45' solar catamaran

No.

The EPS @ 18psi compression is about 18psi in shear. Terrible. Just because you had it stick doesn’t mean it will perform.

A much better way to build a cabin roof is one of a couple ways.

1. Beams laminated to desired shape. Elliptical will shed water.

2. 6mm exterior or marine plywood over the top; bed in thickened epoxy, screw in place to hold for cure.

3. Next step is up to you, but I used a combination if scrim and flat core. 12mm corecell M with shear about 150psi

4. A nice, simple 10 oz glass on top.


Caveats…

you cannot stand on eps roof, so if you want panels up there; you want it walkable

you cannot bolt or lag screw into eps

you can insulate a beamed ceiling if you use nominal dimensions for beams; mine is 1.5” plus

I broke thru the 6mm plywood kneeling on it on 11” spans before I had the core on…repaired with a patch of db1200 underneath or nothing; can’t recall

Recommendation ~ build up on beams, plywood, then pvc or san core. You can get it from Noah’s in Toronto for ? $200 a sheet. 4 sheets is 20 years no headaches 16x16, order some scrim for any excess curves, I used scrim on the outside foot each side or so, but my shape was ellipse.

My roof was about 8x14. I planned it for nominal 8’ plywood.

You need to consider snow load. I designed my roof so a 100kg man can walk on it and so snow load could transfer to the floor well. Now I am moving to Texas!! But consider the cabin walls buckling if you gutted it.

 

Sure, it's what I had in hand. Possible material is 1.8'' 30 psi EPS.
Our roof modification is not structural. It will simply be fix at the current boat structure.

Not really. There will have just enough space between roof and panels to do electrical connection and maintenance if need.
The plan is to have panel hold by there own aluminum structure who will be fix to the boat, not the roof.
Then, panels will take snow load and everything coming from sky before the roof.

Still, great input and I will clearly look at other core alternative if price are reasonable.
The thing I start to understand is cheap core can cost as much and weight more if I don't design properly. Example:
-100 ft2: EPS core only 120$, but multilayer of fiberglass + resin can go up fast ($$$$?)
-100 ft2: Gurit PVC 600$ + a simple layer of 10 oz glass on top 500$

 

Polystyrene is a terrible core material from a structural standpoint. I use XPS on occasion for odd bits and non structural uses. I swore a mighty oath to no longer use beaded EPS after cleaning up so much of it on riverways and lakes over the years.
Petg foam works well and is cost effective vrs san and pvc foam.

 

Really interesting.
But I only found PET foam core on web.
Do you have link of a supplier for this material?

 

Noahs marine has it. A caveat the first two 1/2" sheets I purchased for a stripper canoe were a homogenous white . The dozen or so later purchased, also 1/2", for a proa build were green and appeared to be made from extruded strips about 2-1/4" wide. There was no problem with the build but over time the parallel pattern of the strips printed through. This was with primarily 9 oz tooling cloth in epoxy, about half of it vacuum bagged.

There's some blend og petg and xps here
Need advice on infusion/vacuum line arrangement https://www.boatdesign.net/threads/need-advice-on-infusion-vacuum-line-arrangement.69702/#post-968500

 

China is the best place for PET & epoxy resin. Maybe 50% cost
They will ship to you.
No links, but you will find.

 

My mistake, it is pet foam, I'm swamped with last minute petg projects right now (3D printing stuff).

 

That print through was related more to epoxy cure than the product. If you post cured it; pretty unlikely to print.

I had zero printing on all post cured work and lotsa printing in non-post cures. Essentially the epoxy did not finisb shrinking…

 

I may try to do a couple of trials on some scrap this winter. I may have one more small boat project left in me and almost two full sheets of 1/2" pet with the extrusion lines.

 

I would like inputs on this one as I'm lost.
-How long my epoxy cabin parts can stay unprotect under the sun?

I mean, I plan to build cabin in 4 parts and assemble them on the boat this summer.
I will probably need many days or weeks simply to finish assembly the cabin properly and then, I will be able to put something on it (primer?).
Is this a problem?
What is the right procedure for this kind of job?

 

If I had some assemblies made that were sitting outside I''d cover them with some cheap silver polytarp and let the sun do some postcure. Don't apply any primer or other coating until all the glassing is done.

 

Make sense. Thanks for the tips.
This will also protect from rain during assembly, so it's a must.

 

Just to add.. Make sure all assemblies are ventilated under tarps. I had one enclosed assembly I did not vent and had to repair it as it ballooned under summer sun. Regardless of tarping, epoxy can chalk over if sitting out in uv. This chalk over is not good for adhesion, so all parts will require sanding before assemblies. If you are tabbing them together 40-60 grit is the recommendation. If you have tabbing reliefs, you can just sand the reliefs and after assembly; sand the entire part to the epoxy primer prep grit, 80-180 typical or as per paint manufacturer to remove any light chalking

 

I'm more convince than ever this morning.
I've tested cheap 20 psi EPS foam (1'' only), a single layer of fiberglass 1808 with epoxy each side on this 4'x3' area and it's surprisingly stiff.

So, my plan to build the new cabin roof from cheap 30 psi EPS foam (1,8'') seem totally doable.
I'm still not sure about laying one or two layer of 1808 fiberglass on this roof. Sure two layers will be WAY more strong and rigid, but it will also be two time heavier and this is challenging on our Cat.

 

The roof cannot be flat and must shed water. There is no reason to use two layers on the top. For a solar cat; you need to be able to mount the panels, so not sure how you plan to do that with 2” foam.