stern tube material

[margitchris]

I've decided to change my Seafarer's crazy external stuffing box ( yes, mounted on the outside of the hull necessitating diving to adjust and further needing a liberal leak rate to lubricate the cutless bearing) to the traditional flexible type. No stern tube protrudes inside the hull, so I expect I'll have to fit one. I know fiberglass ones are available or can be made up. My question is: wouldn't stainless steel or brass be a better material from the standpoint of cutless bearing set screws. Would one find stainless or brass tubing of the appropriate inner diameter and perhaps have hose barbs machined into the end?
Chris Miller
Seafarer 31 yawl

[Quetzalsailor]

Amazing! Just shows that we're still young, when we hear something new. Surely some other Seafarer has that setup...

Anyway, bronze is more like it for a stern tube; brass is absolutely the wrong stuff below the waterline. Some boats have fiberglass stern tubes; I recall no chatter about problems with setscrews. The bronze stern tube in our '72 Morgan 27 was knurled on the outside and worked to bond to the polyester filler that retained it in place.

There are two 'normal' setups for this problem. One has a pair of castings bolted through the trailing edge of the keel, the outer half carries the cutless bearing and the inner half carries the stuffing box. In this case there is a hole or pair of holes through the sides of the keel which admit water to the space between the cutless bearing and the stuffing box. The other setup has a stern tube which extends into the boat and carries the stuffing box; the shaft is unsupported until it reaches aft to a strut with the cutless bearing.

The best part of what you plan to do is to eliminate the stuffing box and install the dripless shaft seal.

[Tim]

Wow! That sounds like even more of an oddball arrangement than the original sliding, greased shaft setup on some of the Albin Vegas. Do you have pictures of your setup? I've never seen anything like that.

You typically find stern tubes of either fiberglass, or bronze. I don't recall ever seeing a stainless stern tube. Bronze fittings are generally bolted and sealed to the hull on one side, and do not pass directly through in one piece. I think the difficulty of guaranteeing a sound seal around a metal tube in a fiberglass boat may have something to do with the typical use of fiberglass tubing: you can successfully bond fiberglass to fiberglass without worry, assuming you go about it correctly. Fiberglass bonds to any metal are always a bit suspect, though it can be done. I'd rather have a fiberglass tube myself..

There are a variety of precast bronze stern tube fittings available, but you have to determine whether they will work on your boat, depending on the sort of aperture you have and how much room you have inside the keel deadwood at the other side.

My guess is that you'll probably find that a fiberglass tube makes the most sense. They are readily available in a variety of sizes to match common Cutless bearing and hose sizes, and are not that difficult to install.

Setscrews will last a long time threaded into a fiberglass stern tube; should the holes become enlarged over 40 years' use, it's a cinch to repair the old holes and drill/tap new ones. But they really only fail on boats that have been poorly maintained or neglected, usually exacerbated by poor installation in the first place.