De-lamination, Who Is Kidding Who?

[Neo]

I'm sure there is truth to the idea that wet decks are not so bad as long as there is no de-lamination. Those of us with wet decks find comfort in the notion, and those selling boats with wet decks perpetuate the idea. Well, it may be true but not if the deck is cored with plywood.

We cut open a small section of deck under the anchor cleat, and to our surprise found a piece of plywood. The very top layer of the plywood was firmly affixed to the fiberglass (no delamination) but the plywood underneath was rotted mush.

"Dad, the boats falling apart. It's OK son, as long as we don't have dalamination." Ha, ha.

One caveat. The section we cut open also had balsa which bordered the plywood. It was not rotted nor delaminated.

[Rhapsody-NS27]

Originally Posted by Neo

One caveat. The section we cut open also had balsa which bordered the plywood. It was not rotted nor delaminated.

Was there was some epoxy separating the balsa and plywood? It might have helped keep water from spreading. Hopefully the repair goes well for you.

[noelex 77]

The structures strength is severely compromised by delamination or deterioration of the core.
It is composite structure and any loss of the mechanical properties will compromise strength.
Plywood is commonly used around fittings. It is a poor choice. It seems much more prone to rot than end grain balsa.
Around fittings the deck should be replaced, by the manufacturer, with a solid
fibreglass core.
A few dollars in construction costs will save a lot of heartache later. If additional unexpected deck fittings are required the core around the screw holes should be replaced by solid epoxy (see the west system guidelines)

[colemj]

This is common construction for the time (and even now in a lot of cases). Balsa does not have the compression strength required for under loaded fittings, so plywood inserts were used. Replace with solid glass layup or epoxy mixed with glass chop and cabosil instead of plywood.

Mark

[Neo]

Thanks for the comments.

I haven't had the time to remove all the core and determine how much more deck needs to be removed.

I was planning on replacing the plywood with balsa to avoid "creating hard spots that could effect the designed stress load patterns". Now I'm having second thoughts.

How large an area of solid epoxy is required to withstand compression?

(A friend made a similar repair with solid epoxy and lost his boat during a storm when the anchor cleat, along with the solid epoxy base were ripped from his deck).

[minaret]

Originally Posted by Neo

Thanks for the comments.

I haven't had the time to remove all the core and determine how much more deck needs to be removed.

I was planning on replacing the plywood with balsa to avoid "creating hard spots that could effect the designed stress load patterns". Now I'm having second thoughts.

How large an area of solid epoxy is required to withstand compression?

(A friend made a similar repair with solid epoxy and lost his boat during a storm when the anchor cleat, along with the solid epoxy base were ripped from his deck).

Replace the rotten ply with Coosa board or equivalent. Problem solved. A moisture meter would help you determine the extent of the affected area without drilling exploratory holes. I prefer the JR Overseas GRP-33. An awesome tool.


Wood and Composite Moisture Meter GRP33 - Amazon.com

[Neo]

Originally Posted by minaret

Replace the rotten ply with Coosa board or equivalent. Problem solved. A moisture meter would help you determine the extent of the affected area without drilling exploratory holes. I prefer the JR Overseas GRP-33. An awesome tool.


Wood and Composite Moisture Meter GRP33 - Amazon.com

Coosa board. I'm feeling it.

[minaret]

Originally Posted by Neo

Coosa board. I'm feeling it.

Excellent. Order early. I recently made a huge order for a client and they had to scrape together all of their 1/2" from three different plants to make up the order. We used all the 1/2" in the US, lol! Their stocks aren't huge, though obviously you don't need much. Awesome product for this application. Go with Bluewater 26 if it needs to be really stout, ie windlass mounted on it. Otherwise you can use 20 or even step back to Nautical.


Coosa Composites, LLC - Manufacture of high-density, fiberglass-reinforced polyurethane foam panels


http://www.boatoutfitters.com/coosa-...tes-board.html

[DeepFrz]

What is the compressibility of Coosa compared to hard dry plywood. I think the downfall of plywood used in structural areas is its compressibility, and then stress cracks form in the Gel Coat and water gets in and migrates. Plywood can be used effectively if a cannula of epoxy is used at every bolt point. I still would not recommend it for use on a boat.

[minaret]

Originally Posted by DeepFrz

What is the compressibility of Coosa compared to hard dry plywood. I think the downfall of plywood used in structural areas is its compressibility, and then stress cracks form in the Gel Coat and water gets in and migrates. Plywood can be used effectively if a cannula of epoxy is used at every bolt point. I still would not recommend it for use on a boat.

Never gotten specific numbers for Coosa, they want you to ask. From working with it I can tell you, it's really strong. I use it for all sorts of stuff, from deck core to bulkheads to things like autopilot ram mounts. Easily as strong as high quality marine ply like Bruynzeel, and 30% lighter. Probably stiffer too. Takes glass really well with no prep. Easier than ply to fit well, since it sands easily compared to wood. No rot, no termites, etc. etc. Only con is price, which is just a bit more than marine ply. I'm talking about Bluewater 26 here, which is their high end product. The lighter stuff is great for various purposes too.

[Neo]

Almost finished removing wet and/or rotted core from beneath anchor cleats and bow pulpit stanchions. Got almost all of it. There are a few edges of plywood that are a little wet but solid. I will try to dry out with heat lamp. They are too close to the toe rail to cut out.



You can see starboard side wet spot near the toe rail, and you can see by the shading where there was plywood and were there was balsa. See port side below were I extended the cut along the toe rail past the plywood.




Big concern is nearby toe rail, is it bedded in solid GRP or in core? In other words, is this a fools errand?
Digging out wet core (don't want to cut too close to toe rail). Paper clip hits very solid material. Horray!




Closer look, is it plywood? But why not rotted lying next to rotted balsa and very near the rotted plywood that was under the cleat? Did they use epoxy coated plywood all along the toe rail, the full length of the boat?

Does anyone have experience re-bedding toe rails in a Pearson circa 1987? Did they use epoxy coated plywood?

[sailvayu]

No I would say they did not use epoxy. Builders do not mix epoxy with polyester with epoxy and most certainly not at that period. Most builders would have "hot coated" the wood (both plywood and balsa) with polyester resin prior to installing. Why not go back with plywood? It lasted more that 20 years the first go and if you seal the bolt holes as should have been done it will last another 30-40. Do not coat whatever you use with epoxy and then put polyester over that, you will have adhesion problems. If you are just going to fill with resin and filler why not polyester resin instead. It is more compatable all around and will be just as good.