[SloopJonB]

3/4" bulkheads would be excessive on a boat that size. 1/2" is plenty. Triple tabbing of 1708 biaxial would be super strong - double tabbing would be plenty good.

Don't fall into the amateurs trap of "a little stronger, a little beefier" - it's a fast way to a slow, overweight boat. You should always be looking for ways to lighten things up, not increase their weight & size.

 

[SloopJonB]

Crazy idea - not even particularly cheap. Use epoxy coated ply and do a good job of tabbing it in.

For ribs, just use foam or PVC tube or even cardboard tube as formers and laminate glass over them.

 

[SloopJonB]

Think I'd probably find some dense foam like some polyisocyanurate insulation to form the substrate. I'd just shape it and stick it to the hull inner surface with some contact cement. Then you could glass it in immediately. Don't forget to feather the adjoining glass at a 12:1 ratio. If the glass is 1/4" thick, taper back approx. 3". The first glass layer needs to be the biggest pc.

That's a very good way to go but shaping it can be labour intensive. Cutting PVC tube in 1/2 and tacking it in place with hot melt glue is quick & easy, Doesn't weigh anything really and the round shape is easy to glass over. It also holds screws when you fasten a wood ceiling over it - the glass alone is too thin to do it well and foam does nothing.

 

[SloopJonB]

If you cut the PVC in 1/2 lengthwise it gets very limber - hot melt glue will tack it in place

 

[SloopJonB]

Would you predrill for the fasteners?

ABS is easier to get in our region, do you see a problem using that?

I'm assuming I should use 1" Schedule 40 cut in half?

Thanks

I wouldn't pre drill. You can use anything that wont get melted by the resin. I've seen cardboard mailing tube used as a former. The advantage to using 1/2 a plastic tube is that screws can get a bite in it when you put a ceiling in - no other reason.