[Public-List] Stern tube

David Fay davidfay999 at gmail.com
Sun Jun 7 11:08:17 PDT 2020

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 <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> wrote:
> David,
> 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,
> Gerard

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