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.

[Ad Hoc]

put a match to it...see what happens...

[KnottyBuoyz]

Take a sample strip and boil it for an hour.... see what happens...

[kach22i]

Do you need all this bridging and plywood to serve as blocking for wall mounting equipment (first aid, radio etc...) and for openings (window and door)?

If not, then you may just be able to use conventional composite construction which has no internal framing or wood skin.

[erik818]

I've tried the type sandwich you propose, with 4 mm ply / polystyrene foam / 4 mm ply and polyuretan glue. It worked fine with small area samples, but I had problems applying pressure when gluing when I did it on a larger scale. This type of construction is not new, it's used e.g. in the superstructure on caravans. I don't see why it couldn't be used on a boat superstructure if you can solve the problem of applying pressure over the whole surface when gluing. My limited experience with polyester on plywood is that it will delaminate, which is why I keep the experience limited to two attempts. I would use epoxi instead.
Erik

[PAR]

Liquid Nails will not work as your bonding agent. The "boat builder" working with you is a polyester laminator, not a boat builder and his wisdom should be followed up with sound, well tested results. In other words, he's talking out his butt, which has to make you wonder about his other "opinions".

Liquid Nails doesn't have the modulus of elasticity to work in you application. It's great for tacking down a sub floor in your bathroom remodel, but not loaded as you anticipate on a boat.

You're making more work for yourself, with this panel. You have two ways to go, stick built or stressed skin, so pick one or the other, don't mix them.

Stick built is traditional methods, frames, stringers, nailers, etc. with a skin mechanically attached. Stressed skin in your application is sandwich construction. This is a completely different engineering approach. The skins are separated by a core that can accept compression loads. A tenacious bond between the skins and the core results in a rigid panel, assuming the physical properties are all about the same in the areas you need them. In fact, your 1" bridging is weakening the whole shooting match, just with their presence.

Your "composite" panels can be made with closed cell foam, 1/4" ply and epoxy. It would also be wise to add a fabric sheathing (set in epoxy) to seal, waterproof and offer abrasion resistance. Swap out or add to this combination and you'll need to run some numbers and do some testing to insure you really saving anything. In short, engineering composite structures isn't for those that don't understand the physical properties and limitations of the materials, incorporated into the panel.