[Public-List] Stern Tube Repair

George Dinwiddie via Public-List public-list at lists.alberg30.org
Thu Aug 24 13:48:37 PDT 2017


I rebedded the stern tube on Calypso this Spring. 

> On Aug 23, 2017, at 23:28, Hernán Scarnichia via Public-List <public-list at lists.alberg30.org> wrote:
> 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...

That's what bonds the stern tube to the hull. 

> 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?

Maybe the prop is out of balance or the shaft is bent. Or a multiple of these things. 

> 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.

I used 3M 5200. About 2 tubes of it. 

The waterproof seal is made by the cutless bearing housing against the hull. 5200 that, too. 

> searching through past list messages I find that the cutless bearing is
> 1-3/8.
> is it safe to assume that this is the same for all our boats?


> what size packing for the prop shaft stuffing box?

Some boats have a different size stuffing box. Mine was 1-1/4", but I've heard some are 1-1/2". Whether that's original or rework, I don't know. 

> 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?

Mine was 1-1/4" for both, and 1-1/4" stuffing box hose worked great. 

> 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....

I probably had 3/16" or 1/4" around the shaft. It's held in the center by the stuffing box (assuming you got genuine stuffing box hose) on one end and the cutless bearing on the other. 

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

Are you going to cast a new cutless bearing housing? It screws onto the threads of the stern tube. 

> 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?

Perhaps it's the tube that's vibrating. 

 - George 

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