Tell me about Deck Construction, Wet Decks - SailNet Community
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post #1 of 8 Old 02-18-2012 Thread Starter
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Tell me about Deck Construction, Wet Decks

I just got back from a midwinter trip to the boat and one thing on the list was to knock out the old mast wiring deck fitting. I was concerned that perhaps it wasn't installed well (well I knew that part) and that it may have leaked into the deck so I was curious to see what I would find. I snapped a picture of the result and I'd like help understanding exactly what I'm looking at.

First a bit more background. It's a 79' Contessa 26 and a survey this fall revealed my side and stern decks are pretty wet. All other areas checked out ok so I didn't necessarily expect a problem in the mast area but was skeptical that the fitting had actually stayed dry. This is a picture of the hole.

So, looking at the picture I have a few questions/comments. Note that the hole is probably ~0.75 - 1" in diameter .

1) I assume this clearly shows fiberglass, core, fiberglass and that the core is wood? But it doesn't necessarily look like a cross-section of plywood to me?
2) I'm surprised by how thick the fiberglass is in relation to the core. Both sections of glass are thicker than the core right? Is this normal and would this be consistent across the deck? Why exactly bother with the core at all at these relative sizes?
3) I know my decks are wet in the stern and I also know the boat sits a bit low in the stern (my waterline gets a lot of growth in the back). I'm guessing these things are related, is that reasonable? And is it common for wet decks to add noticeable weight to the boat?
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post #2 of 8 Old 02-18-2012
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The core is most likely end-grain balsa.. Plywood is an inferior core product because it enhances cross-migration of moisture along the plys, whereas balsa, being end-grain oriented does the opposite.. to a point. Pound for pound a proper skin/core/skin structure is stiffer and stronger than an equally engineered solid panel, and weight up high in the boat is counterproductive to stability, hence cored decks pretty well universal among builders. Moist decks can start to delaminate between skins and core, losing that inherent strength of the structure, wet core is not as stiff as the original dry either.

If indeed your boat is 'squatting at the stern' due to wet decks, that's a lot of moisture.. actually it's unlikely to be the cause - much more likely that it's the result of how gear and other things are stored aft.

Repairing truly wet decks is a big job, and an awkward job no matter how you approach it. Professionally done it may cost more than the value of the boat. As an amateur DIY project it's do-able but results can be all over the map.

Plenty of threads on this here already.. do a google search and SN threads are one of the first to show up...

Good luck..
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post #3 of 8 Old 02-18-2012
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Based on the photo, which shows a shiny surface all over the inside of the hole on the parts we can see, it would appear that the hole was properly sealed with some resin or other goop after it was made. This would tend to indicate that you don't have a wet deck/ delamination problem with this hole. If it's not due to this hole, there are obviously other holes or faults in the deck elsewhere - (shrouds? fairleads? cleats? handrails?) that are causing the issues aft and in the side decks. We had some problems with a long-term leak and subsequent delamination of an area about 2' in diameter. If I had actually squeezed out all the water from the core, it would have come to less than a liter. It doesn't take much to cause rot and delamination.
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post #4 of 8 Old 02-18-2012
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The apparent "squat" at the stern is not caused by water ingress to the decks. Do the calculations yourself. Measure the thickness of the balsa core aft, and calculate the weight of water that would completely saturate it. It will not be much.

Now take the same weight and add it to the stern.

You won't notice the ship squatting.

On my own ship, perhaps I have been lucky. The decks have leaked for 19 years, and probably well before that.

If they are not troubling you much, just leave them and live with it.
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post #5 of 8 Old 02-18-2012
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Just jab something pointy and sharp into the edge all around the hole?
If it is hard it was sealed and there should be no problem.
If it is soft it has leaked and rotted something out.
With some careful picking you may even be able to get a feel for how far the rot goes but almost always the rot goes further than expected.
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post #6 of 8 Old 02-19-2012
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Unless it is showing signs of being soft underfoot, just seal it and leave it.
Sail the ship.
Have fun with it.
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post #7 of 8 Old 02-19-2012 Thread Starter
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Quote:
Originally Posted by Rockter View Post
Unless it is showing signs of being soft underfoot, just seal it and leave it.
Sail the ship.
Have fun with it.
Yeah well that's the question I have. The advice I got from both the surveyor and the guy at the marina (who I could pay to fix it) both basically said "well it's a 30 year old boat, what do you expect?". Which seems to somewhat contrast advice here suggesting that decks should be fixed.

But I was questioning whether it's wise or worth it to seal everything up if I already know it's wet.

As another question why do manufacturers attempt to entirely seal the decks? It seems to be asking for trouble to keep water entirely out of a boat when, at least for the decks, they could perforate the inside and let the decks breathe.
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post #8 of 8 Old 02-19-2012
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asdf38

I also own a 79 contessa 26 so I I understand where you are coming from as it relates to this particular electrical fitting. I have had simaler issues and re-bedded it this past summer. I would suggest you start by using a dremmel tool to "router" out the wood core to determine if there is any real water penetration. The link below will describe what I am talking about better than I ever could.

mainsail's tutorial on re-bedding hardware.
Sealing Deck Penetrations to Prevent Core Rot Photo Gallery by Compass Marine at pbase.com

In my case the water had not penetrated in any real way and I was able to seal things up following the technique described by mainsail.

As to the deck/cabin top core on a co26. Mine varies in thickness depending on where on the cabin top you are measuring. Thicker around the mast base and thinner as you move back. As well The wood is plywood not balsa. I have read that the material used to core the deck and cabin top varies from year to year. So there is no "right" answer to what material was used.

You mentioned that the stern of your boat sits low. I have no reason to doubt that it is but if you would like to check it against other co26's it is easy enough. The boat has a design flaw built into it. The scuppers are about 3-4 inches to far aft. If, while docked or anchored, you have water collecting forward of the scupper, at the winch, then your boat is sitting about right. If on the other hand all of the water drains from the deck, thru the scuppers, again while sitting at anchor/dock then your boat is truly low in the aft end.

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