[Public-List] Stern Tube Repair

Thu Aug 24 14:25:39 PDT 2017

George,
Thanks for your email.
Do you have any pictures of the stern tube once out of the boat?

If I build a new fiberglass stern tube the fiberglass tube will project
outside of the hull and receive the cutless bearing. so I wouldn't use the
casting.
This is a bigger job that I would like to avoid.
But I am worried that the clearance between the tube and the shaft is too
small: 3/16 or 1/4 all around the shaft sounds OK but that would require
the INNER DIAMETER of the stern tube to be at least 1-1/4. I measured the
OUTSIDE DIAMETER of the tube and it is 1-5/16, which makes me think that
inside it will measure 1 inch (schedule 40 pipe). If the tube is one inch
inside and does not move (the caulking supports it) then if everything is
aligned perfectly it would leave a 1/16 clearance, which means if the
engine moves more tan 1/8 the shaft would contact the tube.

I guess this is close fit is normal.

I had not thought of the tube vibrating... its very possible

is the inboard end of your tube rigidly fixed after re-bedding or can it
move a little bit?
how long is the hose in your stuffing box?
maybe my hose is too long or too flexible to keep the shaft centered?

Hernan

On Thu, Aug 24, 2017 at 12:48 PM, George Dinwiddie via Public-List <
public-list at lists.alberg30.org> wrote:

> Hernan,
>
> 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?
>
> Probably
>
> >
> > 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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