Re: stringer only 1/2 piece of plywood?
It's up to you.
There is no such thing as a "most do it this way" design with this class of boats (the class most of us work on here, small boats under 40 feet). Pretty much manufacturers do what is cheapest and meets the minimum specs for the boat.
It's almost always safe to replace what the factory put in for structure, so you can do that. Within limits, extra strength doesn't hurt though, so feel free to use the double width stringer construction. It also helps when you have to put in more than an 8 foot section, since you need to overlap boards to do that.
As a compromise, you could double up thinner sheets of plywood to save weight, and it'd still be stronger than the original. Instead of two half inch pieces go with two 3/8 pieces...
Erik
