Vibrating shaft at slightly high revs.

[Cheechako]

Originally Posted by Hoohaa

Chee
Its a visual vibration.

Forgive me if I have missed part of the thread on this,
So is it an actual problem when you motor or you just dont like how it looks?
Thinking back, it seems to me many of my boats/shafts looked a little wobbly under power... I always concluded it was unbalanced prop pressures and a flexible system. ie: when one blade rotates near the hull, it probably see different forces than the other two blades, the shaft packing is in a rubber tube, the engine on rubber mounts, so the whole thing flexes a bit.
The most vibration I ever had, had no observed wobble, the shaft was very short packing to the engine on that one.

[Hoohaa]

Cheech
There is a vid at the start of this thread. Its a significant wobble from side to side at the stern flange. I believe it destroyed my strut, which was rebuilt a couple of years ago when they also replaced my shaft ( needlessly).

[Hoohaa]

So. I am going to pull the trigger on the Sigmadrive but I have also had an interesting conversation with the distributor here in Australia.
I have sent him most of the info on my prop shaft including the sketch showing rough dimension below.
He is of the opinion that the shaft is basically unsupported from the skeg? through to the gearbox and that it should have a cuttles bearing at the rear of the stern tube to supply additional support.
There is infact a bearing installed at the rear of the stern tube but it is clearly oversise. Allowing to shaft to rest down into the bottom of the stern tube which you can see in the second picture. (zoom in)
So its a Sigma drive for me and then a correctly sized cuttles bearing for the rear of the stern tube when she is next out of the water. Stay tuned.
Any opinions on the additional bearing at the rear of the stern tube?
I know I have broached this idea earlier in this thread.

[GILow]

And to think a replacement coupling is such a cheap experiment. Sigh.

[Hoohaa]

GILow. I have looked long and hsrd at that coupling. Measured, checked every I could measur.
I phoned the manufacturer's and spoke to the guy who knows about this stuff, with a view of getting a new one. He suggested aligning the motor and then bolt it together without the coupling. If its the coupling, then it should run smooth. Makes perfect sense.
It was worse than ever. Believe me if I thought it was going to make a difference then it would be replaced.
Turns out the wear around the edge is to stop it fouling with a wooden panel. I don't no why they didn't trim the panel instead of the coupling. Maybe the panel machined the coupling.
Anyways. Its more than $300 bucks for a new one so for now I am going to blow another grand on a Sigmadrive. Which seems to have the best chance for improvement and I Will do away with the coupling as it won't be needed anymore.
Are there any thoughts on the bearing in the rear of the stern tube?

[Hoohaa]

Sorry about the bad grammar. Fat fingers on a Samsung.

[Three Sisters]

Originally Posted by Hoohaa

Are there any thoughts on the bearing in the rear of the stern tube?

Yes.

The propeller shaft is against the bottom of the stern tube at the exterior. I would want to know if it is also at the bottom of the stern tube at the entry to the machinery room. But then again you say it is not tight-fitting around the propeller shaft. Being in the water, some of these checks are difficult or impossible. And the engine alignment could not be accomplished using, two, was it ?, professionals just recently.

And with the motor mounts moving as they are tightened, this just leaves me at a loss for words.

[Cheechako]

I would want a bearing in that stern tube for sure. That's a long unsupported shaft. It seems to me that is likely part of the problem. But also, the shaft should not move much in the cutlass bearing, maybe 1/32" at the most.
If it were mine I would put in two new cutlass bearings, disconnect the engine coupling and note where the shaft naturally rests relative to the engine. Then adjust the engine to match where the shaft is.

[Cheechako]

Originally Posted by Cheechako

Forgive me if I have missed part of the thread on this,
So is it an actual problem when you motor or you just dont like how it looks?
Thinking back, it seems to me many of my boats/shafts looked a little wobbly under power... I always concluded it was unbalanced prop pressures and a flexible system. ie: when one blade rotates near the hull, it probably see different forces than the other two blades, the shaft packing is in a rubber tube, the engine on rubber mounts, so the whole thing flexes a bit.
The most vibration I ever had, had no observed wobble, the shaft was very short packing to the engine on that one.

PS: I went back and saw the video again, that looks like every boat I've had.

[Hoohaa]

Originally Posted by Three Sisters

Attachment 164486

Yes.

The propeller shaft is against the bottom of the stern tube at the exterior. I would want to know if it is also at the bottom of the stern tube at the entry to the machinery room. But then again you say it is not tight-fitting around the propeller shaft. Being in the water, some of these checks are difficult or impossible. And the engine alignment could not be accomplished using, two, was it ?, professionals just recently.

And with the motor mounts moving as they are tightened, this just leaves me at a loss for words.

This shot was taken before the mechanic aligned it the second time. He actually raised the engine about 20mm to try and get it clear of the stern tube. Later when i unbolted the coupling, the shaft sprung back down with a bit of force.
The shaft currently can moves up and down about 10 plus mm when disconnected. This would indicate that it has some clearance along the length of the stern tube. I try to place the shaft on the middle of this movement when realigning it but that side of it is a little hit and miss.
Regarding the mount movement when tightening. Its very minor. I notice it when rechecking the alignment gaps and think it's because one of themounts is not fully loaded. Resulting in it pulling down a corner of the engine a smij.
This mount does seem to vibrate a little more than the others at particular revs. That's why I suspect that it's not carrying the same loads as the others.

[Three Sisters]

Originally Posted by Hoohaa

This shot was taken before the mechanic aligned it the second time. He actually raised the engine about 20mm to try and get it clear of the stern tube. Later when i unbolted the coupling, the shaft sprung back down with a bit of force.
The shaft currently can moves up and down about 10 plus mm when disconnected. This would indicate that it has some clearance along the length of the stern tube. I try to place the shaft on the middle of this movement when realigning it but that side of it is a little hit and miss.
Regarding the mount movement when tightening. Its very minor. I notice it when rechecking the alignment gaps and think it's because one of themounts is not fully loaded. Resulting in it pulling down a corner of the engine a smij.
This mount does seem to vibrate a little more than the others at particular revs. That's why I suspect that it's not carrying the same loads as the others.

This has been a lengthy endeavor, however you have the advantage of being able to start from scratch at any point.

The strut at the propeller is not going to move. Is it even feasible to employ a laser in the machinery space with gauges ?

Then the shaft coupling.

The motor housing plate must meet with the shaft coupling dimensions as the strut is not adjustable.

If you are out of the water, you might consider removing the packing gland hose at the stern tube.

Best Regards

[Hoohaa]

Unfortunately I am on the water.
It won't be slipped for another 12 months. But when next it us. I will measure and lazer the crap out of it. I am a land surveyor by profession so I do have access to gear that will hopefully shed some light on the alignment of the stern tube and skeg or strut.
It will be very interesting to sight an instrument straight up its clacker and see once and for all if its aligned or not..

[Mainebristol]

I just saw this thread for the first time. I have trouble with a wobbly shaft, so I opened the Youtube with great anticipation.

You've got to be kidding. That sucker hardly moves. I WISH mine ran so true. On to the next thread...

[Hoohaa]

Originally Posted by Mainebristol

I just saw this thread for the first time. I have trouble with a wobbly shaft, so I opened the Youtube with great anticipation.

You've got to be kidding. That sucker hardly moves. I WISH mine ran so true. On to the next thread...

Might be good enough for your boat but it aint for mine.

[Three Sisters]

Originally Posted by Hoohaa

Unfortunately I am on the water.
It won't be slipped for another 12 months. But when next it us. I will measure and lazer the crap out of it. I am a land surveyor by profession so I do have access to gear that will hopefully shed some light on the alignment of the stern tube and skeg or strut.
It will be very interesting to sight an instrument straight up its clacker and see once and for all if its aligned or not..

This may or may not play out as important...but. Say for hits and giggles, the propeller shaft is not centered into the stern tube. Ok. So into the machinery space, there is the shaft packing gland with hose attached to stern tube. But wait. The propeller shaft is not centered. The hose to the stern tube must bend to meet the stern tube. The question being does this wrestling of the hose to meet the stern tube introduce enough stress onto the 1" propeller shaft to contribute to the wobble ? If it is a hose with flexible properties then it's propably a non-issue. If the hose at the packing gland is similar to reinforced exhaust hose, a short length, such as on a packing gland, will require mucho muscles to slide onto the stern tube and may contribute to this wobbling. Something that cannot be tested in the water, as far as I know.

If you are running the propeller on the stands for any length of time you may want an extra hand to water the cutlass bearing and stern tube bushing.

Do let us know what you find the problem to be.