and I couldn't find another one closer up. I'll take a look when I am back later today. If there is some vibration material under there, it's not easy to see.

I still think replacing them all is not necessarily needed unless it can be done relatively easily. I'll ask the yard.

Ah, good point on the prop seating. The vibrations were there before the props were removed, and got worse after a suspected underwater strike of a log or something like that. They got a lot better once the props were tuned. But it wouldn't take much to check this while it is out of the water anyhow.

There is rubber under that metal cup looking device. I also vote for replacing since they are over 30 years old.

Ski in NC said:

Stick check the prop blades once you get it on the hill. Hold a stick against the rudder and slowly sweep the blades by it. All should have the same clearance within say 1/8". If more than that pop the prop and dial indicate shaft near the end of the taper. If bent, pull the whole shaft and coupling and have it straightened at a prop/shaft shop. Then have them skim cut the coupling face true to the shaft.

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Not long after I bought this boat, I had my prop pulled to reduce the pitch because of overloading. I had also noticed a bit of vibration as I shoved the throttle forward getting on plane. The prop looked clean with no dents anywhere when it came off, but the prop shop owner told me that one blade was out of true with the other four by almost and inch and was likely the source of my vibration. I commented to him how good the prop looked coming off the boat and that i found it hard to believe it was that bad. His comment was that he sees a lot of brand new props like that. It is a Hy Torq prop.

So while sticking the prop is a darned fine idea, there CAN be another explanation for why the results look questionable. I like the idea of pulling the prop and getting a dial indicator on it as Ski mentions. Belt and suspenders.

Since the props were tuned to Class I just 6 months ago, and absent any strikes, I'm not seeing a lot of value in tuning them again. Though if there is time, I suppose a quick scan couldn't hurt.

twistedtree said:

Since the props were tuned to Class I just 6 months ago, and absent any strikes, I'm not seeing a lot of value in tuning them again. Though if there is time, I suppose a quick scan couldn't hurt.

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They are only class 1 when they reenter the water. One does not always feel the bumps which can make them otherwise. Trying to resolve vibration during a haul seems like the right time to remove all doubts about each and every item in the drive train and waste of time and money not to do so.

twistedtree said:

Since the props were tuned to Class I just 6 months ago, and absent any strikes, I'm not seeing a lot of value in tuning them again. Though if there is time, I suppose a quick scan couldn't hurt.

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Class 1 is probably as good as the average prop shop will get.
Wonder if the props were lapped to the shafts when installed?
You could chase alignment issues forever and then discover a transmission gear is worn and only shows up at certain rpm.

I'm happy as long as forward and reverse work.

rgano said:

They are only class 1 when they reenter the water. One does not always feel the bumps which can make them otherwise. Trying to resolve vibration during a haul seems like the right time to remove all doubts about each and every item in the drive train and waste of time and money not to do so.

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I think you are right. Penny wise and pound foolish.

The shop I took mine to scanned them for free, so why not scan them again. Mine each had one blade way off the others. Had them repitched down 1/2” and trued up. $800 for each prop.

The props were just tuned and are Class I. We're verifying that of course, but I doubt they have changed in the last 4-6 weeks.

We did inspect the motor mounts and they do have rubber under the bells. I don't know why I assumed they didn't. This is my 7th boat and I've changed these before. I will chalk it up to living on land the last 48 hours and very long days....

The motor mounts could potentially be original, but there is no way of knowing. I will definitely be replacing them later this year in the water. Doing it while I am out would be great, but we have enough other work already scheduled, and all of the local yards and people are super busy, so trying to do it now would add at least a week if not two on a 2 week stay already.

Shafts are out and look great, no damage, no other problems found.

Based on process of elimination so far, the vibration is either coming from being out of alignment or the engine mounts (or both of course). We'll be replacing the failed shaft seals, getting everything back together, and do a good engine alignment after the boat sits in the water a few days, which likely has not been done in a long time.

That should reduce the vibrations, and then later this year I'll replace the motor mounts and do another alignment.

twistedtree said:

Since the props were tuned to Class I just 6 months ago, and absent any strikes, I'm not seeing a lot of value in tuning them again. Though if there is time, I suppose a quick scan couldn't hurt.

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6 *weeks* ago, not months.

Comodave said:

The shop I took mine to scanned them for free, so why not scan them again. Mine each had one blade way off the others. Had them repitched down 1/2” and trued up. $800 for each prop.

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They are being re-scanned, but we don't expect any issues there. If for some reason they are out of whack after 6 weeks then what am I running over!

Are you sure the cutless bearings in the hull are not worn? Speaking from experience there is considerable sag/ bending/droop over the length of those long shafts. That can give you incorrect alignment readings at the face of the coupling flanges. And if the front and middle bearings are worn, there’s potential for shaft “whip” under some conditions. If the 42 is the same as the 44, now is the time to replace all of them. That said, the OA yard in Seattle told me they sometimes skip the one by the stuffing box, but then they compensate for the sag at that end when doing the alignment. Not clear who’s doing the work, but checking with the OA yard might be worth the call.

Everything has been pointed out to you that could be wrong. You can follow your time frame and splash the boat before every vibration point can be addressed. BUT everyone here is advising against it. In 25 years, I've seen plenty of people delay a bottom job to accommodate their schedule, no danger of further damage. Just delay the haul lout until you have time to do it right. No boating over trawler speed until it's fixed properly. I have a feeling you have a boating trip planned and won't admit that's why you're in a time crunch. You know we'll all tell you to delay the trip. I Hope I'm wrong.

This thread got me to thinking about how to gauge if and whether there is an improvement based on the work done. I recently downloaded an app for measuring sound and have been using it as I work on soundproofing the engine room. I took Db readings at low and high rpm with engine hatch off, hatch on, rug covering, first improvement, etc. Changes are slight but verifiable.

So what if there was an app for vibration? Turns out that there is (are). I have no experience with them yet (and some reviewers claim that they contain spyware, just like your breakfast cereal box).

Place the phone in a standard location and get high/low rpm reading. Port engine, stbd engine, both (working on synchronization). Now, one would at least have a baseline when the future question of "did the vibration just increase?" issue arises.

One of the things I found with my sound meter app is that the Db reading at 1,500 rpm is basically the same as at a spot near 1,800 rpm. DB was rising (not entirely uniform) and then took a little dip. This might explain the mysterious "sweet spot" we tend to find on a certain motor.

Measuring vibration might also identify a plateau that we identify as a sweet spot in addition to having a vibration baseline.