That's odd.  What kind of ply was it? Okoume should settle into place without complaint, but "lesser" plywoods such as luan and poop-quality ply box-store board can be resistant to curves and seaworthiness and such, and will want to pop apart even weeks after they are curved.

Another possibility is lack of 'wet-out'. The strongest joints are made by applying un-thickened 'pox to both peices of wood in a joint, so that the pieces soak up the epoxy. Typically, they'll need application of further unthickened 'pox until they stop soaking it it up. Once they are saturated, then (and only then) apply the thickened gap-filling mixture. That way, you avoid 'dry joint's (where all the 'pox has been absorbed by the wood, leaving none in the joint itself), and 'thin' joints (where the epoxy isn't sufficiently 'rooted' into the wood itself, so that it can just peel off the end grain like two-sided tape would...).

Finally, bad fillets could be the culprit, but I've never really seen a filet so bad that, in the absence of the other two possibilities, it would split a joint apart...

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Catherine, by "delamination" do you mean your epoxy glue joint failed between the plywood deck and the timber sheer clamps?  Or did the individual plys of the deck plywood itself separate from each other? 

How did you originally attach the deck to the hull?  With thickened epoxy and ringshank nails?  Did you overlap the deck fiberglass down the sides an inch or two, to reinforce the hull-deck joint?  A couple pictures would be helpful, if that's a possbility.

Grant

Hi Grant and David, 

Thanks for the answers. Here are mine:

- I used Okoume plywood (3 ply)

- As a matter of fact, I didn't wet the cracks with unthickened epoxy before filling it with thickened epoxy... 

- By delamination I mean that the individual plys of the plywood deck itself separate from each other.

- When I attached the deck to the hull, I applied unthickened epoxy on the entire inside deck, then I applied thickened epoxy on the sheer clamps. When I bent the deck over the hull (with many straps), the nails weren't enough to keep it in place between the straps, so I used screws. When everything was cured, I removed the straps AND the screws and filled the screw holes with thickened epoxy. Then I rounded the joint with a block plane, sanded and put 4 oz fiberglass on the deck, overlapping the sides by two inches. 

- I'll post pics as soon as I can! 

It woould seem to me that, if the plywood is delaminating, it is getting moisture into the plys.  Did you perhaps sand thru the glass at the deck edge?  If that glass is intact I cannot see how delamination could occurr.  Another questions:  Did you build from plans?  If so, I understand that the plywood is Okoume, but is it BS 1088 marine plywood? 

Also, I note that you applied unthickened epoxy to the underside of the deck.  Did you install the deck while that was still uncurred?  If it was allowed to cure, the deck would have been much stiffer and more difficult to install properly.

Keep the info flowing.  there are lots of smart folks on this site who can figure out how to solve almost anything.

Paul

Catherine,

I picked up several things from what you said.

You questioned if your bevels of the shear clamp were the wrong angle. The deck should be smooth from well before it gets to the shear clamp all the way to the edge of the boat. If there is a change in the deck, like a small ridge or bend, where it crosses the shear clamps, especially above the inside edge of the shear clamp, your bevels are too steep. This will put a lot of pressure on the wood and may cause it to delaminate.

Someone else asked how thick the wood was and you said 3 ply. 3 ply is how many layers there are in the wood. 3 ply wood comes in several thicknesses. If you used more than (probably) 4 mm plywood for the deck, it may have been too stiff and may be why it is delaminating.

If you combined the two problems it would really cause the wood to delaminate.

When I did the deck of my CH17, I only used one strap. I put it on over the deck above the front deck beam and nailed both sides (2 nails on each side at a time) from there forward. The nails pulled the deck down into place as I went along. I then did the same for the aft deck. Unless the wood was too thick or the bevels were the wrong angle you should not have had as much trouble as you reported.

Hope this helps.

Hi guys,

Concerning the wood, I bought marine Okoume plywood, 4 mm from a supplier in Ontario (I'm from Quebec). Should have opted for the 3 mm I guess...

There is no ridge or bend in the deck when it gets near the sheer clamps, and I used a guide to obtain the good angle for the bevels, so I guess this is not the problem.

I applied unthickened epoxy really quickly in the inside of the deck and then I applied the thickened one on the sheer clamps, and I glued everything together before it could cure, I swear, I was so tensed about that part of the building!

The hypothesis of moisture into the plys is the most probable from my point of view. Maybe I sanded the edges too much and went through the glass... But then I varnished my boat. Maybe varnish wasn't enough to keep water out? One thing I'm sure, is that when I noticed the delamination first, I also saw that the wood there was soaked with water. Before I made the repairs this year, I let it dry for several days.

I feel like it's a real mess honestly. Because the screws didn't look good, I painted the edges of the deck (which is really good looking now). Now I'm thinking about putting glass strips on edges, but I would have to sand everything back to wood, wouldn't I? As I already put one strip from bow to stern along the chin... My kayak is becoming a heavy tank!