Hi Barbara. There was a couple of college kids who built a small sub from a
propane tank a few years ago. It was called the "Manatee". It was small enough
to pull around on a cart, and could possibly be built by a young boy with
minimal mechanical knowledge. They made several dives and it worked. They kept
it very small and simple, using pedals to make it go, and a few innovative
methods to control pitch and depth. I think this link will get you there.
Although we ( old men ) often get pretty serious about our sport, I like the
idea of a boy's story that could inspire some young ones to learn more and join
the adventure. The problem is, much like scuba diving, this sport can kill you
if you make a mistake, so many of the answers you've received so far may sound a
little negative.
My daughter is a teacher and her students show a lot of interest in my
little sub project. I hope it inspires one of them to study engineering and
maybe some day have a dream of their own to follow.
Try this link and see if it helps.
My sub project can be seen on the psub site, or here's a direct link to
some photos. I hope to launch this year.
Best of luck on your writing project. Frank.