Shaft Alignment Question

[OrangeCrush]

Hello all,



Apologies for jumping on this thread but there appears to be some good knowledge here. I had a new shaft log, shaft, packing gland and cutlass bearing installed last year, the propeller balanced, and the motor aligned with the mechanic reporting .003" at the coupling. I have no vibration whatsoever under motor power at any rpm, but when sailing above 5 knots (with prop in neutral as per yanmar manual) I feel a vibration, almost a flutter, throughout the entire drivetrain.



Could this be an alignment problem if there is no such vibration under motor power? What could cause the propeller to wobble when being pulled rather than driven through the water? I'm planning to check the alignment again myself, but I have a feeling I will be unable to improve upon it. If so, should I live with the vibration at the risk of wearing out the cutlass bearing, invest in a feathering prop, or something else? Any advice is greatly appreciated.

[Sailmonkey]

The flutter is more than likely from the different water columns the propellor is passing through.

I’ll assume you’ve got a three blade prop, as it’s turning through the deadwood two blades are in the flow on either side of the hull, while one is astern of the deadwood.

This alternates high/low and sets up a weird little flutter.

We had it too, a feathering prop is the cure.

[OrangeCrush]

Originally Posted by Sailmonkey

I’ll assume you’ve got a three blade prop, as it’s turning through the deadwood two blades are in the flow on either side of the hull, while one is astern of the deadwood.

I do have a 3-blade fixed prop and a full keel so this makes a lot of sense. I asked about this on another thread but I didn't fully understand the concept until now, so I appreciate for the clear explanation.

I guess my question now is whether it's actually doing any damage or not since a new prop is not really in my budget this year. Since it's happening in neutral only, I'm guessing it's not straining the transmission itself. I would hate to mess up my new cutlass bearing, though... I guess I'll see if any lateral play has developed in the shaft through the course of the season and decide from there.

[Sailmonkey]

There’s no real load on anything when this is happening, so I don’t see how you could possibly damage your cutlass. If anything the cutlass is wearing more from the prop spinning than the vibrations

[OrangeCrush]

Originally Posted by Sailmonkey

There’s no real load on anything when this is happening, so I don’t see how you could possibly damage your cutlass. If anything the cutlass is wearing more from the prop spinning than the vibrations

Fair point... I guess I was assuming that if a bad alignment could hasten the cutlass bearing’s demise then a wobble would have more or less the same effect. Yes the spinning shaft is what wears it, but when it’s off center it wears the rubber of the cutlass unevenly, or adds some torque to the friction.

Even so, it’s really a subtle thing and I agree with you that it’s probably not doing damage. Just paranoid about this sort of thing I guess...

[EllisElectric]

No one mentioned the alignment is to the fixed shaft, so the motor shaft needs to move in order to align. That means adding shims under foot of motor and moving front or back feet side to side. How is that accomplished, any videos etc?

[Sailmonkey]

Originally Posted by EllisElectric

No one mentioned the alignment is to the fixed shaft, so the motor shaft needs to move in order to align. That means adding shims under foot of motor and moving front or back feet side to side. How is that accomplished, any videos etc?

Tons of videos on YouTube. The mounts are adjustable as well, no shimming is going on in most recreational vessel installations.