Long Prop Shaft Alignment

[meridian]

How do you set up a shaft for alignment to the transmission when it is long and only has a cutless bearing in a strut just before the prop for support? I have one of the few Krogen 42's with twin Lehman 90's. There is sag in the shaft due to the weight of the shaft and the coupling when it is disconnected from the transmission.

 

[O C Diver]

Where is the stuffing box in relationship to the cutlass bearing and the transmission coupling?

Ted

 

[meridian]

Prop, strut, 4' shaft, PSS, 2' shaft, coupling

 

[Capt.Bill11]

The old school way is to find the weight of the shaft and then suspend the shaft using a hanging scale at the transmission end by half that weight.

 

[O C Diver]

If you're out of the water, loosen the PSS and move it forward. Center the shaft in the tube with a shim block. If you lube the block and the cutlass bearing with liquid soap (Joy), you should be able to turn the shaft if it's true between the bearing and the tube. The shaft resists turning if it's out of alignment with the cutlass bearing. Once the shaft is aligned with those two, see where the prop shaft coupling is in relationship to the transmission flange. This should eliminate the shaft droop for alignment purposes. When the alignment is done and everything except the stuffing box is bolted up tight, with the shim block removed, see if you can still turn the shaft by hand.

My trawler has a 13' x 2.5" shaft supported by the cutlass bearing and the transmission. When I was done with the alignment, with a new 10" cutlass bearing, I could still turn the shaft with one hand.

Ted

 

[Nomad Willy]

That's a very short shaft IMO.
I had an Albin25 w a shaft longer than that and it was only 1" dia. That one whipped around quite a bit .. or more.
With a 7' shaft and probably a 1.25" dia shaft I see no problem. Unlike standard shaft seals the PSS seal is more flexible but alignment is alignment. So the bore of the strut and the center of the seal should determine the shaft position fwd.

A. You can use a laser or illuminate the coupling and sight up the shaft line through the strut cutlass, through the PSS and the center of the shaft in the coupling should be visually centered.

B. Or if you're in the water just find the center of the possible shaft movement up-down and right-left. Think it through but that should dictate the location of the shaft.

If your shaft is real skinny the droop should be compinsated for in "B" with the shaft end of the coupling in your hand (or suspended from above w a string).
I really don't think you need to worry about the droop.

 

[Irish Rambler]

Mine was similar on our Broom 42.
I centred the shaft the same way as OC Diver's method and fitted a carrier bearing that eliminated the shaft whip.
I took meticulous care lining up the flexible coupling to the g/box so that everything ran true.
Cut down on noise/vibration as a result.