Sealing portlights

[IguanaSwim]

We have a 40 year old sloop that has port lights below deck that leak on high seas. We are thinking of caulking them with 4200, rubber gasket against stainless. We never open them and they have never stopped leaking despite being cranked down all the way. Is 4200 the right stuff? Is the notion harebrained?

[Benz]

Should work. 5200 will as well, as long as sunlight doesn't get to it for too long.

[IguanaSwim]

Thank you. We feel better about sealing them now.

[tkeithlu]

Butyl tape is the usual bedding recommendation for port lights. If you use 3M 5200, first say clearly with your right hand raised "I never, ever, want to open this port again, and neither will any future owner."

[JoeRobertJr]

Are we talking about sealing the portlight frame against the hull, or sealing the part that opens against the frame when it is closed?

We are having trouble with the latter. The rubber gaskets are somewhat dried and brittle. We are about to undertake replacement of those.

[IguanaSwim]

Am talking about making sure they are completely closed. 4200 isn’t as eternal as 5200. We’ve also lost a dog on a few and so are relying on three to keep it closed. We are crossing seas and can’t have a leak or a blow out. Butyl is great but not strong enough.

Farther aft we want the option to open them. We cleaned then lubed with silicone grease. Apparently vasiline damages the gaskets.

Thanks all for the help!

[Glenn.Brooks]

So you really need the port lights? One option is take them out and glass over the holes in the hull. Nothing better than that for keeping water out.

Alternately, try Dolphinite bedding compound to seal up the frame. Dolphinite is the traditional method for bedding wood members, plywood, deck fittings etc. it works wonderfully, cleans up easily and lasts 40+ years. Much more effective than 4200 or butyl tape.

Imbedded every screw, deck fitting and all portholes with Dolphenite on my last boat .- an alberg 30. The next owner sailed it across the pacific, from SF to the Phillipines and never took on one drop of water from a leak. Been using it on boats since 1970. It’s really good stuff.

[Bowdrie]

The Op says, "Rubber gaskets against stainless".
I presume that is the gasket that seals the opening frame against the hull mounted fixed frame.
There are at least a billion different O-rings made from several materials and in sizes from microscopic to measured in feet, and of a wide variety of thicknesses.
Take one of the opening parts to a company that deals in seals, they will fix you up with something that will fit and won't leak.
Also, the above post about Dolphinite is spot on.
It truly is a product that anyone with a boat should have a can on board.
It ain't just for wood, hint, once you open it you want to make d#*n sure that the lid goes back on cleanly, and store the can upside down.

[Bowdrie]

Addendum.
Something I'll add, while you have the opening section(s) removed, see if you can lay a piece of glass, (or other FLAT piece of something.) against the hull mounted section that the opening frame closes against.
Far too many portlights, (of whatever shape, along with hatches,) get installed on curved surfaces by ignorant people who know no bounds when it comes to tightening the bolts on such hardware.
The hardware frames get twisted/warped/bent out of plane, and never seal properly once the original soft gasket gets some age on it.

[Rumrace]

I’ve heard of this other product but I carry Lexel for emergency of permanent fixes.
If you need fresh fat gaskets for old frames and the hinge and pin are healthy you can print them in TPU
You can supply a drawing of the gasket go onto cults3D.com ask for local printer familiar with TPU. It’s like modern rubber and you can program it’s density and compression. UV chemical fuel proof very durable. You can buy sheets of TPU or TPE but you are looking to replace a puffy gasket with no seam.