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DwayneSpeer 12-22-2008 07:18 PM

Sealing my shrouds
Any advice on how to seal the deck penetrations where the SS metal members go thru the deck and connect my shrouds to the knees below deck?

I have an old teak decked boat with a balsa core and the penetrations where the shrouds go thru have leaked ever since I bought the boat. The configuration is as follows. The knees are very beefy and bring the shroud attachment inboard about 15 inches from the hull. There is a four inch wide by 3/8 inch stainless steel flat stock member that attaches to the knees and goes thru the deck and the shrouds attach to that. The hole the flat stock goes thru is far bigger than it is due to the poor boat building practice. It has about 1/2 inch clearance on all sides. I've tried the West Marine caulk and it just doesn't work. I think I need a good flexible caulking that will stick well to the metal as well as the wooden parts. Any suggestions?

Fortunately I live in a near desert climate and it only leaks when it rains. :rolleyes:

timebandit 12-23-2008 04:12 PM

You might try to fab a stainless cover plate that will fit with much less clearance.

Maybe one of wood that sheds the water away from the flat stock.

Then use clear silicone to seal the smaller gap.

I use silicone and the boat has not leaked there for 5 years.

merc2dogs 12-23-2008 05:02 PM

open the holes up a slight bit so you have more room. then attach a decorative plate on the underside and fill the hole from the top with suitable caulk, then put a cover over that and seal as normal.

tighter fitting holes provide less area for water ingress, but caulk works best if it has some play room, a wider strip of caulk can stretch quite a ways without splitting or tearing free. Once it splits it's a leak.
It's not a problem on stationary items, but everything bolted on to a boat moves.
stay away from caulks that dry hard.


mike dryver 12-23-2008 05:07 PM

before you even consider sealing the deck you should check to see if your core is wet and your chain-plate holes that's what those things are called. you can use a moisture meter for this as well as removing the old caulk around plates and in contact with hull material. with that much room you should be able to stick a thin blade screw driver or even paper towel to make contact with core and see if it is wet. if wet you must find out how far in it goes and dry it out (sealant will not adhere to wet/damp core or metal). then ream out core around plate holes and fill with epoxy etc. find threads on this here in archives or other sight. you should remove plates for working room and also to to make surrounding holes smaller if possible so less caulk is needed and also so plates won't move as much which sounds like your prob. if continuously leaking. and then have cover plates made to go over chain-plates with small clearance around chain-plates. i would not use silicone as it does not adhere well to anything it really only makes a gasket. you should use a poly-sulfide to fill around chain-plates and put cover plates on when poly is freshly put down to bed it i would also make an inside cover plate unless there is a wood trim piece that fits around chain-plate.

mike dryver 12-23-2008 05:25 PM

first you have to find out where the water is coming from the chin-plates or the deck or both. you should without a doubt dry the core if wet or nothing will stick to it no matter how much sealant you put in the holes and silicone is not really a sealant as much as a gasket forming material so it will only work for a short while especially if you have such a large gap around your chain-plates. if core is wet you need to dry it and at the least seal the core edges with a penetrating epoxy. this would require you to remove the chain-plates for access. i would have a sheet metal or machine shop make cover plates that go over your chain-plates with a small clearance around chain-plates. so when you put them on the wet sealant(poly-sulfide) it will ooze out around the edges and in-between the plate and chain-plates. check other threads on subject here and other sites

mike dryver 12-23-2008 05:26 PM

dis-regard 1st post thought it went into twilight zone and did not address possible deck leak issue

timebandit 12-23-2008 08:57 PM

This is what I have


Originally Posted by timebandit (Post 422015)
You might try to fab a stainless cover plate that will fit with much less clearance.

Maybe one of wood that sheds the water away from the flat stock.

Then use clear silicone to seal the smaller gap.

I use silicone and the boat has not leaked there for 5 years.

sailingdog 12-24-2008 06:18 AM

Don't use silicone... Silicone caulk really has no place on a boat. What you should probably do is make the gap around the plates a bit smaller by filling the excess gap with thickened epoxy. The gap shouldn't be 1/2" all-around. Bringing it down to 1/4" would be a good idea. If the chainplates flex more than that, you've got other problems to worry about. While you're at it, checking to make sure the deck is sound in the area, especially if the chain plate passes through a cored section of the deck, would be a really good idea. If the core is exposed, sealing it with thickened epoxy would also be a really good idea.

Making a stainless steel cover for the slot is a good idea. Make it out of the same grade stainless steel as the chainplates if you can.

Use SikaFlex 291, 3M 4200, or butyl tape to bed the stainless steel cover and seal the hole.

DwayneSpeer 12-24-2008 02:10 PM

Thanks guys. I'll take your advice to heart.
timebandit... If my shrouds looked that good I'd be thrilled.

Also, I've decided to refurbish my entire deck this coming summer. More to come!!!

Capnblu 12-24-2008 03:46 PM

Dwayne, use butyl. You will have a much easier time removing and dealing with it. In my own experience it has not hardened in 30 years where the PO hadn't touched it. It remained flexible and well adhered. It can easily be cleaned up with a scraper and a rag wetted with acetone. Can't say the same for sikaflex. Butyl tape can be found at glass shops. Like most things your prep should take 80 to 90% of the time. Keep all pieces clean of all oil, dirt and water, and you will be well on your way to a dry bilge. There are plenty of posts outlining scenarios you may encounter as you refurbish your deck. Good luck.

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