Leak by the Shaft tube

[Maine Sail]

Short version: boat hauled out last weekend. The stern tube/log was corroded and broke into bits when I tried to tap it out. Got the boat out of the water in the nick of time, I guess. So had to take off the shaft (easy just by taking off the strut) and I'm having a new stern tube fabricated out of stainless for $50. It just bolts on to the hull and the dripless packing hose clamps onto it. I'm going for the 5200, permanent fix. Gob the stuff all around it and over it and it should last for forty years. Pictures will follow next weekend when I put it on.

Just be aware that stainless is usually not the best material for this application. Shafts are made from Aquamet/Aqualoy or Nitronic which is substantially less prone to crevice and pitting corrosion than 304, 304L, 316 or 316L.

The bronze used for seacocks and stuffing boxes would be more appropriate and it is called 85-5-5-5 bronze or eighty five three-five.. I suspect your log was simple brass or manganese brass with a high zinc content if it fell apart like that. you may also have a DC leakage problem on-board your vessel. I have never seen that happen to an 85-5-5-5 bronze and I have worked on many bronze seacocks out there with 40+ years on them. I have seen a manganese bronze prop literally disintegrate & fail on the same boat that has 85-5-5-5 seacocks and the seacocks showed zero signs of problems.

The best solution would obviously be to glass in a fiberglass shaft log then no worries about corrosion. If you do use SS inspect it often for crevice corrosion as the shaft log is an area that is VERY prone to oxygen starvation. This is especially true if using a dripless shaft seal that is not vented or a drips-less packing.

 

[Jim Legere]

All this discussion about failing stern tubes is making me nervous! Mine, from the outside, looking at the flange seems fine. Inside it can't be seen, it is incased in fiberglass and then the stuffing box hose covers that. Maybe I should unbolt and slide it out the shaft to be sure?

Ed, I don't think you need to worry. I had mine out 5 or 6 years ago when I replaced my prop shaft - it was in perfect condition and was Wilcox Crittenden or Perko (can't remember which) and very good quality bronze. As long as the hose between the shaft log and the stuffing box is OK, I think the H37C setup is bulletproof.

 

[Stephen Trapani]

Great information Maine Sail, thanks. I am planning on there being no crevices exposed. They will all be covered by 5200. My dripless is vented, with an open tube above the waterline. The only exposed portion should be the inside of the tube and portion inside the dripless gland. I do think I have a 12 volt leak and want to get that sorted before splashing next weekend. The shaft zincs don't last more than four or five months.

PS. The reason I'm using stainless is purely financial. The best estimate I can find for making it out of bronze is about $600, so $50 is a huge benefit to me in my current financial condition. I have the fantasy that I can still make it last a long long time by coating it with 5200.