I would like to make a fiberglass seat from a mold I made years ago from a commercial glass seat that I liked.

Not wanting to make it any heavier than it needs to be, I would appreciate any advice on how many layers of glass, and what weights I should use. It is a 'sugar scoop' design, with back and some sides toward the rear, so it can't be too flexible. I am thinking maybe 8 layers of six ounce, but that is just a guess. I will be using epoxy.

Thanks for any advice,
Ralph Merriman

I think it depends on how the seat is supported/hung - I've seen seats that were bonded to the cockpit rim at the back which stiffens them up a lot.....
I've made a few NDK-style seats which are bonded to the hull at the sides and have an unsupported back, and as I recall I used layers of glass that 'added up' to about 35 oz (i.e. 6 x6 oz or other combinations) PLUS a layer of carbon fiber. Even with that (which sounds like quite a lot) there is some flex at the seat back..
I also found that I needed to use partial layers in the middle to get the fabric draping properly, but my mold has some 'square corners'....it's a good place to use scraps in those middle layers...IMO, and you can orient the layers and overlap to add stiffness where you want it (at the edges?).
I found that I got a better finish if I put a lighter layer or two of glass next to the mold.

It's always a tradeoff between weight and 'ruggedness'. Having a seat break could really mess up a week on the water... If you can avoid having a resin-rich layup it helps - I tried vacuum bagging but it was too much hassle for my level of skill.

You can always do some experiments to judge for yourself...NB epoxy takes a while to get to max stiffness..as you know.