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Old 07-27-2017, 02:47 AM   #1
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Thur Hulls

Hello all.

Attached picture. I have what I believe is bronze thru hulls mated to SS valve which is then connected to SS sea strainer.

Obviously not healthy. This must be dissimilar metal with moving water what is called galvanic corrosion? Most people I talk to suggest changing to SS thur hulls as the strainer is SS and I don't really want to replace.

Should the threads be sealed and with what?

Comments Appreciated.
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Old 07-27-2017, 05:07 AM   #2
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Most likely there is a thread miss match.

A thru hull has a straight thread , pipe and plumbing fittings require a tapered thread .

A thru hull underwater should never be just screwed onto anything.

A genuine seacock , bolted into the hull should be installed .

My preference is the old style tapered units that can be serviced for decades.
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Old 07-27-2017, 07:02 AM   #3
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I would start by hauling and disassembling everything. First priority would be to determine the level of deterioration in all the components.

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Old 07-27-2017, 07:55 AM   #4
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Yup, looks like tome to replace the thru hulls and valves with proper seacocks. Personally I would go with bronze.
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Old 07-27-2017, 08:02 AM   #5
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I second what FF said.
That valve looks more like galvanised or plated to me, NOT stainless! And, it almost certainly will have tapered threads.
You can't fix it properly just by cleaning it up and using some kind of sealant.
You really need to remove, inspect, and probably replace with a proper, UL approved marine seacock, like a Groco (there are others). Note that there is also no backing block!
Every boat I have looked at in the past two years, except one, had this same poor set-up. So, first on my list of things to do with almost any boat I purchase will probably be through hull / seacock replacement!
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Old 07-27-2017, 01:52 PM   #6
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That white crystal powder is most likely salt...from the threads not matching and weeping water through. I agree with backing blocks and seacock first, then whatever strainer or fitting needed.
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Old 07-28-2017, 08:57 AM   #7
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Groco sells flange adapters that will give you a proper thru-hull installation with the valve of your choice. I wouldn't mix metals, however perhaps using a Teflon grease or similar would help prevent galvanic corrosion. The adapter will give you the proper thread type and a sturdy installation, especially if you use one of their fiberglass backing plates.
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