Leaking marelan seacock on brass thruhull - SailNet Community
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post #1 of 35 Old 08-16-2008 Thread Starter
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Leaking marelan seacock on brass thruhull

Hi , I have a loose marelan seacock on a brass thruhull it weeps saltwater ocasionaly. the boat is in the water and Im hetting a little worried..
I tried to tighten it, but it wont snug up. There seems to be some kinda white gunk between the brass male thurhull and the female seacock, It looks like some kinda old glue and its dried out and crappy lookin..
Can I try to tighten this thing while in the water, or do you guys think I gotta get hauled out to do this. In and out is $300 ouch !
Ide hate to break up the white gunk while tightening, I could end up with a real leak.!
The thruhul looks pretty good so all I have to do is swap the marelon seacock for brass. right ?
Saildog was saying bad things about marelon on brass, IT makes sense that expansion - contraction would eventually ruin the glue..
Thanks for ANY help on this could post a pic...

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post #2 of 35 Old 08-16-2008
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If you can reach the thru-hull from the outside you can tap in a tapered plug and then change the valve. If you can't reach it you could have a hull diver install the plug; you change the valve while he cleans the bottom and then removes it when you are done.

I had a bad valve that I replaced using a tapered plug to block the thru-hull . It worked fine just weeped a bit; I had to be quick installing the new valve so the threads stayed dry enough for the thread sealant to work. I'm sure that someone will tell you to haul the boat and put in seacocks that are thru-bolted. If you can swap the valve while you are still in the water; you can buy some time before doing a more professional job.
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post #3 of 35 Old 08-16-2008
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You have...

You have mis-matched threads and should not have straight (what your thru-hull is) to tapered threads (which is probably what your valve is). Some earlier Marelon valves were also a straight thread which is what the thru-hull is and that will most likely never make a seal.

Furthermore bronze and Marelon should not be used together due to differing expansion / contraction characteristics. This is especially true of a male thru-hull into a female Marelon valve..

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post #4 of 35 Old 08-16-2008
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The problem may also be that the marelon seacock is cracked. That is fairly common as the metal through-hull will expand more than the Marelon seacock—which is why you shouldn't be using a female plastic fitting over a male metal fitting.

If the Marelon seacock is NPT thread, and cracked, and you attempt to tighten it... you'll effectively split it further, since the NPS through-hull will act as a nice wedge. Haul the boat, replace the through-hull and seacock with a properly installed setup. See Halekai's webpage on how to do it.

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You're right to be worried.

Haul the boat and fix the problem, being sure to install the proper components per HaleKai's website.

On a 23' boat, this shouldn't be a huge expense :-)

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BTW, I seriously hope the through-hull is BRONZE. You should never, ever use brass on a boat, especially below the waterline.

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thanks very much for the help guys ! , what I ended up doing was to use some of that tootsie role 2 part exopy stuff and basically cover the threads of the thru hull and about half way up the marelon seacock this seems to hold it for now, at least till next haul out, I dont understend how these things got so loose in the first place.. I guess the expansion contraction thing got the better of my seacocks ?
I wont be using Marelon ever again.....

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Sailbot-

Marelon is fine, if you use it with Marelon through-hulls. In some ways it is simpler to maintain, since you don't have the galvanic corrosion issues you have with bronze seacocks and through-hulls.

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Quote:
Originally Posted by sailbot View Post
I dont understend how these things got so loose in the first place.. I guess the expansion contraction thing got the better of my seacocks ?
They are mis-matched threads and were never meant to go together in the first place and that alone probably has something to do with why they are loose and leaking not to mention the use of differing expansion coeficients..



Quote:
Originally Posted by sailbot View Post
I wont be using Marelon ever again.....
It's not the Marelon! When used CORRECTLY it is, and can be, good stuff if cleaned & lubed yearly. Both Hinckley & Morris Yachts use Marelon but they also use the proper thru-hull which is also made of Marelon.

This is most likely what the two differing threads look like that you are trying to work with.

The threads on the right are a proper match NPT to NPT. The threads on the left are a VERY, VERY common mismatch NPS to NPT..

Your post is just more evidence why NOT to mix and match thread types and different materials bellow the waterline...!

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Quote:
Originally Posted by sailingdog View Post
BTW, I seriously hope the through-hull is BRONZE. You should never, ever use brass on a boat, especially below the waterline.
Except; that you can't find bronze pipe nipples anywhere. I've seen enough problems with plastic (marelon) valves that I would sooner use a brass valve (short term) over anything made of plastic.

Sailbot- I'd be cautious about that valve; if it is leaking without being able to re-tighten it for fear of failure it really should be replaced. If you put a brass or bronze ball valve on top of your bronze thru-hull it should be fine until you decide to haul-out and do a better job. I know this is contrary to what "the experts" here are saying but my boat has the original bronze thru-hulls with bronze ball valves on top of them (PO replaced original plastic gate valves) and there have been no issues with them; and everything is fine. Thread engagement when tightened is ~2x what is shown in the cutaway photo...
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