This discussion needs to be considered in simplistic terms.

If you build a square section with flat front you will need a lot of
power to push it through the water.

This is why the commercial pontoons are tapered at the front in such
a way as to provide a smooth water flow and reduced resistance.

You can build a pontoon out of plywood by using a parabolic section
base and flat top.
(like a U section)

A thin ply can be bent around the bulkheads and the spaces filled with
flotation foam.

There is another thread on the rec.boats forum concerning attachment
loads for skinned structures. Simply stated you need to spead the
stresses out at attachment points or you rip out the plywood.


There are a number of old boat plans for pontoon boats. Maybe your
library has something.