[Public-List] Stern tube

Gerard Kuperus gkuperus at hotmail.com
Sat Jun 13 20:02:30 PDT 2020


 Take a look at the picture on the site: http://www.alberg30.org/maintenance/MechanicalPropulsion/CutlessBearing_to_StuffingBox.jpg
Water can travel through the threads and cause a leak.

From: Clay Pass <clay.q.pass at gmail.com>
Sent: Saturday, June 13, 2020 7:42 PM
To: Alberg 30 Public List -- open to all <public-list at lists.alberg30.org>
Cc: Gerard Kuperus <gkuperus at hotmail.com>
Subject: Re: [Public-List] Stern tube

I don't think you need tape on the threads because a leak there would only travel to the inside of the tube and be stopped by the stuffing box.  As long as you caulk the tube/housing/hull interface there should be no leaks to the interior.  Am I wrong?

Clay Pass
#449 Seeing Deep

On Sat, Jun 13, 2020 at 2:42 AM Gerard Kuperus via Public-List <public-list at lists.alberg30.org<mailto:public-list at lists.alberg30.org>> wrote:
Here is a report on the haul out to fix the leaking stern tube.

I brought the boat over to the boat yard on Tuesday afternoon and was told that I would be second in line the next morning. I did a bit of prep work, such as unbolting the engine and figured I would have more prep time in the morning. When I arrived on Wednesday morning the crane guy greets my happily. It turns out the other people still didn’t show. The boat is on the dry a half hour later. After a quick power wash (bottom paint looks great!) I am disassembling things. One of the issues on my boat is that there is not enough clearance between the prop and the rudder to take off the prop, so I have to lift the engine and get it forward a couple of inches. After a few attempts I got it off the mounts and create enough clearance so that I am able to take everything apart. For some reason the coupler only moved a little bit, but I found that I was able to remove the shaft from the inside. By lunch time I was in pretty good shape. I took everything home to clean up. The tube was in overall good shape, with just a tiny bit of corrosion where it must have been touching the stuffing box. The shaft also has a bit of wear close to the stuffing box.

It was actually incredibly easy to take the tube out and as I cleaned out the inside I found out why: the thiokol, dolphinite, or whatever stuff was used, was very brittle and I pulled out a huge wedge of the stuff that had been embedded against the deadwood (to fix a leak one wonders?). I decided to fiberglass the tube in place on the inside, which I did after cleaning everything out, sanding, reassembling everything and putting the engine back in place (so that everything aligns). I managed to get the first layer of mat and epoxy in by 10 pm. A way too long day, especially in 85 degrees!

The next morning I took out the stern tube again (as I turn the fitting it popped right out of the fresh epoxy). One slight problem: I was unable to get the fitting from the stern tube. When I epoxied it up, it must have glued together. I started to caulk things up with 4200. There is a lot of space in there! When it started to fill up I also caulked up the bronze fitting and moved it into place and caulked up the bolts and tightened those up again. On the inside I could see how far the 4200 had travelled. At the front end I drilled holes on both sides in the fresh epoxy to add more there. Not surprisingly there was bit of a hole at the bottom (almost unreachable and invisible). After removing the excess caulking I added a layer of epoxy filler (epoxy with adhesive powde)r, followed by another layer of mat and epoxy. Looking good! After lunch I added a layer of 4200 (just in case) around the epoxy. Probably overkill, but I might as well finish that second (!) cartridge.

After checking the engine alignment I launched again by the end of the day. I did a quick check – everything dry. Motored back to the marina. Checked one more time and I see … WATER! Oh no! I am dumbstruck and my exhaustion after two days of hard work and a few weeks of planning is getting me down. Where does it come from? It turns out to be the rudder post. Thank goodness! I will tighten it up soon, but for the time being I dried everything and placed a sponge below the post. I checked one more time after dinner, and the next day: all good!

Besides the huge wedge of the grey caulking I found one other oddity: the stern tube and stuffing box are both 1 5/8” OD. I double and triple checked, but there was no way in the world a 1.5 inch hose would fit in that. It is an odd size.

My main purpose here was, of course to fix the leak, but I did not give myself a lot of time. I knew I should have taken another day. I got it done in two days as I really wanted to get the boat and myself out of the yard again. This is the only DIY facility open at this time (they actually never closed they told me and had the busiest season ever because people had time to work on their boats) and while the people there are great, it also a harbor full of liveaboards who are literally one step away from homelessness. Social distancing and face masks are optional at best and while I normally love to tell people that this is not a Triton (as they typically assume here in the SF Bay Area, where a lot of Tritons were built) but another Alberg design, it becomes a bit less attractive when you have to keep trying to physically distance yourself…

In any case, while the repair should last me for a while, I also think that sometime in the future I will replace the bronze tube with a fiberglass one, epoxy that in on both sides and also replace the shaft. With sour ribs and stomach, I don't really want to think about that, but if I had more time on the hard that is what I would do (I will not complain about the fact that we have no off season here).

Thank you again for all the excellent advice I received! I am very happy I got this fixed and instead of figuring it out on the spot, I knew exactly what to expect. There are always some surprises but you helped me to limit them to just a few.


From: David Fay <davidfay999 at gmail.com<mailto:davidfay999 at gmail.com>>
Sent: Sunday, June 7, 2020 11:08 AM
To: Gerard Kuperus <gkuperus at hotmail.com<mailto:gkuperus at hotmail.com>>
Cc: Alberg 30 Public List -- open to all <public-list at lists.alberg30.org<mailto:public-list at lists.alberg30.org>>
Subject: Re: [Public-List] Stern tube

Hi Gerard,

It did not occur to me that the threads needed tape or caulk (mine just had grease) but it makes sense. You really don't want water to escape through that joint.

But that wouldn't have solved my problem. My problem was that a big chunk of threads were missing from the end of the stern tube because someone at some time had sawn into them with a hack saw blade while trying to remove a cutless bearing. (A standard way to remove a recalcitrant cutless bearing is to cut it in several places from the inside with a hacksaw blade and then collapse it on itself.) There was enough of a hole in the threads on the end of the stern tube that water was able to escape the tube.

So why hadn't the stern tube been leaking ever since the hacksaw episode? I'm not sure but I think that when I was removing the bearing housing, I rotated the stern tube a bit and that may have sprung the leak.

I bought my fiberglass stern tube from Spartan Marine because I keep my boat at Derecktor Robinhood Marina and Spartan is right there. They also had a cutless bearing that fit the tube they had and installed it for me (did a nice job too). I don't remember the exact length of the tube but it was around 11 inches. You should measure your boat for the length and diameter of the tube you need. Its length will depend first on how far it sticks out behind the hull, which depends on how much room you have in front of your prop and how much room you want to leave for prop shaft zincs. It will also depend on how far it penetrates inside the boat, which in turn depends on where it needs to attach to your stuffing box hose.

The outside diameter of the stern tube will be determined by the hole in your hull that the bearing housing occupied -- in other words, the stern tube outside diameter will be the same as the outside diameter of the forward end of the bearing housing, the part that the stern tube screws in to (wish I had a picture). The inside diameter of the stern tube will be determined by the diameter of your prop shaft (usually 7/8") and how much clearance you need around it (the inside diameter of your old stern tube would be about right).

In all of this, I am assuming that you will replace both the stern tube and the bearing housing with a single fiberglass stern tube, like I did. There may be a way to replace just the stern tube with a fiberglass one and retain the bearing housing, but I don't know how you would mate the two.

In any event, it's not necesssary to get a fiberglass stern tube from Spartan Marine -- in fact, I'm not even sure they offer them in their catalogue. But there are plenty of other companies out there that do sell them. This may be helpful also: a step-by-step description of a stern tube replacement on a Pearson Triton by Tim Lackey with lots of good pictures: https://www.lackeysailing.com/archived/daysailor/rebuilding/systems/sterntube.htm

About glassing in the stern tube: that's exactly what I did (and what Tim Lackey did), even though some people warn against it (because it's too permanent, I suppose). If you do that, just make extra sure that you properly align the stern tube with the engine because it's going to be really hard to change the alignment of the stern tube if you get it wrong.


On Jun 7, 2020, at 1:22 PM, Gerard Kuperus <gkuperus at hotmail.com<mailto:gkuperus at hotmail.com><mailto:gkuperus at hotmail.com<mailto:gkuperus at hotmail.com>>> wrote:


Can you explain what the defect on the threaded joint was? Worn out, or? It is my understanding that the threads need tape and caulk and it is here where I expect I might have made a mistake when reinstalling. I put caulking on there, I remember, but no tape, and I also remember some going back and forth in order to line things up, which actually might have squeezed the caulk out.
Maybe that is wishful thinking... If I do end up replacing the tube, where did you buy it and do you have the dimensions? I might order it now, and have it handy in case I need to replace it.
Lastly, I am wondering why the stern tube is not glassed in place. Wouldn't that solve some of these issues?

All the best,


These businesses support your Association:
Please support them.
Public-List mailing list
Public-List at lists.alberg30.org<mailto:Public-List at lists.alberg30.org>

More information about the Public-List mailing list