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Old 08-10-2020, 12:41 AM   #1
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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!
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Old 08-10-2020, 12:57 AM   #2
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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.
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Old 08-10-2020, 01:01 AM   #3
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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 theyíre really bad you can move it by hand.
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Old 08-10-2020, 01:10 AM   #4
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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 6Ē 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 donít 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 itís normal shape before doing the alignment. Good luck.
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Old 08-10-2020, 01:25 AM   #5
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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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Old 08-10-2020, 01:38 AM   #6
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Originally Posted by Comodave View Post
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 6Ē 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 donít 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 itís normal shape before doing the alignment. Good luck.


Gotcha - so doing an engine alignment in the water prior to haul out could be a way of telling whatís wrong or at least gathering some more data. Good point.
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Old 08-10-2020, 04:02 AM   #7
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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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Old 08-10-2020, 07:40 AM   #8
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Old 08-10-2020, 08:55 AM   #9
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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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Old 08-10-2020, 09:07 AM   #10
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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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Old 08-10-2020, 10:35 AM   #11
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Quote:
Originally Posted by SoWhat View Post
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.
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.

Quote:
Originally Posted by Lepke View Post
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 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.

Quote:
Originally Posted by Rufus View Post
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...
Oh good info! I didn't even think to ask, but I would have found out here in a few hours!

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Originally Posted by Ski in NC View Post
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.
Good advice!
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Old 08-10-2020, 10:38 AM   #12
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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.
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Old 08-10-2020, 10:40 AM   #13
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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.
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Old 08-11-2020, 12:41 PM   #14
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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.
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Old 08-11-2020, 01:08 PM   #15
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Have the yard inspect motor mounts. If older than 20 years I'd recommend new ones.
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Old 08-11-2020, 01:10 PM   #16
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Have the yard inspect motor mounts. If older than 20 years I'd recommend new ones.
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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Old 08-11-2020, 02:36 PM   #17
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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.

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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Old 08-11-2020, 02:43 PM   #18
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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.
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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.
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Old 08-11-2020, 04:31 PM   #19
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There is rubber under that metal cup looking device. I also vote for replacing since they are over 30 years old.
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Old 08-11-2020, 04:56 PM   #20
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Quote:
Originally Posted by Ski in NC View Post
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.
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.
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