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Plywood vs Grp


bene_sails

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for 4mm ply bulkheads in a sailing dinghy i was looking at substituting 4mm 80kg/m foam and a 400g EDB both sides?

 

is this going to be roughly less/more/the same strength/stiffness/load bearing?

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It's not quite as strong bene, but I can't say by how much. Except the difference really is in how easy it is to break the ply against the foam. You only obtain that much additional strength. The real strength is in the cloth you select. Overall strength is close to the same, but resistance to being punctured is not as good with foam. It does allow you to use a cloth like kevlar or even Carbon if you want to get really carried away. And carbon is not as expensive as it used to be, so maybe worth a look at if you aren't too budget restricted.

However, there are some very very lightweight plys available also. I can't remember the name right now, but a friend has been using some ply that is light as a feather, yet still quite stiff.

 

FNG would be able to give you some very specific detail info I am sure. So if he doesn't see this and reply, send him a PM.

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is there any comparative resource on the internet that would compare the relative strengths/weaknesses of ply vs foam+e-glass vs foam+carbon?

had a quick look but couldnt see anything like it?

 

or would anyone on here know the equivalent stiffness and strength in compression of 4 and 6mm marine ply in foam+e-glass and/or foam+carbon?

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Sorry but there is some bad advice.

A 4mm ply bulkhead will not be as strong as the 4mm foam with 400gm of EDB on it.

 

Your plan sounds quite fine.

400gm of laminate on foam gives pretty good bash and bump resistance and is ideal for most applications

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i was talking ply only and i assume so was mr wolf. if you were talking ply and glass then i understand where your comments come from. cheers.

bulkheads wouldnt really get punctured in an enclosed dinghy... (heres hoping)

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Arrr, sorry I miss understood. Yes I was thinking Glass over ply and the ply nothing more than a filler. Yes, Mr Wolf is quite correct. 4mm Ply is not strong at all. If you are considering this as one single 4mm sheet, then leaving the impact strength out of the picture, I doubt the ply would be rigid enough to offer practicle structural support.

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Guest Dry Reach
is there any comparative resource on the internet that would compare the relative strengths/weaknesses of ply vs foam+e-glass vs foam+carbon?

had a quick look but couldnt see anything like it?

 

or would anyone on here know the equivalent stiffness and strength in compression of 4 and 6mm marine ply in foam+e-glass and/or foam+carbon?

 

What weight cloth? and what resin? vinylester, polyester, Epoxy?

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I doubt the ply would be rigid enough to offer practicle structural support.

 

My 3.7 has 4mm ply on the bottom and the bulkheads. The bulkheads have big lightening holes in them. I wouldn't say this stuff isn't rigid enough. It is probably easier to make bulkheads from aswell.... However as I'm not a boatbuilder I can't make an accurate comparison.

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yea im planning on building a 3.7. just exploring different options with the build really. what is and isnt going to work strength/weight wise... and time and money of course...

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When using such thin cores you can something save weight by using a higher density core. The lower the core density, the more resin required to file all of the exposed cells on the surface. Mihgt be worth having a look at 100kg/m3 or even 130kg/m3. I can't give you any exact numbers to back this up though.

 

It also helps with the impact on the panels

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