composite panels

[kelp]

Thinking of inexpensive composite panels for wheelhouse sides and back, winshield, trunk cabin sides etc. Made a test panel of closed cell 1" styrofoam board sandwitched between layers of 1/4" ply, solid 1" bridgeing every 13 0r 14", bonded with Liquid Nails compatible with foamboard, glassed on the outside. I would glass the outside with epoxy resin but the boatbuilder working with me assures me he can use inexpensive polyester resin with no concern of delamination. This panels looks to be very strong and very very inexpensive. Most materials can be had at Lowe,s or Home Depot. This is all seat of the pants, with no engineering involved but this panel is impressive,inexpensive,easy to build. Am I missing something or can I go ahead with this system. Thanks for any reply

[ancient kayaker]

The foam will increase the stiffness and provide insulation but the strength will remain whatever the two layers of ply provides. iF that's OK, sounds like a good idea, thinking of trying it myself.

[Chris Ostlind]

I have serious doubts of that described combo working effectively.

Polyester resin will melt the foam if it comes into contact with it. Since you have it buried in the core of the sandwich, there will be virtually no way to tell if the resin leaked inside while building, ruining the compressive function of the core and thus creating havoc with your build.

Epoxy is the way to go on this type of build and there's no way around the issue.

[robherc]

If the polyester resin will melt the foam (and I have no reason not to believe Chris there...just haven't tried it myself), then I would HIGHLY recommend against it, as it will be VERY hard for you to keep the polyester resin from coming into contact with the foam around the edges of the panel, where it is NOT covered by plywood...and then you might have a problem.

Just my $0.02

[Guest625101138]

Polyester will certainly dissolve polystyrene foam where it comes in contact. The foam board will just disappear. You have the choice of using epoxy with the polystyrene or using polyurethane foam and polyester. Low density polyurethane is not as rigid as polystyrene.

If you are after long life then you need to prevent sunlight getting to the wood behind the fibreglass. This would normally be coated with epoxy paint or flocoat if polyester.

You will also need to design a good joining system that gets the strength of the sandwich into the joints rather than just relying on one face board for the loads.

There are some ideas on this link:
http://www.alumashield.com/Products/...orage/CAD.aspx
I have attached an example of a roof panel to wall panel. You could use extrusions like shown or scarf the edges of the timber panel and add glass tape. Glassing would be best but you need to make test joints and try to break them. You will soon devise a suitable method.

There are ready made extrusions for normal thickness panel but yours will be odd size so I do not know what is available:
http://www.denmattaluminium.com.au/coolroom/


Rick W

[kach22i]

Originally Posted by Chris Ostlind

Polyester resin will melt the foam if it comes into contact with it.

My answer is in the duplicate thread, but I cannot believe that I missed this obvious fact.

Good catch.

[tom28571]

I use this ply/foam & beam/ply construction on decks and cabin tops. Only epoxy used in construction though. Both decks and cabin tops are crowned and can be walked on with no problems. 6mm ply on top, 3/4" foam and laminated beams on 6" centers and 4mm ply on bottom.

Strong & stiff, lightweight and great insulation.

[FAST FRED]

One delight to cored construction is you can lay up one side , turn it over , install spacers to creat a simple curve (Pilot house top, simple deck camber ) and then glass the second surface,

Works great!!

FF