Hi Brian. (" tapping on the side" ) That's definitely low
tech, but not quite as accurate as I'd like. I think that with a little
practice, a guy should be able to approximate what level is needed to achieve
neutral buoyancy. That level can then be repeated as long as other factors
affecting buoyancy remain constant. However, changes in temperature, salinity,
and depth ( it's much colder at depth around here ) can require small
adjustments that only a VBT can provide. If I start out at a river mouth
launch site where there's very little salt in the water, and then motor out to
the ocean, the difference in buoyancy, although not that large, would make
adjustments necessary. This scenario is typical of where I plan to dive. Both
of the local harbors near here are situated on rivers. With a displacement of
900 gallons, the difference in salinity/water density will make a difference.
I'll need some way to set the level in the tank about half way full, and then
repeat that level consistently on following dives with out time/energy
consuming re-balancing the boat to neutral.
I'll be carrying lead bricks on the inside for major weight changes like
a passenger or additional equipment for a specific dive, and the drop weight
is adjustable also with a little wrenching, but being able to repeat a level
of buoyancy consistently when all other factors remain constant should make
multiple dives easier and faster. I want to maximize the useful time spent
submerged without spending too much time adjusting for neutral. Did you see
the composite propane tank link Greg put up ? that looks promising.
I'm still not sure how big the tank needs to be. It's probably not that
critical, but the amount of fine adjustment needed is affected by several
variables. And then there's the amount of air it takes to change that level.
If you can set the level at the surface, it takes only a little air. If you
need to make adjustments at 300 ft. then it takes a lot more air, and then
you've got a pressurized cylinder inside the sub with water in it. That will
need to be dumped once you get back to the surface. Of course, I've never
actually done any of this before, so maybe I'm over thinking it. I'm certain
there's going to be some design changes needed after I get this thing wet.
Some of them will undoubtedly be expensive fixes. I just want to avoid
dangerous mistakes.
Frank D.