Best underwater sealant?

[TitanTn]

I'm a new Supra owner as I just purchased a 1986 Saltare. Needless to say, my project list is very long and I'm going to be tackling it one project at a time. So, for my first question:

I'm going to rebed the Supertrapp exhaust tips to the transom. What sealant should I use? 3M 5200 sealant is a "permanent" bond. I wouldn't think that's what I want. Tips on the best sealant to use?

Thanks!

[beast 496]

If you do not want it to leak use the 3m 5200. Fast set is easier to work with. The standard 5200 takes up to 7 days to fully cure. For under water installes this is what I use exclusivly. For above water line, anywhere sun can emite UV I use 3M 4000. Al

[DKJBama92Mariah]

I agree with Al.

5200 without a doubt.

[wotan2525]

I didn't trust the 5200 on the exhaust as I have never seen any information about it's heat resistance. I used black RTV and it seemed to work great.

[TitanTn]

I didn't trust the 5200 on the exhaust as I have never seen any information about it's heat resistance. I used black RTV and it seemed to work great.

I wouldn't think there'd be a lot of heat back there in the water.

I think I'm going to give the 5200 a try. Is this something you can get at home improvement stores or is it a speciality marine purchase?

[DKJBama92Mariah]

It's a marine product but my local wal-mart carries it. The problem is, my wal-mart only sells it in smaller squeeze tubes that end up making a horrible mess; it is just too thick to squeeze out easily. I buy mine in a caulk gun tube at my local marine dealer. I think it was $21.99 when I bought a tube back in July. From a websearch on the subject I think I recall reading somewhere that Home Depot carries it. You might check that avenue if you don't have a local marine dealer with a good parts counter.

AT ALL COSTS, avoid getting this stuff in your hair. I've relearned this lesson time and time again and it doesn't seem to take. It never fails that i end up touching my head and end up making an unplanned visit to the barbershop. I would suggest wearing an old ball cap you don't care about and turn it around backwards to cover the back of your head. I really hope I remember to do this next time I mess with the stuff.

wotan,
I'm not going to argue with your concerns over heat nor your choice of sealant. The heat concern certainly has merit. It is a fact that pretty much all the waste heat of the engine (from both the exhaust gases and engine cooling water) exits through those two critical thru-hulls. When the boat is underway and on plane, the exhaust outlets are out of the water and at the same time, the engine is producing a whole lot more heat than at idle. At the same time though, the raw water pump is pushing a whole lot more water through the system to cool things off. No doubt the fittings get hot, at WOT with 90+ degree river water temp, I bet they might get to 250 or even 300 degrees Fahrenheit. Any more than that though and you'd be seeing MASSIVE amounts of steam from the exhaust. I'm reasonably sure that this is within the limits of 5200.

For many years I have read and followed several boating forums, and I can't recall ever reading of anyone using anything but 3m 5200 or 4200 for underwater exhaust thru-hull fittings. I'd think that if there was a problem with exhaust heat, we would have heard of it by now.

From the Permatex website Black RTV is suggested for "Valve covers, oil pans, intake manifold end seals, timing covers, transmission pans." I'm not going to argue my point further because the OP has already made up his mind and because you of course are free to do as you wish with your own boat.:) As you said, it works and is keeping the boat watertight.

Titan, don't forget the ball cap.

Cheers,
DKJ

[DKJBama92Mariah]

Titan,

On a side note, what precisely is the reason for rebedding? Is it just preventative maintenance or are they leaking? Also, is there any looseness involved? If they've been leaking for a long time or are loose, you could have rot issues. You won't know for sure until you get it taken apart, but hopefully everything is solid in there.

DKJ

[TitanTn]

Thanks for all the info. My goal in rebedding is that it looks like it hasn't been done in a very long time and I want to check the condition of the thru hull once I pull the outer plate off. My goal is to check it out, for everything to be perfect, rebed the plate and check that one off my list.

It's a new to me boat and I need to get to know her. She's really in good shape, but I have a long list of small things and a couple medium things that I want to get accomplished.

Thanks again.

[DKJBama92Mariah]

Sounds like you've got the situation under control. Keep us posted on your progress and post some pics as you work through your resto project.

BTW, I just noticed you are a new poster. Welcome to the forum!

Cheers,
DKJ