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Bill, There are issues with concerning the rapid
descent of an ambient submersible: 1.
Many
divers can rapidly equalize on a fast descent while the ambient submersible
pilot has their hands full manipulating the sub’s controls on a fast dive
and may not be able to pinch their nose for a Valsalva maneuver.
Additionally, for those people that have had the pleasure of taking a ride in a
hyperbaric chamber, you will have noted that it seems to be more difficult to
clear your ears while in an air environment as compared to when your head is
submersed. 2.
Bounce
dives to deeper depths are an animal unto themselves. Recent experiences
in the tech diving world points out that a slower descent is more advantageous for
the subsequent decompression regime followed during ascent (note that all dives
are decompression dives as our ascent rate on supposed no-deco dives is there
to allow elimination of absorbed gases). Additionally, it has been shown
through laboratory hyperbaric experimentation that a bounce dive after a
previous dive should be avoided as the rapid pressurization and
depressurization causes a large quantity of micro-bubbles to be released and
this is very undesirable. 3.
Most
people when thinking of ambient subs only take into account the mass of the
sub, it’s equipment, and passenger(s). When moving, especially
fast, the mass of entrained water must also be considered. As a simple
example, a straight cylindrical (with flat end caps) ambient sub that is 24”
in diameter (a snug fit and difficult to get out of in an emergency) and 12
feet long (I am going to convert to metrics here because 1 m3 of
fresh water equals 1 metric ton) entrains 1.068 metric tons of water.
This is a lot of mass especially when considering the kinetic energy (KE) the
submersible possesses while moving. KE = mass x velocity2,
therefore every time we double our speed we quadruple our energy. For
this model case, a speed of 3 mph would equate to 1.92 metric tons-m2/sec2 and 6 mph equals a
KE of 7.68 metric tons-m2/sec2 This tells us: a. To get up to the high speed is also going to expend a lot of energy; b. Stopping is going to be a bitch; and c. An out of control, high-speed descent and subsequent meeting with
the bottom (or other inanimate object) will have unhealthy aspects for the
submersible and passenger(s). Two personal anecdotal experiences to
reinforce the KE issue: 1.
I was
part of the Florida Atlantic University (FAU) FAUboat
human powered submarine race team a few years back that set a world’s
record for speed in a tow tank located. As an alumnus, was able to
provide dry suits to keep the team warm and acted as a “catcher/diverter”
at the end of the tow tank to slow down/stop the high speed runs. FAUboat reached just under 4 kts and entrained
about as much water as our above model case). Since then the speed records has
almost double by a Canadian team if I remember correctly. As it passed through
the speed trap and then would put the dive planes to hard rise and the catcher
would attempt to grab an eye fitting near the bow to also push up and add drag
to slow the sub. By the end of the day your arms felt like they were
going to fall off and once in a while you missed and got hit by the sub (BIG
HURT’N!!). One catcher experienced broken ribs that went unreported
at the meet. 2.
The USS
Ray while running slowly with passive sonar, met up with an uncharted sea mount
(now named Hope this answers your questions. Respectfully, Jay K. Jeffries Hi Jay. Your post concerning possible injury from rapid decents
caused me to wonder. I know divers who make quick jump dives to 200 ft wherein they quickly sink to the bottom and stay
about 30 seconds and then immediately accend without decompressing since they did not stay long enough to build
up harmful nitrogen to make decompression necessary. They have suffered no ill effects and do this in a very
controlled and carefully timed way. How does this tie into your post wherein you warned against barotrauma from too rapidly
decending? Bill Akins. |