New Deck,

[Redeye]

Morning All,

I intend to rebuild the deck on my 22' primat. Currently, it is two layers of 4.5mm ply ( I think) ... maybe it is one layer of 3/8 in some places ... built in the 60s over kauri framing, and with a paint finish. The top veneer of ply has started to badly delaminate, and after making ugly emergency patches and applying epoxy etc, I've just decided to rebuild whole deck.

It'll be better in the long run and not much more expensive I think. as I need to epoxy the whole thing anyway I can also enlarge the cabin a little to the long cabin design at the same time.

I'd like to add a layer of glass in epoxy to the new deck to add to the longevity and protect the wood.

My question is if I make the deck from one layer of 6mm ply, and then glass it, How much glass should i put on there to compensate for the 3mm of lost strength from thinner ply? or is the 6mm okume (it has a layer of some reenforcing material in the middle) probably strong enough?

[boattruck]

Red, In my opinion, a two lam ply deck, well glued together with epoxy or the like is alot stronger than a single lam. Unless I am somehow increasing the strength( better materials etc), I would not reduce the existing scantlings of the boat. In your situation, I would think it would be two lams,4mm or 6mm each and a glass/dynel and epoxy coating and then paint and nonskid of choice to meet or excede what you had...Cheers, BT

[Redeye]

Thanks BT,

Yes I finally got off my lazy bones and dug out my copy of Boat Strength (Gerr). did a few calculations and yup, I'll stick with 8 to 10mm of ply and a layer of 200 gsm glass in epoxy. then some good paint.

I did wonder about using 9mm ply in a single layer with good scarf joints to avoid the half depth butt joints which I would get if I use two 4mm layers. The 9mm is like iron though and probably won't bend to take the deck camber.

Why is two thin layers better than one thick layer - other than for being able to bend it more easily.
I would have thought that the glue between the veneers of the BS1088 would be more perfect than that which I could produce between two layers of ply...

[boattruck]

Red, When you laminate the thin layers of ply, there are two or three distinct advantages;1, As you noted ], it bends easier. 2, You have the opportunity to stagger your butt joints, reducing point loads. 3, As two or more laminates are built up, you develope 'form strength' IE, the laminated ply deck is now helping the aging deckbeams do their job. Add a nice coating on the bottom to seal it up, much easier to do on saw horses, than in the boat...And a strong glass and epoxy skinon top, protected by paint, this is a strong long term deck...Cheers,BT

[Songololo]

Have you seen this thread. There is a section on p 7 showing details of how the deck was constructed using multiple layers of plywood. May give you some ideas even though it is for a larger boat.

Pics of your deck?

[Redeye]

Yeah I saw the pics of that deck being made, it certainly is strong. I'd love to put a ceiling in my boat (sorry no pics yet) and layer some ply on top, but there is a minimum thickness which is useful for each layer, so if I was to put in a nice ceiling, a couple of layers of ply, some glass, and then some teak, i'd be over 30mm I'd guess, and that'd make the deck a touch on the heavy side...
she's only 23', and the hull skin is only 12mm.