Jamie Mantzel's Fiberglass Pontoon/Catamaran Fiberglass Boat Design

obviously, you can break at all the chines, butt seams are impractical, so the boat's length is in one panel if you want it to look good

 

Did you ever entertain the idea of something like duflex pre-fab panels, fallguy ? Those Z joints look tricky.

 

Duflex-are those panels preglassed?

might have been worth the shipping costs, but not sure we'd have gotten a z press here in the states; that thing is on a trailer; still I could have made a ton of mdf clamps and if those are preglassed that would have been life changing

Click on the atl banner for the video. I didn't see the z joint profile.

Joining - Duflex - Boat Construction | Lightweight Building Panels | Architectural Panels https://www.duflex.com.au/services/joining-the-panels/

I don't get how you z joint and not glass or is the z joint relieved for taping?

 

I've never used duflex, but they are pre-glassed, infused epoxy sandwich panels. There may be provision for taped joins in some situations, but so far as I know, it is just the pre-machined edges epoxied together using the press.

 

You need to keep in mind his boat is specific for his needs. He only does short runs of a few miles between his islands and mainland, and he can pick his weather. All the compromises he had to make work for him because of that.

If you want to build in "tortured FRP" there are better ways to do it, that don't involve a mold, like Kelsall's KSS. If you do go to the trouble of making a mold it's simpler to use other sheet goods for it that can give you a better finish.
While solid FRP has been used in cats you must keep in mind that it is not a lightweight option. That's why most FRP cats end up cored, at least above the waterline.
Lastly, as the others have already said, good design and bad design need the same amount of materials and time so you better choose a good one.