Re: ambient preference

[Nathanael Henderson <jude@pconline.com>]

> the vessel when you arrive at destination.  Bottom time is certainly an
> issue ( I'm a no-deco kind of guy), but I don't see myself spending
> much time below 32 feet anyhow. 

   A few thoughts.  First, for a dry ambient sub, dive
conservatively--decompression limits and times can be affected by whether
you're submerged or dry.   Second, if you plan to stick shallow, a hooka
might be for you.   (For the unfamiliar, a hooka is an air compressor
that's usually placed on a float (such as an innertube) and feeds air
through a long hose to a diver.)   A friend of mine has a gas engine
powered one that provides about five hours of air for a single diver (more
with a larger gas tank) which may be overkill for your dive times, but
when you consider that you're going to be burning a lot of air to
equalize the inside of the sub I think it makes sense.  Cost is a few
thousand dollars.
    Regardless, I'd carry a good sized air tank with you for quick
equalization and emergency blowing of the ballast tanks, AND a small scuba
tank (pony) for emergencies.  Until the design has been tested to death,
do NOT take it outside shallow waters--you may end up on the bottom of the
lake if something goes wrong, but that's pretty surviveable at 40'.  :-)
     The trouble with dry ambient subs is air consumption.  If you have a
compartment 2'x2'x7' that's kept dry, that's going to cost you 28 cubic
feet of air to descend to 33'.  It only takes a few trips to suck a scuba
tank dry.   SO, it may be worthwhile to try to make it as shape-comforming
as possible, both to reduce the ammount of air needed to equalize it, and
to keep bouyancy changes under control (since the smaller air volume can
be equalized more quickly.
     Along the lines of safety, be sure to include a drop weight--if 'it'
happens, getting positively bouyant quick can be a life saver.  The drop
weight would ideally be enough to make you possitively bouyant even if the
compartment floods (such as by making the battery/motor assembly
jettisonable and by keeping some natural positive bouyancy in the design
(like those glue-on 'tech spheres' somebody was using.)
     By sticking to ambient pressure, you get a huge ammount of creative
and design flexibility.  For materials, fiberglass seems to be the most
popular, although I'd personally go heavily or even exclusively acrylic
(Plexi-glas.)   Mmmm, see-through sub.  :-)   THIS WILL NOT BE AN
INEXPENSIVE PROJECT.   Cheaper than a 1 ATM sub certainly, but even the
cheapest designs will probably run over a grand, and depending on how
fancy you want to get things can easily run to many times that.