[Public-List] Stern Tube Repair

Hernán Scarnichia via Public-List public-list at lists.alberg30.org
Wed Aug 23 20:28:10 PDT 2017

The stern tube has de-bonded from the hull, probably from the shaft banging
against the stern tube. This has been ongoing since last fall when I asked
on this list (and got some very helpful replies).

On my boat (#414) there is none of the sealant that others found between
shaft log tube and hull, so possibly a previous owner removed this....

I have re-aligned the engine a couple times and it seemed to improve for a
while but the problem seems to be getting worse now. I aligned it the best
I could and when looking at the shaft with the engine running and in gear
there is still some vibration on the after part of the shaft (hose and
shaft loge move around). This movement is worse when moving at speed and
barely noticeable when running the same RPM tied to the dock.
Maybe the 2 blade prop is causing vibration because of the water rushing
past the keel?
Maybe the cutless bearing is worn?

Soooo i'm getting ready to finally fix this.

I have not hauled out yet so I don't have the exact measurements of some
parts and was hoping someone that has done this before can help confirm the
measurements so I can order parts and have everything ready for haul out or
offer any other tips for this job.

Plan A is to remove the engine and fuel tank under cockpit to get better
access and remove the stern tube, clean everything up and glue the tube
back on (assuming it is in good shape). I'm planning on using Pettit
FlexPoxy to glue it. I will also replace cutless bearing, check shaft and
coupler for straightness and change to a 3 blade prop. (campbell sailor
12x8 already ordered)

searching through past list messages I find that the cutless bearing is
is it safe to assume that this is the same for all our boats?

what size packing for the prop shaft stuffing box?

Also on previous list messages I see that the shaft log tube and the
stuffing box are not the same diameter? (1-3/8 tube and 1-1/2 stuffing box)
what size of hose have you used?

Does anyone remember what the clearance is between the shaft log tube and
the shaft?
The shaft is 7/8 and I measured the outside of the shaft log tube to be
1-5/16 so I'm guessing the inside might be 1 inch?
This would leave 1/16 clearance which does not seem enough to prevent the
shaft from touching the tube when engine vibrates/moves....

this makes me think of Plan B: build a new fiberglass stern tube that is
bigger and allows the shaft to move more.

anybody else has a problem of the shaft touching the stern tube? were you
able to correct this with just engine alignment?
I have a universal m3-20b diesel, maybe this vibrates more than the old
Atomic 4?

Thanks for sharing your knowledge


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