XPS Foam Core Deck

Hello,
I'm sure it's been discussed on this forum before (searched and couldn't find what I was looking for) but has anyone used XPS foam sheets as a core for boat deck with glass on each side? I'll be using epoxy resin which I don't think will melt the foam. I'm trying to save weight without paying for coosa or the like. The boat is not a work boat but will be fished often. I'm aware of using a different material for deck fittings to avoid crushing.

 

No one?

 

Don't use it, any breach in it that gets in contact with fuel, ta-ta to the foam. It's a false economy, even if it stands up (doubtful) to mechanical stresses. The money you spend on epoxy would be little different to a decent foam with polyester.

 

There was a thread here somewhere about XPS for use with things like tables or furniture. If you have thin plywood or veneer for impact resistance it can work for that.

XPS is used in SIP panels to build houses but that is properly engineered around thick OSB panels. I think 1/2" or 1.5cm or something.
The compression strength of XPS is fine if you add other material to provide impact resistance and sheer strength - which XPS doesn't have.
If you only put fiberglass on XPS you end up with much thicker laminate that you really need compared to PVC or other structural foam. Truck boxes are made like this I think.

Personally I think (and I'm still a total newbie) it only makes sense if you need thick insulation. Otherwise just use structural foam. But if you really need something like 3" insulation, then structural foam price becomes just insane. There is also XPS foam with new foaming agents that provide better insulation than structural foam with CO2.
You could build a deck with thin plywood and fiberglass on both sides of the XPS and add some thin wood ribs to increase beam strength. But that gets complicated and only really makes sense for insulation.

Then there is 3D core which is a curious case. They started with offering PET foam in hexagonal shapes for vacuum infusion which has some advantages like not needing a flow medium and creating a structure similar to honeycomb core but the epoxy resin becomes a structural element.
Recently they added slightly higher density XPS 3D core foam (45kg/m² instead of the usual 28 to 35) but you'd need to be carefully consider and probably test the mechanical properties. But it's not actually cheaper than other forms of foam. I'd love to know more about that too.

My guess is you are trying to save money? Best to include what you are trying to do and why you're trying to do it.

There is Chinese PVC foam that is cheaper than the usual stuff, would love to hear how well it works. But depends where you are and if you can import and have it shipped cheaply enough.

 

I'm always trying to save money, but I'm trying to save weight and get the most bang for my buck. As I said, its a boat deck. A downeast style boat. Boat is 32 x 9'. Not used commercially but fished often with many people and used for pleasure. What would be a good coring material instead? Coosa? Nida core?

 

There is a good post groper made on another forum. As I understand it comes down to PVC foam or balsa as the standard options since both already provide enough shear strength for a small boat. The rest is about price, if you have a flat deck and can use pre-made boards to save time, or if you want to insure against rot in case of negligence or toss ups (no balsa). The most lightweight is probably nida core honeycomb but not by that much.

I don't have the experience to make recommendations for your project, but I think it would help if you state your requirements clearer. All the options are "good" depending on the requirements

Is this a restoration, are you working from plans or designing the boat yourself?