Repair & maintenance: Foam Sandwich Construction

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Foam Sandwich Construction

Printed From: Yachts and Yachting Online
Category: General
Forum Name: Repair & maintenance
Forum Discription: Questions & tips on the subject
URL: http://www.yachtsandyachting.com/forum/forum_posts.asp?TID=5178
Printed Date: 15 May 25 at 3:44pm
Software Version: Web Wiz Forums 9.665y - http://www.webwizforums.com

Topic: Foam Sandwich Construction

Posted By: Jamie600
Subject: Foam Sandwich Construction
Date 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?

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RS600 1001

Replies:

Posted By: JimC
Date 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.

Posted By: olly_love
Date 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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TWO FRANK-Hunter Impala

Posted By: timnoyce
Date 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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Cherub 2648 - Comfortably Numb

Posted By: Jamie600
Date 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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RS600 1001

Posted By: Jack Sparrow
Date 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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Posted By: Jamie600
Date 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!

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RS600 1001