It's dependent on the intended use of the boat, some on the boat lines, some on the materials, and a whole lot on the opinion of the designer.

That said, in no particular order;

1, a bent panel of plywood is much stronger then a flat panel. Curl a piece of paper and notice the change in strength. That's why arches are common on bridges and such. A bent panel does not need the addition rigidity of glass laminates as much.

2, a tube is stronger then a trough. Take a toilet paper tube and squeeze and twist it a bit. Now slit it and repeat. The more a kayak is designed like a canoe with a deck stuck on top, the more it needs the support from the glass laminates.

3, the more plywood panels there are, the more support it needs. A stripper is in a manner of speaking, a s&g with lots of tiny panels. Because they don't support each other well, it needs glass on both sides usually. It's a house built of cards essentially. same with a S&G built that way. As in multi chined, multi pieced deck.

4, bulkheads count. A real bulkhead does a whole lot for supporting the boat shape and giving it strength. If a design doesn't use them, it's going to need more glass support.

5, longer is weaker. The longer the boat is, the more prone to flexing and stress damage it will be. The panels aren't as curved (strong) and have a longer leverage arm. Hence, a need for additional support.

Lastly, use your own judgement. If the hull seems weak to you, and you know you're going to use it hard, reinforce accordingly. The worse you're going to do is overbuild it and make it heavier then it need be. If that's acceptable to you, then there is no problem. I'd have a lot more caution about going the otherway, in skipping reinforcement the designer advises.

> In reading the matierial from several S & G kit manufacturers
> I noticed that they take different approaches to glassing. One provides
> for FG on outside & inside of the hull + FG on outside of deck.
> Others FG outside of hull only, tape inside seams & no FG on deck.
> Is the inside/outside hull FG & deck FG really necessary?