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Andy, Thanks
for your thoughtful reply. Expelling
a gas into the water results in the water’s density dropping due to the
entrained gas. A sub would still loose buoyancy even if the gas is
expelled in a horizontal manner and it bubbles above the sub. The sub
would be trapped at its depth until the gas stopped and the density of the
water above increased. This same effect is what causes a wreck survivor
to be “sucked” down by the sinking wreck (in actuality, the
survivor is experiencing decreased buoyancy versus being sucked down). Propulsive
power sufficient for the environment that the submersible is to operate
in. This is different than speed. There are also some high current
areas that are sufficiently strong as to be not suitable for most PSUBs to
operate in. When
I spoke of a frozen valve, I meant iced up. This will occur even with
very dry air. As
I mentioned earlier, even though a wet sub doesn’t weigh all that much,
it entrains a lot of water (greater than a ton for most streamlined human-powered
subs). This is included in the momentum of the sub. Believe me from
personal experience…you don’t want to get in the way of one of
these babies and try to stop it. More than one has hit a wall or the end
and damaged the sub. Even worse, is the sudden stop for the sub’s
occupants. You
are correct that Deep Flight’s speed is for open water operations
in diving and not for fast cruise on the bottom. They worked on Hawk’s
Deep Flight for a long time and you don’t hear much about it
operational deployment. How successful is it really? Do you have
any background on this Andy? Hawk’s pretty much used slave labor to
build it. J Jay Respectfully, Jay
K. Jeffries Andros
Is., Bahamas Talk
sense to a fool and he calls you foolish.
- Euripides (484 BC - 406 BC) -----Original Message----- I agree 100% with Jay's message and hence the "The
following should be filed under "insane" caveat. Perhaps that should be changed to "ABSOLUTELY
INSANE". I was just trying to think of alternatives to those already
discussed and crossed off the list. I can also not really imagine a scenario where high speed
at the bottom would be useful. A relatively high speed (i.e powered)
descent from the surface to near the bottom can be nice if it can be
accomplished safely and you are going deep In response to Jay (and no I am not really advocating the
use of high pressure retro-rockets...but in the interest of curiosity (which
did kill some cats): Propulsion CAPABLE of high speed can be useful to fight
currents. 1) You really care about momentum, so you can trade off
your reaction mass with the velocity you expel it. Of course at this
point you may have to up-scale from scuba bottles, which is probably WAY more
dangerous than the risk of hitting something. 2) Didnt see that mythbusters. If you have a gas
compressed in tanks to a higher density than water, you shouldn't loose any
buoyancy (DONT TRY THIS), and was thinking more about fast horizontal
delta-v near the bottom, where a loss of buoyancy is not the major concern. 3) if it was for absolute emergencies then a stuck valve
doesnt seem like a terrible price to pay. Assuming there was a redundant
system to blow ballast. Also, some shallow water wet subs can move pretty
fast. But they dont have the mass behind them that would make a collision
as dangerous. Also some of those bigger psubs may cause a pretty
big mess at low velocity collisions. So maybe "PSUB momentum kills" ? or really "Operate in the envelope" is probably
the correct message. FWIW: Deep Flight I has a max cruising speed of 12 Knots
and a Min of 2 Knots. But I think the idea is that it is super
maneuverable rather than able to break, and high speed is used primarily for
descent. Still cant imagine12 Knots at the bottom...heck 2 knots
seems fast. It does only weigh 3000 lbs... -a |