Hi Dean. I'm happy you are almost ready for a float test. Pretty
exciting! I haven't checked the psub site lately, got any new pics?
On the "riding the bubble" thing......I know it works, cause Vance used
it, but as an operational method of control it seems like it would add
complexity to maintaining neutral buoyancy with the need to adjust the bubble
at every depth change of just a few feet. I think Vance used that technique
when he was traveling/working at a constant depth.
The whole purpose of achieving "neutral buoyancy" is to avoid constant
adjustment of the subs weight so travel over the duration of a dive can be
accomplished without adding and dumping air at every depth change.
With a front and back tank like the K boats have you would be adjusting
for balance as well, so it's TWO bubbles you need to adjust. Could get very
busy at the valve panel when driving the sub.
It will use up a lot of air too, if several changes are made during the
dive, and when you get ready to surface at the end of the dive the ascent rate
will increase as you near the surface so releasing some of the bubble on the
way up may be needed so the sub doesn't get into an uncontrolled
ascent. It could be a delicate balancing act adding potential for
problems when coming up from a deep dive.
As I understand it, lead ballast bricks are added/subtracted to
approximate the weight needed to achieve "neutral" as payload changes, while
still at the dock. Then the VBT is used to "fine tune" the buoyancy when you
first get the sub fully submerged near the surface. Basically
"set-it-and-forget-it" so the pilot can focus on driving the sub, and use the
vertical thrusters to control depth.
I'll be diving in salt water but launching in fresh water so I'll need
enough VBT to adjust for the change in salinity, plus a little extra capacity
just for safety.
One of the ideas I really like was shown on that you-tube video. Dragging
a chain when you're near the bottom, so the sub is a little buoyant all the
time, and the chain suspended above the bottom is the extra weight needed
to maintain a given depth. You'd have to be sure the chain doesn't get hung up
on something, and have a means of releasing the chain if it got stuck between
two rocks or some how entangled, but it could make it easy to maintain a set
distance from the bottom if you were searching a large area and wanted to skim
along near the bottom while observing what's there through your down looking
window.
I've considered an anchor system where I can get the sub into position
over a given spot, set some anchors, and the sub will stay put while I work
over that spot. Like using a manipulator arm to dig a hole, or perform some
function while in a stationary position. Just settling on the bottom may be
too close to work and won't allow any movement should it become necessary. The
more options we build into our little boats, the more we can do with
them.
Frank D.