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Old 03-11-2013, 07:30   #1
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Sea cock to Through Hull Threads

After doing a bunch of research on replacing brass ball valves with proper bronze seacocks, I think I have a solid action plan.

There is one remaining question. The marina I spoke to said they use 5200 to seal all underwater fittings. But the research I have done is that the threaded connection should not have 5200 on it. One day that valve may need to come off and using 5200 as a dope will make it impossible to remove. I did see one recommendation for 4200.

What is best practices for that joint? 5200? 4200? Other?

Thanks

Bill
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Old 03-11-2013, 07:33   #2
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Re: Sea cock to Through Hull Threads

4200 would be better. But a propane torch on the joint for a few minutes will easily loosen 5200.

David
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Old 03-11-2013, 07:43   #3
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Re: Sea cock to Through Hull Threads

NEVER use 5200 on anything that may have to be disassembled in the future!!!
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Old 03-11-2013, 07:47   #4
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Re: Sea cock to Through Hull Threads

I built a steel boat 20 years ago, and welded SS pipe sections to the 3/16" hull. (Very small SS bits are quite compatible with steel, especially with ample zincing nearby.) I used black Marelon valves, they are as slick, positive and tight now as they were 20 years ago. I can spin them off for inspection or replacement in seconds. If you have a metal threaded pipe attached to the hull, Marelon valves are hard to beat, if that is an option.
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Old 03-11-2013, 08:03   #5
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Re: Sea cock to Through Hull Threads

I would use 5200 to seal the head of the thru-hull to the hull on the outside and to seal the seacock flange to the mounting pad on the inside.

I don't know where the idea of using 5200 as thread dope came from, 3M doesn't advertise it for that use. A lot of people do use it as thread dope and as David said, it's pretty easy to break loose from metal if you heat the metal.

I don't think there is any advantage to using 5200 as thread dope but if regular pipe dope isn't handy, it should work.
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Old 12-12-2013, 16:06   #6
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Re: Sea cock to Through Hull Threads

1. I'd tend to go along with Captain465, and use 4200 for anything that you might want to disassemble and that includes the thru-hull to the hull connection. If you follow Mainsail's installation suggestions (Installing A Seacock & Thru-Hull Fitting In A New Location Photo Gallery by Compass Marine at pbase.com) and use 4200 or as he shows Sikaflex for both the hull install and the threads you'll be fine. In addition to any bonding values you'll have the locking power of a compression fitting.

2. As far as thread leakage goes, regular pipe dope will more than cover the maximum 5 lbs of water pressure you'd encounter.
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