Re: Commercially available sub plans?

[Ben Trumble <trumble@well.com>]

>The first is at "www.popularlink.com/main84.html".  They call it the
>"Powersub", by description It closely matches one I saw in either PM or MI
>20-25 years back.  The one I read about was based on an aircrast external
>fuel tank and looked much nicer than the illistration in this link.  It is a
>semi-dry sub, the original had a position outside for a second diver, I'll
>try to find out which magazine/issue.

I haven't actually looked at the drawing for the powersub, but I think it's
essentially the same Popular Mechanics circa 1974 design that I used for
the semi-dry sub I put together 12 years ago -- fiber matting, and epoxy
resin over plywood, with an acrylic "dome" -- though I used a large plexi
aquarium. The problem with those plans, if indeed they're of the same ilk,
is that they don't address maintaining a more or less constant degree of
bouyancy -- and thus a stable bubble size; and at least in the sub that I
built, I had to use the second stage of my regulator -- so I was tethered
to a mouthpiece, and there was no way to vent CO2.  There is no arguing
with the fact that the no decompression rules place serious limits on any
semi-dry boat.  But then again, if you're a diver, the big plus to semi-dry
designs is that even when everything goes wrong you'll probably be okay
clutching a pony tank and sucking on a cheap alternative air rig on the
swim up.  Building a semi-dry hull, and pushing it through the water with a
Minn Kota motor is within almost anyone's budget and ability.  So it comes
around again to how to do that *better*?  If commercial plans aren't
readily available that deal with determining necessary ballast based on
hull shape and dimensions, maintaining stable bouyancy and a constant
bubble size, venting CO2, and providing the cockpit with a metered flow of
air without requiring a regulator between the teeth -- why not?  It all
seems pretty feasible at a modest price...and it would be nice to have
something to play around with while waiting on that expensive pressure hull.

Ben



"I never met a rattlesnake I didn't like."