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I have found pvc sheets for a good price. Would pvc work for a solid core material. Glasses and bedded with epoxy.

I can get pvc boards for 45$ compared to 250$ for coosa

I dont follow what youre trying to build. Are the pvc boards 4x8ft? How thick? Wherr u finding them for 45$?

Rebuilding my cabin top on my 26D. You can search my build. Replacing the entire cabin top core. Finding the 4x8 pvc sheets locally on Marketplace. Just not sure if they would be able to be bonded together. Or if resins would stick. I’m looking to stack 3 layers of 1/4” to make the core completely solid from the cabin top liner to the top of the cabin deck.

I don’t know about compatibility of pvc foams with epoxy. Looks like McMaster sells some that is intended for composite building, so seems within the realm of possibility.

I think laying up 3 layers of 1/4” to get to 3/4” might be a pain and use a ton of extra resin. If the foam is lightweight enough, maybe it wouldn’t add that much weight over 3/4” plywood, which also isn’t light.

Have you given up on wood completely? I don’t think it has to be marine plywood. Balsa is used in boat decks all the time, and there is nothing “marine” about balsa wood. What kills deck core is water intrusion. Keep it dry and it will last indefinitely. I think the problem is builders have no incentive to bother potting all their deck holes, they just bed the hardware, which they would have to do anyway to prevent leaks. Then 15 or 20 years later, when leaks start, owners ignore them because “it’s just a small drip”, so the core is given years and years to soak up water.

On both 30+ year old boats I’ve owned, the deck core was perfect everywhere is was still dry.

I havent given up on a wood core just yet. I actually found locally some exterior meranti 1/4 sheets at 4.50$ for 3/8” thickness. I know it’s not marine but when coated with resin and all hardware potted properly I too think it will last another 30 years.

Yeah, that’s where my head would be at. Marine plywood rots too if it’s wet for long enough. I think the big advantage is the glues used are actually waterproof, vs something more like water resistant for exterior grade ply.

On the big boat I don’t own anymore, the diesel tank sat on a sheet of 3/4” marine plywood, down near the bilge. This combined with deck leaks (ties into my last comment about previous owners ignoring leaks), meant every time the boat healed to port, the plywood shelf and bottom of the tank got doused with bilge water. I ended up having to pull the tank (aluminum) because the bottom had pitted bad enough to start leaking. The marine ply, true to form, had not delaminated at all, but some areas had rotted enough that I could pick it apart by hand.

Should I be worried about the added additional weight if I add more or thicker plywood? I would think I would be adding at least an extra 100 lbs. should I be looking for something lighter? Maybe back to the pvc sheets to save weight? To many choices.

Weight at deck level is bad for stability. How bad? I guess I don’t know. I think this is one of those situations where it matters, but drawing the line is really hard.

Would the boat sail fine with a 100 lb person sitting on deck? I would assume yes. But then you have to think, every time you go on deck, now it’s you plus that imaginary small person.

I was thought-exercising a radar dome on the mast. That would be about 20 lbs, say 17ish ft up the mast, so about 20’ off the water. If the COG of the boat is at the waterline (it’s probably not, but close enough), and the ballast COG is 3’ below, adding that 20 lb dome would be equal to removing 130 lbs of from the swing keel. Considering my keel is 625 lbs, that seems like a lot (20%).

Running that same experiment on a 26D… say the COG is at the waterline, deck is 3’ above, and water ballast is 1.5’ below. 100 lbs added to the deck would be roughly the same as removing 200 lbs of water ballast from 1,200 (per sailboatdata)(17%). Does that 17% matter? I guess I have no idea.

I’m not sure either but if I can’t keep the weight at a minimum then I could offset the new cabin weight with a larger battery bank down lower

So I got myself some 1/4" pvc panel from one of the big box stores. Made a little layup with three strips and one layer of 1708 on the bottom. This would make the section 3/4" plus the 1708. There is not enough stiffness to be used as core for the cabin deck. I may try another test today and lay up three more sections and possibly add 1708 between each layer and two on top. This is over kill but I have some scraps that would work for this test. Ultimately i doubt it works and a wood core seems the best option at this point. I was really hoping to be able to have a solid composite core as an upgrade.

So I tried another layup schedule. I used 3 layers of 1/4" pvc with 1708 on the bottom, in between each layer of pvc and 2 layers on top. So in total 3 layers of pvc and 5 layers of 1708. The good news is the pvc and epoxy were bonded well. I used some scrap peel ply and vacuum bag film to keep the work station clean. When removing the peel ply there was a small section that was pulling up the glass which was tearing the pvc. So the pvc failed before the glass epoxy bond to the pvc failed. This layup was much stronger, but still bowed to much when weight applied. When the 4"x30" section length was placed on 2x4 at each end, my weight, 265lbs, was able to bend the middle to touch the floor. So the PVC is out and marine ply is ordered and hopefully will be here this week sometime.

I used this stuff...

https://www.plascore.com/

It is solid as a rock.