Hi Doug. Because my sub is made from 2:1 semi eliptical tank heads, I took
an old BBQ propane tank and used it as a mold to make fiberglass half
domes. I then made some foam shapes to approximate the front and back
structures/ballast tanks and glassed them on. Next I made some little window
rings, and a hatch using the same foam techniques. I have some small plexi disks
that fit in as windows, and will make some wings/motor mounts and drop weight
shape. Glue all the stuff onto this basic model, and I'll have a fairly accurate
model for flow testing. I made the model large enough so I can get my hand into
the opened hatch to add/change weights as I need them to adjust for neutral
buoyancy. Then I'll take it over to my buddy's house and plunk it down in his
pool. I used a weighted string to pull the old models through the water, and it
gives me a pretty good idea how the sub travels through the water at different
speeds. Frank D.