Shaft vibrating.

[sunchaser]

Is the vibration above 2,000 RPM apparent when vessel in neutral at the dock?

 

[Crux]

WOW Great info Thanks Guys. Shaft alighn done recently. 2000 all around. Was better after that but still vibrates at 2000 rmp. Tamd 40 b diesel. Star engine the prob. cutless bearings new.after damage. After trip home I put on a spare prop and had original recondtioned. Dove and put it back on. Seems tight. no wiggle. Will double check it. I dont know if it was lap/seated when they put it back on at marina on land. I see they put a new key in. Damper plate is newly replaced also. Shaft brand new. Coupler looks great centered and tight I will double check anyway Thanks. Struts are good.according to marina when they did job.Nice new coupler but I will double check for dings and scratches. Re alighnment was done after new motor mounts. same day. About a month ago. I cruise at 1900 on that engine and 2200 on port with no problem.

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

 

[rocky6450]

Will check all. Thanks guys

 

[rocky6450]

Hi Sunchaser. Thank you ! Engine nice and smooth when not in gear. Darn Haaa

 

[Bmarler]

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.

 

[rocky6450]

Thank you ! Will re check

 

[Slowmo]

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]

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.

 

[rocky6450]

Hi slo mo. Thank you yes all scanned and re balanced

 

[Choices]

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.

 

[rocky6450]

Thank you choices. The shaft is new. I will check it anyway. WIll do tomorrow.

 

[rocky6450]

Hi Choices. Laid wrench on shaft while in gear. Nice. no vibration. New shaft and couplings look great. spaced 2000 of an inch all around

 

[SteveK]

No one has asked whether the coupling includes a DriveSaver. Getting an accurate alignment with a DriveSaver in place is near impossible save blind luck.

The following suggests alignment first, then install drivesaver.
https://propshopinc.com/globe-drivesaver-installation-instructions/

 

[Choices]

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.

 

[Choices]

Also, are both engines the same? Why are you running both at different rpms?

 

[rocky6450]

thank guys ! The Starboard engine doesn't vibrate at 1900 rpms.

 

[Comodave]

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.

 

[rocky6450]

HI Comodave. Thank you. I will check. Also, I will bring my spare prop into machine shop that did shaft and replace.

 

[Steve DAntonio]

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/

 

[catalinajack]

The following suggests alignment first, then install drivesaver.

https://propshopinc.com/globe-drivesaver-installation-instructions/

Yup, the only the way ensure an alignment within acceptable limits.

 

[rocky6450]

Thank you ALL !!!! I will check and advise. WIll go swimming in about 2 weeks to check prop.