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    Posted: 18 Oct 13 at 1:08pm
Hi,
I have been told that using a 120kg foam rather than 80kg results in less bruising and that it soaks up less resin so that the overall weight of the sanwich panel is about the same. Is that right? I'd have thought it was the skins that mostly prevent bruising?
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alstorer View Drop Down
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 13 at 1:37pm
weight? You surely mean density...
 
bruising will be a combination of the two. A heavy skin on a light foam will be resistant, a light skin on a heavy foam may also be resistant.
 
as for resin soaking into foam, that's very, very dependent upon the chemistry and structure of the particular foam, the chemistry of the resin and the processing of the system.
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Posts: 6660 		Post Options Post Options   Quote JimC Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 13 at 2:00pm
It depends on the build quality and everything else, but given decent technique I'd be rather surprised if a layp with an 80kgm3 core worked out the same weight as a 120kgm3 one... AIUI conventionally one fills the exposed bubbles on the surface of the foam with a lightweight filler rather than leave them to be filled with expensive and heavy epoxy.

Core density certainly has a big impact on how readily the hull dents.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 13 at 2:46pm
Thanks for that, that's good to know.

It would be resin infused epoxy on a normal foam.

Looking for that elusive mix of affordable, light weight and robust - with the emphasis on maximising robustness for a set moderate weight (think Laser built to 45-50kg).
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Posts: 2788 		Post Options Post Options   Quote Medway Maniac Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 13 at 3:03pm
Originally posted by Peaky

(think Laser built to 45-50kg).

That should be easy to attain, given that V3k's come out at 54kg and yet are more than robust enough.  Mine 2006 example is still pretty much unmarked, whereas my '90's-vintage Winder Fireball had about 20 tape-covered,  impact-induced splits in the outer-layup after four years - none serious, but just caused by e.g. trapeze buckles, errant spi pole.
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Post Options Post Options   Quote Guests Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 13 at 6:49pm
I'm sure it is, I just want to make sure I have the most robust, beach friendly construction I can get for the weight.
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Posts: 2899 		Post Options Post Options   Quote alstorer Quote  Post ReplyReply Direct Link To This Post Posted: 18 Oct 13 at 8:24pm
Originally posted by JimC

AIUI conventionally one fills the exposed bubbles on the surface of the foam with a lightweight filler rather than leave them to be filled with expensive and heavy epoxy.
Maybe on (small?) boats, but with wind turbines certainly they layup straight onto core, whether infusion or prepreg
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Posts: 997 		Post Options Post Options   Quote Daniel Holman Quote  Post ReplyReply Direct Link To This Post Posted: 21 Oct 13 at 11:26pm
Weight on the bondline is insignificant on a turbine blade with god knows how many layers of thick laminate, whereas on light dinghy laminates the core bond can be 20% of the panel weight if you do it well abs best case - i.e probs double that if you don't screed the foam with filled epoxy to prevent it being neat epoxy.
peaky - not many dinghies I know use anything but 80 0r 75kg foam - easier to stock one density and double up cloth for robustness
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