plywood thickness

i have been shopping for plywood for my build, Matunuck.  i will be painting mine so the skin of the plywood doesn't have to be nice.  the place i usually use  has BS1088 Okoume and Hydrotek.  the only thing is they say it is 1/8" and 1/4".  using a calculator and seeing posts here, 1/4" = 6mm, 3/16" = 4mm, and 1/8" 3mm.  the plans call for 4mm.  would it be a bad thing to use 3mm plywood on my Matunuck?  what kind of strength difference is there?  is the real strength from the fiberglass/epoxy?  i live in SF bay area and shipping from MD is not cheap.  should i search more and find 4mm or will 3mm work fine? 

Dave


6 replies:

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RE: plywood thickness

I can't speak for the Matunuck, but I'm building my Chese 17 out of 4mm for hull and deck.  If I build my wife a shorter version, I'm going to use 3mm for the deck, and maybe the hull as well.  The fiberglass/plywood composite makes such a strong structure I don't see how it could matter, and I need to keep it light (she's 4' 11" so the weight becomes an issue for her).

Good luck,

Larry

RE: plywood thickness

Thanks Larry.  i feel the same way.  i am just beginning my search around here for the plywood. 

Another thought i had was if i can't find 4mm ply, just 3mm, would i compensate for the thinner plywood with 6oz glass? 

i am looking for thoughts and ideas.

thanks all

Dave

RE: plywood thickness

Dave - you read my mind.  The 6oz glass is a little harder to wet out (which made glassing the deck in 4oz a joy) but you could certainly make up for the thinner wood with a little extra glass weight.  On the other hand, I suppose it depends on your boat's intended use; how much stress will it take?  I've seen some pretty wild things done with those surf kayaks!  Another thought is to use the recommended glass weights but glass the entire inside, or maybe use a heavier application of glass (2 layers?) on the seams.  Just appears there's ways to compensate if you have to go 3mm.  Also, call CLC; those guys are the pro's from Dover and they'll tell you if you're pushing the limits of physics when it comes to glass/ply sandwich technology. 

For my wife (98lbs soaking wet and probably very little gear) I'd be inclinded to use 6oz hull, 4oz deck, just like the plans call for.  Someone here actually recommended the 3mm ply for the deck to ease bending it over that insane deck beam/radius.  Wish I'd have read that before finishing that step.

Keep posting,
Larry

RE: plywood thickness

Whew......  my supplier told me they had 4mm when i called them this morning.  i got there and they told me it was 1/8".  well i bought it anyway.  i got home, measured, and my 4 sheets measured 5/8".  Yes !!!  4mm plywood.  okay back to the norm.

Dave

RE: plywood thickness

Most excellent!!!  Time to start cutting!!!

Keep posting!

Larry

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