Replacing Through-Hulls

While I'm redoing the transom on my 20' aluminum boat, I would like to go ahead and replace some through hulls. There are 3, one for the drain, and two for the livewell. The drain is not the plastic replacable type. The livewell through hulls, one 3/4 and one 1 1/8, are though. West Marine sells some that are white plastic and about $15 for the larger size. My local hardware store sells some white plastic "Attwood" models for about six bucks. The package does say they are not for below the waterline applications. Maybe a dumb question, but is Attwood just covering their butts and their through hull is just fine for that purpose, or do I have to spend three times as much to get an identical looking model that doesn't carry that warning? Also, do you simply goop some 4200 or 5200 around the hole to bed the through hull before tightening it down, or is there more of an art to it? Thanks for your replies.

Re: Replacing Through-Hulls

Ya, I think a lawyer came up with that one.

They will be fine with some 3M on them, my question would be, why do you have drains below the water line?

Re: Replacing Through-Hulls

Thru hull fittings are not the place to skimp. A failure of a thru hull can put you on the bottom without warning.

Don't assume that all "plastic" thru hulls are the same. Thru hulls are made from both plastic and Marelon. Marelon is rated UV stabilized and is rated for use for both above and below the water line. White plastic is well....white plastic.

Ideally, any thru hull below the water line should be bronze and backed up with a seacock.

About Marelon?
Marelon? is a proprietary formulation of polymar composite compounds using DuPont resins and additives to produce a superior marine-grade product.

For use above and below the waterline
Precision molded plumbing systems
Complete freedom from corrosion
U.L. and A.B.Y.C. approved
Forespar "93" series valves and thru-hull fittings meet all design criteria and exceed all mechanical property requirements specified by the International Standards Organization

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Re: Replacing Through-Hulls

I fully agree with dingbat. His info is right on the money. Does your boat really have thru-hull fittings below the water line? Or did you bring that up because of what was written on the package?

I personally prefer stainless thru-hull fittings over plastic or brass. Although brass is very tough stuff, when its chrome plated, it is just one more thing that can get crappy looking. At least with SS, it can be polished when it dulls.

When you look for fittings, be sure that the mating surface of the fitting has a recess cut in it to hold sealer. Also, for your aluminum boat, some of the stainless steel fittings come with nylon "gasket" that will prevent any galvanic action between the SS and aluminum.

And don't skimp on the hoses either. Skip the cheap corrugated plastic hose and get vinyl or the Sheilds brand live well hose.

Re: Replacing Through-Hulls

Mark42 said:

I personally prefer stainless thru-hull fittings over plastic or brass. Although brass is very tough stuff, when its chrome plated, it is just one more thing that can get crappy looking. At least with SS, it can be polished when it dulls.

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Brass has absolutely no business being used on a boat. Brass an alloy of copper, tin and zinc with zinc making up to 30% of it's content. Zinc is the same material used on your outdrive for it's sacrifical properties.

Only bronze fittings, copper and tin, should be used.

Stainless should not be used below the water line due to possible problems with crevice corrosion.

Re: Replacing Through-Hulls

dingbat said:

Brass has absolutely no business being used on a boat. Brass an alloy of copper, tin and zinc with zinc making up to 30% of it's content. Zinc is the same material used on your outdrive for it's sacrifical properties.

Only bronze fittings, copper and tin, should be used.

Stainless should not be used below the water line due to possible problems with crevice corrosion.

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Ops, I wrote brass, I meant bronze. My bad.

My personal opinion is that Crevice Corrosion is for all practical purposes imposable on a properly installed stainless steel fitting. And bronze is not immune from the crevice corrosion either. In a below water line situation, if properly sealed, the environment for crevice corrosion to occur just doesn't exist.

I'm not going to say that crevice corrosion never happens, but even if it does, the result is just a slow drip leak that will eventually be found, and chances of a catastrophic failure are slim. And take into account that most of the boats members here have are not sitting in the water 24/7, and the opportunity for any corrosion is slim. Just think when was the last time someone here reported that any metal through hull fitting corroded and failed?

Like I said, thats just my personal opinion from personal experience. Maybe CC is a bigger problem in other locations.