[Public-List] stern tube question

Michael Connolly crufone at comcast.net
Mon Feb 4 19:33:38 PST 2019


David, George and Clay,
This discussion and your observations have been very educational. I will keep a file of all this discussion. So if and when this might need to be done on #133 I will have the skinny on how to do it right. I was mistaken that the sealant around the stern tube was what kept the water out of the boat, at least from the aft end. I felt that with that greater surface area around the tube it would be the primary seal against water leakage versus the small surface area of the front side of the cutlass bearing housing. It makes sense to somehow try to lock the stern tube from rotating prior to unscrewing the cutlass bearing housing. If the stern tube hasn't rotated then one less thing to worry about. It looks like the points of alignment are the front flange of the shaft to the cutlass bearing. The stuffing box and hose just go along for the ride.
Thanks for all who contributed to this understanding and discussion.
Michael


> On February 4, 2019 at 5:33 PM David Fay <davidfay999 at gmail.com> wrote:
> 
>     Michael,
> 
>     You're going way beyond what I have experience with so I'm afraid I can't be much help.
> 
>     I can tell you that one of the accounts I read online of replacing a stern tube in an Alberg 30 said that it was hell trying to get the caulk out (Dolphinite? Thiokol? Something else?). I've also read of people using a hole saw to ream out the caulk or to drill a larger hole through the hull. But if you're lucky, your caulk hasn't hardened and you won't have that problem.
> 
>     I also wonder how your stern tube came to be dislodged. The stern tube is really an appendage of the cutless bearing housing with some support from the caulking around it. If it is dislodged, it is probably bent, the threads that hold it on to the housing are probably ruined, and the housing itself may be damaged. The prop shaft may also have been damaged if it rubbed against a bent stern tube. You may be looking at replacing many parts of the drive train.
> 
>     David
> 
> 
> 
>         > >         On Feb 4, 2019, at 4:40 PM, Michael Connolly < crufone at comcast.net mailto:crufone at comcast.net > wrote:
> > 
> >         David and George,
> >         I stand corrected. I was missing something. So from your good advice and photo references. I must assume that during fabrication Whitby assembled all together, bolted the cutless bearing housing onto the aft end of keel and then crammed in the Dolfinite around the stern tube.
> >         Does that make sense? Otherwise how would all this easily line-up with the stern tube fixed into the hull ahead of time?
> > 
> >         So with an older boat with a dislodged stern tube it would be best to start the process all over again. That is, remove the stern tube completely, scrape out all the accupucky, then assemble all the new components together with the stern tube slipped over the shaft. Align the engine to the cutlass bearing and then refasten the stern tube in place with new flexible sealant.
> >         Michael
> > 
> >             > > > On February 4, 2019 at 3:57 PM David Fay < davidfay999 at gmail.com mailto:davidfay999 at gmail.com > wrote:
> > > 
> > > 
> > >             [After writing the note below I saw that George had already replied to Michael and provided much the same information. I'm sending this anyway in case anyone finds it useful.]
> > > 
> > >             Hi Michael,
> > > 
> > >             Your understanding is not quite correct. The prop shaft needs to be concentric with the stern tube because the cutless bearing and its housing must be concentric with the stern tube (because the housing screws onto the stern tube). If the prop shaft is not concentric with the stern tube before the cutless bearing and housing are screwed on, then the prop shaft will apply sideways pressure to the cutless bearing wearing it out.
> > > 
> > >             It's also somewhat misleading to say the stern tube provides "a water tight passage for the prop shaft". Once the boat is in the water, the stern tube is filled with water. The water enters through two holes in the cutless bearing housing, passes through holes drilled through the sides of the cutless bearing by the installer (this step is skipped by some installers), and then travels aft to fill the cutless bearing and cool it down as well as forward to the stuffing box and its packing to keep them cool.
> > > 
> > >             Even if the holes are not drilled into the cutless bearing, some sea water will enter the cutless bearing from the aft end because the rubber lining that holds the prop shaft in place is grooved allowing a small amount of water to travel through the bearing, into the stern tube, and on to the stuffing box.
> > > 
> > >             A diagram or photos would be helpful here.
> > > 
> > >             David
> > > 
> > >                 > > > > On Feb 4, 2019, at 10:38 AM, Michael Connolly via Public-List < public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org > wrote:
> > > > 
> > > >                 Hello all,
> > > >                 It is my understanding that the stern tube was secured into the boat to provide a water tight passage for the prop shaft. There are no bearings in the stern tube on our boats. There needs to be enough clearance so the shaft does not rub against the tube, wearing a hole in it to cause a leak for sea water into the boat. No need for the tube to be absolutely concentric with the shaft as long as there is clearance for the length of the shaft inside the tube.
> > > >                 Michael
> > > > 
> > > >                     > > > > > On February 3, 2019 at 5:04 PM Clay Pass via Public-List < public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org mailto: public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org > wrote:
> > > > > 
> > > > > 
> > > > >                     I think that test assumes that there is not any play in the rubber cutlass
> > > > >                     bearing that might allow the shaft to hang low as it is resting on the
> > > > >                     bearing or it is pushed over to one side or the other because of wear in
> > > > >                     the bearing. I think that if you removed the cutlass bearing and housing
> > > > >                     you should have been able to visibly see shaft move off center in the stern
> > > > >                     tube as it was rotated.
> > > > > 
> > > > >                     On Fri, Feb 1, 2019 at 10:11 PM Kris Coward via Public-List <
> > > > >                     public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org mailto: public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org > wrote:
> > > > > 
> > > > >                         > > > > > > 
> > > > > >                     > > > > > >> As a note, my wobble wasn't visible. That said, it was detectable prior
> > > > > 
> > > > >                         > > > > > > to removal by uncoupling the shaft from the engine to test the
> > > > > >                         alignment, rotating the shaft by one coupling bolt, testing the
> > > > > >                         alignment again, and seeing that it was different. Once out, it was
> > > > > >                         confirmed by rolling the shaft down a reference flat surface (one of the
> > > > > >                         granite slabs at a machine shop, which are used specifically to make
> > > > > >                         sure that things are really flat, though I've heard that granite
> > > > > >                         countertops and mirrors also work).
> > > > > > 
> > > > > >                             > > > > > > > -K
> > > > > > > 
> > > > > > >                         > > > > > > 
> > > > > >                             > > > > > > > On Fri, Feb 01, 2019 at 10:01:12AM -0500, David Fay via Public-List wrote:
> > > > > > > 
> > > > > > >                         > > > > > > >>> Don,
> > > > > > 
> > > > > >                             > > > > > > > >>
> > > > > > >                             >> Thank you so much for your comments. It's not what I wanted to hear but
> > > > > > > 
> > > > > > >                             >> you've opened my mind to new possibilities.
> > > > > > > 
> > > > > > >                         > > > > > > >>> My initial thought was that there couldn't have been much force applied
> > > > > > 
> > > > > >                             > > > > > > > >> to the shaft because the wrap didn't stop the engine. Plus I have that
> > > > > > > 
> > > > > > >                         > > > > > > flexible coupling, which is supposed to avoid damage in just this kind of
> > > > > >                         situation -- the weak link as you call it. But we'll see. The next step
> > > > > >                         will be to see if the shaft wobbles when I rotate it.
> > > > > > 
> > > > > >                             > > > > > > > 
> > > > > > >                         > > > > > > >>> David
> > > > > > 
> > > > > >                             > > > > > > > Blue Teal #284
> > > > > > > 
> > > > > > >                             >>
> > > > > > >                             >>
> > > > > > >                             >>>> On Feb 1, 2019, at 9:39 AM, Don Campbell via Public-List <
> > > > > > > 
> > > > > > >                                 > > > > > > > > >>>
> > > > > > > > 
> > > > > > > >                                     > > > > > > > > > public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org mailto: public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org > wrote:
> > > > > > > > > 
> > > > > > > > >                                 > > > > > > > > 
> > > > > > > >                             > > > > > > > 
> > > > > > >                         > > > > > > >>>
> > > > > >                         >>>>>
> > > > > >                         >>>>>
> > > > > >                         >>>>> David:
> > > > > >                         >> You have probably bent the drive shaft with the dockline as I
> > > > > >                         >>
> > > > > >                         >>>>>
> > > > > >                         >>> suspect that is the weakest part of your drivetrain.. If you recall, Kris
> > > > > >                         Coward said he had a bent driveshaft and I have had one as well. The bend
> > > > > >                         in my shaft was about 0.005" and was small enough that the machine shop I
> > > > > >                         took things to managed to work that back to straight with a lathe and some
> > > > > >                         sideways pressure. Stainless is very malleable, and bends easily. I am
> > > > > >                         surprised though that you only have a 7/8" shaft for a diesel. They are
> > > > > >                         usually a full 1" because of the extra torque developed by diesels. It the
> > > > > >                         shaft did not bend, then the coupler probably gave because of that torque
> > > > > >                         or, if that did not fail, a motor mount has bent. You should have that
> > > > > >                         diesel on flex mounts. Whatever has been the resistance with the dockline,
> > > > > >                         it will have been the torque developed by your motor that will have caused
> > > > > >                         the weakest link to fail.
> > > > > > 
> > > > > >                         >>>
> > > > > >                         >>>>> Don
> > > > > >                         >>
> > > > > >                         >>>>>
> > > > > >                         >>> ---Original Message----- From: David Fay via Public-List
> > > > > >                         Sent: Thursday, January 31, 2019 9:21 PM
> > > > > >                         To: Alberg 30 Public List -- open to all
> > > > > >                         Cc: David Fay
> > > > > >                         Subject: Re: [Public-List] stern tube question
> > > > > > 
> > > > > >                             > > > > > > > Michael,
> > > > > > > 
> > > > > > >                         > > > > > > 
> > > > > >                             > > > > > > > That's possible of course, but this is not some ancient clunker of an
> > > > > > > 
> > > > > > >                         > > > > > > 
> > > > > >                             > > > > > > > 
> > > > > > >                         > > > > > > 
> > > > > >                     > > > > > engine but rather a new Beta Marine diesel installed just five years ago by
> > > > > 
> > > > >                 > > > > a highly competent boat restorer (Tim Lackey). I would be very surprised if
> > > >                 a rope wrap could twist the engine around on its engine mounts. But it's
> > > >                 certainly something I will have to look into.
> > > > 
> > > >                     > > > > > >>
> > > > >                     >>
> > > > >                     >> David
> > > > > 
> > > > >                         > > > > > > Blue Teal #284
> > > > > > 
> > > > > >                         >>
> > > > > > 
> > > > > >                             > > > > > > > On Jan 31, 2019, at 8:30 PM, Michael Grosh via Public-List <
> > > > > > > 
> > > > > > >                         > > > > > > 
> > > > > >                     > > > > > public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org mailto: public-list at lists.alberg30.org mailto:public-list at lists.alberg30.org > wrote:
> > > > > 
> > > > >                 > > > > 
> > > >                     > > > > > >>
> > > > >                     >>>>
> > > > >                     >>>>
> > > > >                     >>>> It sounds like the line wrap may have pulled the engine out of
> > > > > 
> > > > >                     alignment.
> > > > > 
> > > > >                 > > > > 
> > > >                     > > > > > >>
> > > > >                     >>
> > > > >                     >> _______________________________________________
> > > > > 
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> > > > > >                             > > > > > > > 
> > > > > > >                         > > > > > > 
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> > > > >                 > > > > Kris Coward http://unripe.melon.org/
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> > > >             > > > 
> > >         > > 
> >     > 
> 
 


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