Stern Tube or P Bracket Misaligned

[goeasy123]

What's the easiest way to fix this problem? Any innovative opinions gratefully received. See attached pics.

A Najad 400. It isn't an engine alignment problem.

When the drive chain is perfectly aligned the prop shaft goes through the stern tube at an angle. The diagram (Stern Tube 2_1) is what I think is going on. Pic (Stern gland off centre) shows the prop shaft bearing harder on the top of the Volvo stern gland than on the bottom. The gland wears prematurely and leaks.

Pic (P Bracket and stern tube) shows the prop shaft coming out of the stern tube closer to the bottom than the top. I could shorten the P bracket, but that might be a big job and I'm not sure the engine will drop down enough on the new engine mounts.

Pic (stern gland back) is where the Volvo stern gland is clamped to the stern tube. Maybe I can remake this part, but how?

Someone has suggested a PSS seal. That could work, but there might be too much out-of-alignment for that. And PSS don't do a seal carrier to fit the 54mm diameter stern tube OD designed for the Volvo seal.

[SailingHarmonie]

Why not just a standard packing gland? the rubber hose will absorb some misalignment without issue.

If the shaft sits straight in the P-bracket cutless bearing when properly aligned to the engine AND does not touch the stern tube, this really doesn't seem like a hard fix... Ditch the Volvo gland.

[Ballsnall]

Originally Posted by goeasy123

What's the easiest way to fix this problem? Any innovative opinions gratefully received.

There is only one good solution I can see and that is to machine the outer diameter of your stern tube to be concentric with your prop shaft. I would fabricate a cutter that ran around the prop shaft even a hand driven one would do the job or run it off a battery drill.

If you stern tube is thick enough just machine it smaller otherwise build up the stern tube first then machine down to original diameter.

You could machine an eccentric bush and epoxy it over your stern tube to make it concentric and use a larger gland hose, this would eliminate the need to machine the stern tube.

[goeasy123]

Originally Posted by Ballsnall

There is only one good solution I can see and that is to machine the outer diameter of your stern tube to be concentric with your prop shaft. I would fabricate a cutter that ran around the prop shaft even a hand driven one would do the job or run it off a battery drill.

If you stern tube is thick enough just machine it smaller otherwise build up the stern tube first then machine down to original diameter.

You could machine an eccentric bush and epoxy it over your stern tube to make it concentric and use a larger gland hose, this would eliminate the need to machine the stern tube.

That might work. I'll have to look at the wall thickness of the tube when I get it out of the water. There's enough shaft showing that I might be able to add an extra bit on.


However, this is a hole under the water line and theoretically the new to old glass joint should be a 12 to 1 scarf. That might be an issue.

[Ballsnall]

Originally Posted by goeasy123

That might work. I'll have to look at the wall thickness of the tube when I get it out of the water. There's enough shaft showing that I might be able to add an extra bit on.


However, this is a hole under the water line and theoretically the new to old glass joint should be a 12 to 1 scarf. That might be an issue.

I meant epoxy an eccentric bush over the top of stern tube to make it concentric.
Definitely do not try to extend the stern tube, that would definitely be an exciting issue.

[Bowdrie]

A good fiberglass person would have no trouble cutting out the original stern tube and glassing in a new one made of filament wound tubing that was perfectly aligned.
https://centekmarine.com/product/category/tubing/

[goeasy123]

Thanks. Both sound like good solutions. I'll ponder.