Sealing through hulls in balsa cored boat - SailNet Community
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post #1 of 16 Old 04-05-2013 Thread Starter
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Sealing through hulls in balsa cored boat

Ive recently purchased a dreadnought 32 with a balsa cored hull. There are two gate valves in the head that are fairly corroded and have me a bit concerned. Im planning to haul to boat out and remove these Valves as well as glass over the thru hulls. My reserach has found that a 12-1 taper is to be ground into the edge of the thru hull in order to prepare it for glassing. My question is how to put this taper into the holes when there less than a foot apart and if its a differnt proccess to glass over a through hull thats into a balsa core. Ive done a bit of deck repair already with polyesther resin. but nothing under the waterline like this. I want to make sure I do the best job possible so any advise anyone could give me on what materials to use and how to go about it would be a great help. Thank you much.
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post #2 of 16 Old 04-06-2013
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Re: Sealing through hulls in balsa cored boat

LiveIt,

The 12:1 is probably referring to the thickness of the fiberglass so if it's 1/4" thick, taper it 12/4 or 3" to each side. This allows the application of a series of circles of fiberglass that increase in size each sequential layer until they reach full size. Before you do this, plug the balsa hole with filler and be sure to taper both inside and outside holes properly.
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post #3 of 16 Old 04-09-2013
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Re: Sealing through hulls in balsa cored boat

liveitwell, grind out your 12:1 the best you can with the room you have. If you want you can even sand down that stringer (just enough to get the paint off) and put a piece of cloth that overlaps that. Basically, the 12:1 is best case senerio. I only had a 6" diameter area to work with a hole that was 3/4"-1" thick, so my bevel turned out to be 6:1 roughly. 4 years and countless waves, and it doesn't leak a drop. I just beveled it from the inside.

I understand what the book says and why it says it, but sometimes you have to do the best you can w/ what you got.

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post #4 of 16 Old 04-09-2013
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Re: Sealing through hulls in balsa cored boat

The core should be handled like you would a penetration of the deck core: take the coring back between the glass layers, seal the coring edges with thin epoxy, then replace the coring with thickened epoxy. Now glass over.
There's a good illustration of this here: http://www.wbryant.com/StellaBoat/index.htm
Go to the "Haulouts" tab.

Mark Smith
1977 C&C 30 Mk 1 hailing from Port Clinton, Ohio

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post #5 of 16 Old 04-09-2013
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Re: Sealing through hulls in balsa cored boat

I'd use epoxy as it has better adhesive qualities than polyester.

You may find this article useful: Sealing Deck Penetrations to Prevent Core Rot Photo Gallery by Compass Marine at pbase.com

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post #6 of 16 Old 04-10-2013
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Re: Sealing through hulls in balsa cored boat

Hi

West Systems has great online resources (and many mentions of cases like yours)

Forum wont let me post url -- but go to westsystem.com / ss / use-guides
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post #7 of 16 Old 04-10-2013
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Re: Sealing through hulls in balsa cored boat

Go to epoxyworks.com for comprehensive answers to this question. Then: Articles by subject; Boat repairs and restoration;Repairing machined holes in fiberglass. Epoxyworks is a West pubblication.
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post #8 of 16 Old 04-10-2013 Thread Starter
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Re: Sealing through hulls in balsa cored boat

Thanks for the info folks, keep it coming its a great help! Ive got a better idea of how to go about it now. Ive also been doing lots of tapping to try and detect any delamination, tricky below the waterline. Seems like it might not be as bad as I imagined, though i can be an optimist... Any more info is welcome you folks are great, thank you.
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post #9 of 16 Old 04-10-2013
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Re: Sealing through hulls in balsa cored boat

I may be completely out to lunch here - , but the engineer in me says the 12:1 should be on the outside!
Logic tells me the pressure is pushing outside ->in when the boat is in the water. So shouldn't the wedge be on the outside so water pressure tends to hold the plug in place more firmly?
Never done this, but that would be my first thought.
Sam :-)

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Re: Sealing through hulls in balsa cored boat

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Originally Posted by Liquorice View Post
I may be completely out to lunch here - , but the engineer in me says the 12:1 should be on the outside!
Logic tells me the pressure is pushing outside ->in when the boat is in the water. So shouldn't the wedge be on the outside so water pressure tends to hold the plug in place more firmly?
Never done this, but that would be my first thought.
Sam :-)
Hopefully you're not relying on water pressure to hold anything in place. The 12:1 feather is to get good bonding of the new glass to the old, so you want it on both interior and exterior.

Mark Smith
1977 C&C 30 Mk 1 hailing from Port Clinton, Ohio
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