Shaft vibrating.
- Thread starter rocky6450
- Start date
The friendliest place on the web for anyone who enjoys boating.
If you have answers, please help by responding to the unanswered posts.
If you have answers, please help by responding to the unanswered posts.
Make sure the key is not binding up in keyway, preventing prop from fully seating on taper.....ditto if key extends beyond end of prop, such that it rides up curved machining at end of keyway for a false prop seat
this is a great point. a scribed line on shaft where the prop rides now vs. another with the key out might show that.
easier to do with the boat out of the water obviously.
marking the nut position against the prop, key in vs. key out will do the same thing. if the nut can tighten more turns with the key removed, the key could be the issue.
Slowmo
Senior Member
- Joined
- Oct 19, 2018
- Messages
- 453
- Location
- United States
- Vessel Name
- Esprit
- Vessel Make
- 40' Tollycraft tricabin diesel
Did you have the prop actually balanced? That's more than just making sure it is straight. I did that on our old boat and it made a big difference despite the fact the prop only rotated about 600RPM. Fairly cheap thing to do.
Comodave
Moderator Emeritus
- Joined
- Jul 2, 2015
- Messages
- 21,273
- Location
- Au Gres, MI
- Vessel Name
- Black Dog
- Vessel Make
- Formula 41PC
On our last boat we took the props and had them scanned. They did not have any visible damage but on each prop one blade was quite a bit out of pitch. Had them rebuilt and some of the vibration went away. $800 per prop, 4 blade 24” diameter props.
Choices
Guru
- Joined
- Apr 16, 2018
- Messages
- 898
- Location
- Montgomery, Tx
- Vessel Name
- Choices
- Vessel Make
- 36 Grand Banks Europa
You can get a square flange to flange and still have a droop in the shaft. If less than 30" to stuffing box usually not a problem.
With the boat tied in the slip, in gear, lay a wrench on the prop shaft and feel for vibration. Be carefull of rotating things.
If you have no vibration there, it is down stream in the prop area.
Motor mounts will settle with time, you should realign the shaft after several weeks.
Depending on the prop saver, if used, you can align some to the hubs. Otherwise slide the shafts up if possible, usually is.
If all else take prop to new place to be checked. Shafts can seldom be straightened.
A vibration will trash the tranny end seals and bearings. The wrench test is an easy test.
With the boat tied in the slip, in gear, lay a wrench on the prop shaft and feel for vibration. Be carefull of rotating things.
If you have no vibration there, it is down stream in the prop area.
Motor mounts will settle with time, you should realign the shaft after several weeks.
Depending on the prop saver, if used, you can align some to the hubs. Otherwise slide the shafts up if possible, usually is.
If all else take prop to new place to be checked. Shafts can seldom be straightened.
A vibration will trash the tranny end seals and bearings. The wrench test is an easy test.
SteveK
Guru
- Joined
- Jul 5, 2019
- Messages
- 5,071
- Location
- Gulf Isalnds BC canada
- Vessel Name
- Sea Sanctuary
- Vessel Make
- Bayliner 4588
The following suggests alignment first, then install drivesaver.
https://propshopinc.com/globe-drivesaver-installation-instructions/
Choices
Guru
- Joined
- Apr 16, 2018
- Messages
- 898
- Location
- Montgomery, Tx
- Vessel Name
- Choices
- Vessel Make
- 36 Grand Banks Europa
Good. That tells you problem is downstream.
I would pull prop and have it rebalanced. I had one redone that had hit something, after trying it had a slight vibration. The second time they nailed it.
Also on a trip I picked up a 6'x6' tarp, and immediately felt something wrong. Diver cut it off.
You may have a slightly off prop. Although a pain, only option is to let them balance it again with you watching. Not that it will help, but you will learn something.
An oversized prop can also cause a hydraulic thump on the bottom. Pretty rare, and goes away at certain rpm and seas.
With engine running go down and just listen and feel. Maybe something is moving, a broken bracket, lose bracket, etc. Tighten everything.
I think you will find it by process of elimination.
What Soo Valley is stating is true for soft prop savers. They can compress and give. A quick tell on those is they will get hot after thirty minutes at speed from compression. The newer harder machined donuts not so much.
But if you can remove it and check it is best.
I would pull prop and have it rebalanced. I had one redone that had hit something, after trying it had a slight vibration. The second time they nailed it.
Also on a trip I picked up a 6'x6' tarp, and immediately felt something wrong. Diver cut it off.
You may have a slightly off prop. Although a pain, only option is to let them balance it again with you watching. Not that it will help, but you will learn something.
An oversized prop can also cause a hydraulic thump on the bottom. Pretty rare, and goes away at certain rpm and seas.
With engine running go down and just listen and feel. Maybe something is moving, a broken bracket, lose bracket, etc. Tighten everything.
I think you will find it by process of elimination.
What Soo Valley is stating is true for soft prop savers. They can compress and give. A quick tell on those is they will get hot after thirty minutes at speed from compression. The newer harder machined donuts not so much.
But if you can remove it and check it is best.
Choices
Guru
- Joined
- Apr 16, 2018
- Messages
- 898
- Location
- Montgomery, Tx
- Vessel Name
- Choices
- Vessel Make
- 36 Grand Banks Europa
Also, are both engines the same? Why are you running both at different rpms?
Comodave
Moderator Emeritus
- Joined
- Jul 2, 2015
- Messages
- 21,273
- Location
- Au Gres, MI
- Vessel Name
- Black Dog
- Vessel Make
- Formula 41PC
I would have the prop checked as mentioned above. It also could be the prop isn’t seated properly on the shaft. The key could be out of position or it could be a cutless bearing. They make feeler gauges that are plastic so you can curve the feeler gauge around the shaft and put it in between the shaft and cutless bearing to check wear. There are guides as to how much measurement is good depending on shaft diameter.
You can do a lot of tail chasing trying to hunt down a vibration; it's not intuitive and even skilled pros can get this wrong with the best of intentions. Once you exhaust the usual suspects, you can waste a lot of time and money, there are folks who will come in and sensor the engine and identify the exact source. In the long run that may be cheaper than a lot of trial and error.
Here's an example, when a vibration is present, a lot of folks will fixate on alignment. In fact, because misalignment is constant, i.e. it induces a constant bow in the shaft, even if it can't be seen, it rarely is the source of vibration. While it's important to correctly align the engine and shaft (those are two separate types of alignment), doing so will rarely eliminate the vibration issue.
Use a dial indicator to make certain the shaft is centered in the coupling/coupling is centered on output flange. You can also use a dial indicator to make sure the shaft isn't bent.
An incorrectly installed prop, one that is binding on the key, is a common source of vibration.
Prop condition and blade alignment can really only be checked by a prop shop, preferably one using MRI or PropScan.
Motor mounts are frequently the source of vibration, if they are loaded unevenly, especially of the engine is teetering on two mounts diagonally, i.e. port front and stbd rear. You can still have proper shaft flange alignment with this scenario.
More here...
Engine alignment https://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/
Shaft alignment https://stevedmarineconsulting.com/the-ins-and-outs-of-shaft-alignment-part-ii/
Engine alignment step by step https://stevedmarineconsulting.com/wp-content/uploads/2021/04/TaskSheet190-EngineAlignment-05.pdf
Couplings https://stevedmarineconsulting.com/wp-content/uploads/2019/06/ShaftCouplings179FINAL-PBB.pdf
Prop installation https://stevedmarineconsulting.com/propeller-installation/
Here's an example, when a vibration is present, a lot of folks will fixate on alignment. In fact, because misalignment is constant, i.e. it induces a constant bow in the shaft, even if it can't be seen, it rarely is the source of vibration. While it's important to correctly align the engine and shaft (those are two separate types of alignment), doing so will rarely eliminate the vibration issue.
Use a dial indicator to make certain the shaft is centered in the coupling/coupling is centered on output flange. You can also use a dial indicator to make sure the shaft isn't bent.
An incorrectly installed prop, one that is binding on the key, is a common source of vibration.
Prop condition and blade alignment can really only be checked by a prop shop, preferably one using MRI or PropScan.
Motor mounts are frequently the source of vibration, if they are loaded unevenly, especially of the engine is teetering on two mounts diagonally, i.e. port front and stbd rear. You can still have proper shaft flange alignment with this scenario.
More here...
Engine alignment https://stevedmarineconsulting.com/the-ins-and-outs-of-engine-and-shaft-alignment/
Shaft alignment https://stevedmarineconsulting.com/the-ins-and-outs-of-shaft-alignment-part-ii/
Engine alignment step by step https://stevedmarineconsulting.com/wp-content/uploads/2021/04/TaskSheet190-EngineAlignment-05.pdf
Couplings https://stevedmarineconsulting.com/wp-content/uploads/2019/06/ShaftCouplings179FINAL-PBB.pdf
Prop installation https://stevedmarineconsulting.com/propeller-installation/
catalinajack
Guru
Yup, the only the way ensure an alignment within acceptable limits.
