Foam Sandwich Construction

   I need a bit of advice on building in foam sandwich please, I'm currently redecking the Moth, I've used 6mm foam with two layers of 300gsm glass on either side but after the last layer on top had dried, there is still some flex in the material.
I've got four bulheads set roughly 50cm apart and obviously the boat itself is quite narrow, but in the middle of the unsupported bits I find I can press in about 1mm if I press fairly hard with the heel of my hand. 
This doesn't bode well for when I start jumping about on it, so I am now trying to decide whether to put one or more extra layers of glass on or dig a bit deeper into the funds and put a layer of carbon on, does anyone have any thoughts on which would be best?

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Jamie600 Send Private Message Find Member's Posts Really should get out more Joined: 14 Jun 05 Online Status: Offline Posts: 718	Post Options Post Reply Quote Jamie600 Report Post Quote Reply Topic: Foam Sandwich Construction Posted: 18 Feb 09 at 12:25pm
	I need a bit of advice on building in foam sandwich please, I'm currently redecking the Moth, I've used 6mm foam with two layers of 300gsm glass on either side but after the last layer on top had dried, there is still some flex in the material. I've got four bulheads set roughly 50cm apart and obviously the boat itself is quite narrow, but in the middle of the unsupported bits I find I can press in about 1mm if I press fairly hard with the heel of my hand. This doesn't bode well for when I start jumping about on it, so I am now trying to decide whether to put one or more extra layers of glass on or dig a bit deeper into the funds and put a layer of carbon on, does anyone have any thoughts on which would be best?
	RS600 1001

JimC Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 17 May 04 Location: United Kingdom Online Status: Offline Posts: 6662	Post Options Post Reply Quote JimC Report Post Quote Reply Posted: 18 Feb 09 at 12:45pm
	That may well be good enough: you don't - or shouldn't - jump about on a Moth like you do on a Wayfarer. But this is positively and completely a question to post on the Moth Yahoo group. The problem you've got if you do need extra strength is that the reinforcement should probably be on the underside, not the top.

olly_love Send Private Message Find Member's Posts Really should get out more Joined: 18 Jan 05 Location: United Kingdom Online Status: Offline Posts: 1145	Post Options Post Reply Quote olly_love Report Post Quote Reply Posted: 18 Feb 09 at 12:57pm
	there is always the arguement that a little flex is a good thing. if it is to stiff somthing with start to have stress cracking
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timnoyce Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 05 Aug 04 Location: Hampshire Online Status: Offline Posts: 1991	Post Options Post Reply Quote timnoyce Report Post Quote Reply Posted: 21 Feb 09 at 5:58pm
	I would have thought that 6mm foam with 600 grams of glass on it should be more than enough. What sort of glass have you used? I doubt that the rest of the boat was built that heavily. I agree with Jim though. Post the question onto the moth forum as they will be able to give you a better answer than our speculations.
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Jamie600 Send Private Message Find Member's Posts Really should get out more Joined: 14 Jun 05 Online Status: Offline Posts: 718	Post Options Post Reply Quote Jamie600 Report Post Quote Reply Posted: 23 Feb 09 at 10:15am
	It's 300gsm E-Glass, what got me worrying is that the rest of the boat is built from 6mm foam with, I'm guessing, no more glass on than that but the bottom and topsides seem stiffer than the deck. I've had reassurances from both Mike Cooke (Aardvark) and Adam May (Velociraptor designer) that it's probably OK, but Adam suggested I put a kickbar down the middle that would then act as a central spine to stiffen it up. I was thinking about a kickbar anyway as the new deck is completely flat, so that's two problems solved in one.
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Jack Sparrow Send Private Message Find Member's Posts Visit Member's Homepage Really should get out more Joined: 08 Feb 05 Location: United Kingdom Online Status: Offline Posts: 2965	Post Options Post Reply Quote Jack Sparrow Report Post Quote Reply Posted: 23 Feb 09 at 10:22am
	the only extra thing I can think of is that it may not be stuck down to the bulkheads 100%. kick bar is a good idea though.
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Jamie600 Send Private Message Find Member's Posts Really should get out more Joined: 14 Jun 05 Online Status: Offline Posts: 718	Post Options Post Reply Quote Jamie600 Report Post Quote Reply Posted: 23 Feb 09 at 11:00am
	Definately stuck down, I can feel where the bulkheads are and it's only flexing in between them. Oh well, I should be able to test it properly when it hits the water in the next few weeks!
	RS600 1001