Above the waterline thru-hulls

[AJ_n_Audrey]

All, I have a 40-year-old Pearson, and the side-deck scupper, bilge, and cockpit thru hulls have started to crack (they're plastic). So I'm getting slight dripping from the cracks, and of course it will get worse. I'm replacing them with bronze, but I have a question: should I make a gasket to seal them against the deck or use 3M 4200? One of the through hulls is the thru-transom primary bilge pump fitting, so water never pools there (as it does on deck and in the cockpit with heavy rain or boarding waves) and my thought was to use a gasket instead of 4200 there, but maybe I'm missing something. So then I thought, why not use gaskets on all six? Other than the fact that someday the gaskets will need to be replaced, which argues in favor of 4200.

Thanks for your thoughts / experiences.

[GordMay]

Forespar recommends using a bedding sealant.
Forespar [Marelon] Instructions ➥ https://www.forespar.com/pdf/install...ng-seacock.pdf

[AJ_n_Audrey]

Thanks but these are not seacocks.

[pcmm]

Originally Posted by AJ_n_Audrey

All, I have a 40-year-old Pearson, and the side-deck scupper, bilge, and cockpit thru hulls have started to crack (they're plastic). So I'm getting slight dripping from the cracks, and of course it will get worse. I'm replacing them with bronze, but I have a question: should I make a gasket to seal them against the deck or use 3M 4200? One of the through hulls is the thru-transom primary bilge pump fitting, so water never pools there (as it does on deck and in the cockpit with heavy rain or boarding waves) and my thought was to use a gasket instead of 4200 there, but maybe I'm missing something. So then I thought, why not use gaskets on all six? Other than the fact that someday the gaskets will need to be replaced, which argues in favor of 4200.

Thanks for your thoughts / experiences.

the thruhull that is against the deck you want to seal from the top if possible. The last thing you want is the seal on the underside holding moisture up in the deck penetration.

If it were me I would do a few things. remove the old deck drain and dig out the core in that area (if it already has not been done) and seal with epoxy to prevent future core issues. When bedding the new fitting into the deck (effectively the deck drain) use butyl. That stuff never hardens and makes a great seal in this application.

for the bilge exit I'd worry less and just use sikaflex 291 to bed it. (similar to 4200)

[AJ_n_Audrey]

Thanks pcmm - is there a particular brand of butyl you favor?

Fyi, the area where the deck drain scupper go through are solid fiberglass as far as I can tell, but it's a good point, and I'll be ready with epoxy when I do this. The cockpit drains may connect to coring, but that area has already been renovated and balsa core removed and replaced with synthetic.

[Scrimshaw4]

Are you using bronze fittings or chrome plated bronze. I'd recommend SS for durability, strength and low maintenance. Bed them. JMHO

[AJ_n_Audrey]

What maintenance do you anticipate with bronze? They are not in contact with seawater. I'm thinking I won't live long enough to have to do maintenance.

[AJ_n_Audrey]

By not in contact with seawater, I mean they'll not be subject to any electrical current.

[tstano]

I found MainSail’s butyl tape the most reliable. https://shop.marinehowto.com/products

He has posted many DIY repairs for boaters.

[stormalong]

Plastic fittings lasted 40 years. Why not go with plastic again? Do you expect the boat to last another 40 years? Bronze will turn green and leave green streaks down your topsides.

3M 4200 will last a lot longer than buytl rubber exposed to the elements. Just don't squeeze it all out. Put in the fitting, put the nut down most of the way, wait a week before final tightening. Spraying with water accelerates the cure.

[mitiempo]

Plastic will live a short life with uv. Better choice is TruDesign which are Marelon.

https://www.trudesign.nz/marine/products

[stormalong]

Originally Posted by mitiempo

Plastic will live a short life with uv. Better choice is TruDesign which are Marelon.

https://www.trudesign.nz/marine/products

That is what I meant by plastic. Forespar or TruDesign will do the trick. I believe Forespar makes fittings for hose attachment. Don't know about TruDesign.

[CF32907]

CaptVR here,
Why not replace them with plastic as was put in place 40 years ago by the factory. The new formulations of synthetics are even better today. Or do you plan on being around in another 40 years.
As far as sealant. Any of the non permanent, types are acceptable for these fittings, and what a previous blogger wrote, I to like Butyl rubber sealant works great, expands and contracts with decks and fittings in the sun, seals excellent and for what ever reason, if you need to pull a fitting, they come out easily without a fight. Best place to find Butyl is in your standard building supply, mainly used for gutter joints, best part, $6. a tube.
I've surveyed boats for 30+ years, built 6 boats, wood and frp. Not a thing wrong with using plastic above the waterline. The only place I would use bronze or SS fitting is on the hull sides that could possibly be sheared off by a pilling's while moving. Most are protected from the rub rails, built up sheer strakes, spray rails, etc. For what it's worth, those are my feelings, If you got bucks to burn, use bronze or SS, keeps more people working than one mold machine.
Happy sailing all.... Capt. Vince Rakstis, Ret. MS St.Petersberg, Fl.
PS: My personal advice, any thru-hulls within 6" of water line on a power boat, or within 6" of water line at maximum heeling angle, I would install a vented loop to that discharge to prevent any back siphoning.

[mitiempo]

Originally Posted by stormalong

That is what I meant by plastic. Forespar or TruDesign will do the trick. I believe Forespar makes fittings for hose attachment. Don't know about TruDesign.

Guess you didn't go to the link I posted. It shows a full line of thru-hulls designed for hose.

As far as sealant you could use what TruDesign recommends for underwater use - thickened epoxy.

[Scrimshaw4]

Bronze is fine as long as you don't mind the green color tit turns after they've been exposed to salt air. Even happens to chrome plated bronze after a while. For deck mounted drains I'd recommend a removeable cover so you can clear the inevitable clogs. JMHO