Vibrating shaft question

My problem sounded similar. I described it differently and I saw it as an occillation of the shaft between the gear and the stuffing box. I couldn’t detect vibration in the boat. It ended up as internal transmission problem that eventually cracked the case of the gear and led to the replacement of both transmissions. I had all of the alignment checked, props reworked, etc and that is what ended up happening. Definetly pursue alignment and props but I would take an oil sample of both gears and see what they say. Also look at your stringers to make sure that they are not rotting leading to the gear settling. My gears were ZF 350s which are no longer available and a mechanic I respect didn’t think much of them.

If it s a vibration, pull the wheel and have it checked by a good prop shop. Next would be to check the alignment.

Stringers shouldn't rot unless some cheap builders used wood in there.

There is a D bent in the shaft. Before it kills the clutch rear bearing, get it looked at.
Great shop at American Yacht, up the canal, just before Stewart. They can come to your year if needed.

Get th prop to a good shop, have the alignment checked as well as the shaft with a dial gauge to make sure it s true

Ralph what do you mean by a “D” bend in the shaft? Thanks

I don't mean to dismiss checking the prop and alignment of the coupler.
My comment was based on ; has a seeable vibration where the shaft meets up with the tranny.
IMO Alignment may cause some vibration more felt than visually observed.
When you can visually see the coupler shaking, something is bent and will damage the clutch.

I keep forgetting my swamp raised terminology is not understood by all.

Patience as I try to explain; Look at the letter D. As a diagram and not a letter I) , I ) .
The left side I is stright, the right side is bent ) . Both the same length.

Now imagine a long shaft, Straight is preferred it's whole length I. But if there is a bent in it, the whole length forms the ).
D bend.

I hope this helps.

Thanks I understand now.