Port and Hatch Sealant

[tdw]

Sadly the recent deluges in old Sydney town have exposed the failings of ageing sealant in some of my cabin ports and the forward hatch. No big deal, am removing all windows and hatches and will probably renew all the Lexan/methacrylate/whateveritis in both hatches and ports but do any of you lot have any thoughts on the best sealant to use. I havn't done this in 20 years when I just used a silicon, from memory, but thought maybe technology had moved on.

Any thoughts?

Thanks.

[Valiente]

It depends on where you're going, what the hatch material is and how long you want it in there. "Sealant" is generally thought to provide waterproofing, whereas caulk/bedding is meant to seal the barrier between some sort of rubber gasket stripping, the window and the frame.

I can get away on my old boat with silicone and gasketing, which conforms closely to the frame and leaves the silicone to do an essentially finishing seal. The new boat is an oceanic cruiser (or will be) and is 1/2 inch through bolted Lexan with what looks like a further 1/4" of sealant...it's hard..but you can mark it with your fingernail...and the fixed portlights don't leak. The pilothouse overhead one have auto-type compressible gasketing (rubber to rubber, soft) and they are beginning to fail.

Some pictures of the hatch type would help. I would bed the hatch frames themselves in something like 4200 or 291 caulk, dog down lightly on the bolts (which I would individually bed with caulk and back with thick fender washers inside), and then the portlights themselves would depend on location and material. Foredeck hatches will see more water and UV than something on the cabin sides, for instance.

[JomsViking]

I've had complete success with SikaFlex 291 for offshore (northsea) work, but boy is it nasty to apply I don't know if it can be used with "whateveritis", but it should be safe with Lexan
We've had a lot of rain lately, and we're starting to grow gills, but neither that, nor shipping seas find their way in.
I've also seen a lot of people using Butyl-Tape, especially on those constructions with Lexan windows bolted on without frames - and they also claim success with that. However I would personally NOT use that for hatches.

[sailingdog]

The butyl tape should work pretty well, but the lexan has to be mechanically fastened through it. Another option is neoprene gaskets.

[camaraderie]

TDW...yah...silicone is gonna be a problem on ports and hatches as it has low adhesion and will deteriorate over a fairly short amount of time. I ditto the recommendation of sikaflex291 or 3m 4200.

[sailingdog]

BtW, 3M recommends 4000 not 4200 for use with Lexan.

[JomsViking]

And some of the Sika's also MUST NOT be used with lexan. 291 is ok though.
The sealant also MUST stay flexible, as lexan has very different characteristic than wood and GRP. Many of the boats with lexan just bolted to the cabin have experienced that firsthand = fresh running water in the cabin

[Faster]

We have had good success with Dow Corning 795 - both as a sealant for in-frame ports and screw/bolt-on ports. It was recommended by a locally well regarded boat buider/repair yard. It is not a vinegar-smelling silicone.

It's a little hard to find - not generally in your marine or hardware stores - I get it from a local wholesaler. Not bad to work with and seems to have reasonably good adhesive qualities as well. It's about $10CDN/tube. We just redid the ports on our son's Ranger 29, it took less than 2 tubes.

[Valiente]

I've used some of those Dow products elsewhere...I seem to recall using their high-temperature stuff to seal an Atomic 4 head gasket. I like the idea of the price and the smaller tube size, as I always seem to have 3/4s of a typical tube left after I do a job, and it just goes hard and useless in short order.

[pigslo]

Hard and useless is not what your wife would say.