Epoxy over XPS method

Hi RX - can you give an idea of what an approximate cost to rent a boat building shed sufficient to build a 15-20m cat in Cebu should be? I did not get a response to the email i sent about this for a suitable shed that was advertised on the net...

 

Do you just want a shed with utilities and you are going to supervise, hire locals, bring your own tools? There are plenty of small shops there that build fiberglass boats. I can ask around.

 

Yes was planning to hire locals to help speed up the build, get together a small team and supervise the construction... doesnt have to be a flash place, just big enough to fit a 15-20m catamaran with access to water, skilled labour and materials etc... An overhead gantry crane would be nice - tho not really essential. Just looking for estimates on costs as ive never been to the Philippines and do not know what the going rates are for these things...

 

If you do want to insulate your hull though, would you try to use XPS to add stiffness? Say something like 2" XPS foam. I realize most boats don't insulate. But theoretically it's a use case where you'd want to use XPS on the hull.

Hull with structural foam sandwich + XPS insulation + laminate for interior.

The boat plans would need to be engineered with an FEA simulation and careful design to "protect" the xps. But you would want to make use of the added stiffness and try to save some weight. And cost. Not save 90% on expensive core foam but maybe 40%.

I wonder if you could one shot vacuum infuse a complex sandwich panel like that in a mold? Probably would need to add bleeder channels to the XPS foam. Adding insulation afterwards also would seem like a huge hassle, if you can do it in the mold instead.

Maybe an airtight hull and the PVC foam insulate "enough" so this is just not worth the hassle. XPS insulates better, but the spaces are so small that heating or cooling is easy. How many boats do add insulation foam to the hull? How many just insulate a small portion of the cabin?

 

In theory it could be done with careful design and appropriate engineering, im sure it could work.
In practice i think you find better ways to insulate a boat. Most seem to be going with that spray on insulation which expands and then sets within minutes of spraying- not sure what its called. They use it in homes too.
The problem with a complex sandwich core is both time and money. What you save in $$$ with xps you a partially loose in the extra glue lines to hold it all togeather- could have just used higher density foam all the way - same goes for the weight, and all the way you adding more time with the conplexity. Time is a big enemy in building...

 

PU spray foam. But I read it's friable with vibration. And it creates a lumpy surface.

 

I doubt the friabilty is a problem- that stuff was tenacious as all hell from what i saw... yes it leaves a lunpy surface but its very easy to trim back any areas that end up proud- and then you use an interior liner to hide it all. Or a seond molding for the inside finish surfaces which drops in over the top to cover it all...

 

Yeah ok, that would definitely be faster!

 

In theory it could be possible to incorporate xps into a hull core for a boat that wasnt too large- what i doubt is that there isnt a cheaper or faster way to acheive insulation properties...

 

I'm thinking of a rather rectangular hull like this as an example, where it should be easier to infuse it. But I just looked up the thermal conductivity of corecell and it's 0.03 to 0.04 W/(m·K) which is the same as normal XPS with CO2, while the XPS with the newer blowing agent achieves 0.027 W/(m·K). So even in the rare case where you would need more insulation, you are right, just using thicker structural foam saves you time and money.

 

A dozen or so years ago, I was on the build team for a one off 40 foot racing sloop. Well into the build several race organising authorities announced the need for greater post catastrophe buoyancy than the then requirements. To meet the next generation requirements to go into effect in 5 years, we bonded XPS to the inside of the structurally completed hull.

 

Weird. Just after this thread I found that there is a new XPS foam for vacuum infusion. I've seen this hexagonal 3D-core PET foam before which sounds pretty smart because it's easily conformed to curves and creates a hex-pattern made out of resin inside the foam with vacuum infusion, but now after they had PET on the market, they now came out with a high density XPS foam.

You can see the claimed properties (table in english, see "HX") for XPS foam (45kg/m³) aren't bad compared to the PET foam (80kg/m³). This is from a seller, the manufacturers website has less info. XPS is lower density but somehow also less resin uptake (more precise cuts?). I think normal XPS is 30kg/m³ and XPS for floors is 38kg/m³. They also offer it with triangles and rombuses.

But it's not cheaper than the PET, just lighter and less resin uptake. If it's not meant for structural applications, what is is meant for? Maybe the XPS stuff could be useful for making a plug with compound curvature.

Has there been some discussion about this 3D core foam (PET) already? Anyone tested it? "3D" and "core" is hard to search for. Mostly interested in the PET. They are also announcing they are making a PMI 3D core. And this isn't more expensive either. Is the resin uptake worth it? Do the thin epoxy walls between hexagons added significant strength? How does this resin update compare to PVC foam that is scribed or punctured?

 

I am enjoying this thread. Without any further input from the OP, it has taken on a life of its own.

 

I guess that's why they are called threads? If you keep pulling it unravels

 

Dejay: Finally someone mentioning the fact that XPS comes in all kinds of grades. The densest XPS marketed for construction I can find is 45kg/m3, and has a compressive strength of 700mpa; seem to be the same stuff as mentioned in your table. Those properties are in the same ballpark as low/medium density foams marketed for boat building, as your table also agrees. But looking at prices, the construction grade material is still about 10x cheaper than the best deals on boat-grade foam i can find; probably just because it isnt targeting a niche market, but sold by the truckload.

What the demands on the foam are is a subtle question that requires quite some quantitative understanding of the underlying mechanics, and is quite dependent on the precise area of application and its anticipated loads. So I am not saying high density XPS is the answer to everything; but going by the numbers is sure seems like a cost effective solution for the areas that are not demanding the most from the core.