Thickness of marine-grade plywood

urbanbiketech · 30 June 2009, 04:30

Hi,

I'm going to be building my two-piece floor (Futura Mk2) tomorrow. I have the choice of 3/4" (19mm) or 1/2" (12.5mm) marine-grade plywood. Can someone tell me which thickness I should choose. I would prefer to keep the weight down, but am willing to sacrifice if necessary.

Thanks,

Vince

chewy · 30 June 2009, 07:47

How thick was the original floor, was it wood or alloy?

urbanbiketech · 30 June 2009, 13:47

Hi,

I don't know. My current floor is an H2P air deck.

Vince

prairie tuber · 30 June 2009, 14:17

Half inch marine plywood might be OK, 5/8" should be plenty, 3/4" is very heavy duty. The highjackers will give additional longitudinal support compared to a conventional inflatable keel. My boat model uses 5/8" marine mahogany plywood as the standard thickness, but I opted for 3/4" marine for the extra strength and rigidity. For me the extra bit of weight was well worth it. My 3 main aft floorboards (~ 48" x 36" per board) weigh close to 50 lbs each.

Can you also get 5/8 marine plywood? Is your supplier able to tell you the weight/meter2 of these different thicknesses. From there, if you roughly calcuated the surface area of your floorboards, you can determine whether the incremental weight increases are acceptable to you.

chewy · 30 June 2009, 14:53

I'd go for the thicker stuff!

urbanbiketech · 30 June 2009, 15:31

Keep in mind that I have only a 25hp motor. I would like to keep it light but not if it means using thinner than recommended. I don't want to overkill it for the sake of it, either.

chewy · 30 June 2009, 15:43

If weights an issue can't you get some fibreglass ones made?

urbanbiketech · 30 June 2009, 15:59

Quote:

Originally Posted by chewy

If weights an issue can't you get some fibreglass ones made?

That's a pretty sweet idea actually. I'll look into it. For the time being (and I mean for my fishing trip 2 days from now), I'd like to use wood.

prairie tuber · 01 July 2009, 14:13

After having had both aluminum and marine mahogany plywood floorboards, I much prefer wood for the following reasons:

- Marine plywood is considerably less expensive.

- If using a suffficient thickness, marine plywood it is much more rigid.

- Marine plywood is very easy to modify and customize in terms of anchor points for your particular needs & deck layout.

- You can easily & quickly make additional/spare floorboards. This way, depending on what tasks you may using your boat for, you can install specific floorboards that are set up for that particular task. This is why a good sized SIB can be considerably more versatile than a RIB of similar size.

Fishery Pokery · 02 July 2009, 15:05

If you painted the floor, would you get away with exterior ply, as the floor is not submerged? And if so, what paint do you use on them?

prairie tuber · 02 July 2009, 15:17

Quote:

Originally Posted by Geoff_Jubb

If you painted the floor, would you get away with exterior ply, as the floor is not submerged? And if so, what paint do you use on them?

The paint will quickly rub off at the edges. I doubt you would get a full season out of floorboards made of conventional plywood. A given thickness of marine mahogany will also be much more rigid than conventional plywood.

m chappelow · 02 July 2009, 15:21

Quote:

Originally Posted by Geoff_Jubb

If you painted the floor, would you get away with exterior ply, as the floor is not submerged? And if so, what paint do you use on them?

i was told by a marine ply supplier a good while back that most exterior ply was now resin bonded same as marine ply ,as a mate of mine was after some to build a boat with and said if its painted it should be fine ,though as p/t just said its the hard wood stuff that will be best .suppose you could give it a coat of grp resin .

stan_deezy · 02 July 2009, 16:00

Quote:

Originally Posted by m chappelow

i was told by a marine ply supplier a good while back that most exterior ply was now resin bonded same as marine ply ,as a mate of mine was after some to build a boat with and said if its painted it should be fine ,though as p/t just said its the hard wood stuff that will be best .suppose you could give it a coat of grp resin .

Ditto!

My SIB has two different decks, one the original multi-section deck as supplied, the second one home-made from Birch ply. I looked at marine ply (£60/sheet!) but the supplier pointed me towards Birch ply for several reasons: exterior rating, 13-ply compared to 6-ply, resin bonded, used locally for boat hulls and also used by local hauliers for decking flatbed lorries without any problems. Best of all it was £29/sheet for 18mm

prairie tuber · 02 July 2009, 16:43

Thanks Stan,

The 18 mm birch plywood sounds like a good reasonably priced alternative. Let us know how it holds up.

Fishery Pokery · 02 July 2009, 17:41

Quote:

Originally Posted by stan_deezy

Ditto!

My SIB has two different decks, one the original multi-section deck as supplied, the second one home-made from Birch ply. I looked at marine ply (£60/sheet!) but the supplier pointed me towards Birch ply for several reasons: exterior rating, 13-ply compared to 6-ply, resin bonded, used locally for boat hulls and also used by local hauliers for decking flatbed lorries without any problems. Best of all it was £29/sheet for 18mm

Did you treat the ply Stan? Did you paint it?
Also, did you us a turnbuckle or did you make it but up to the thrust board?
Cheers,
Geoff

stan_deezy · 02 July 2009, 18:29

Ah yes, missed out the bit about treating the timber! Used a primer coat and then two coats of undercoat followed by two coats of International paint. Stood up to wear extremely well indeed. No turnbuckles required, butts up to the transom and the small bow board very tightly to keep the fabric taught. If the fabric shows any signs of sagging I'd seriously consider turnbuckles though.

Fishery Pokery · 02 July 2009, 20:07

My boat has 3 pieces that lock into aluminium side channels, then a triangular piece with a hole in for the keel valve, then a smaller triangle that is permanently fixed to the boat.
Do you use the single piece to replace the 3 bits that lock into side channel, or do you replace all 4 removable pieces?
Thanks,
Geoff