Multi-layered hull: plywood/fiberglass

[Pauls]

Without some info on the size and type of construction it is not possible to give a good reply. Length of the boat? Hard chine or rounded?

As a generality, putting glass between the ply layers is not efficient design. The glass provides a harder layer which is most efficient in tension. On a hull with no or very little internal framing glass inside the hull can stiffen it and increase strength significantly. This is used in the Lindsay Lord construction technique.

With the normal internal framing you'd be best off putting more glass on the outside, where it will create a hard outer surface.

You can't just pick a construction technique you think is good and then apply it to a design done with some other technique. That is really a bad idea. If you are going to be doing a custom design from scratch then I'd recommend you pick up a copy of Gerr's Boat Strength which goes into detail on a variety of construction techniques in detail.

You don't say whether you are building a mono or multi. That makes quite a difference.

If a mono, genuine bullet proofing is best accomplished in metal. Yes, you can make a hell for strong boat from any material, metal just lends itself well to this.

[valhalla360]

If you just want a heavy bullet proof boat go steel or maybe aluminum if you have the skill set.

You do it in fiberglass but solid overbuilt fiberglass.

Composite construction is a great way to cut weight and for normal usage can be fine but if you plan to run it up on reefs and icebergs regularly, it's not the best option...of course most people worried about running into reefs and icebergs are over thinking things and will never go to these extreme places.

Don't just randomly modify hull dimensions and thickness. That's a great way to ruin what would otherwise be a good design.

[Smokeys Kitchen]

You might read up on some of Sam Devlin's designs. He is a longtime designer/builder in Olympia, WA and has tons of experience in building stout plywood/strip/composite boats.

I haven't looked at his site in a long time, but it's probably worth checking out or even giving a call to the shop.

https://devlinboat.com/