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Hi Dan.
I agree, you would have to have a manual or
electrical pump to force the water out, but I think that
wouldn't take up as much room as air tanks.
However; I believe the hatches and viewports
would not absolutely HAVE to be built to
withstand pressure from both sides, because you will either be
equalized
or always have more pressure from outside than
inside assuming of course that you worked
your pump and valves correctly when accending. I do
see the possibility if say you
were at 99 ft (4atm), and the sub's interior was
pressurized at 2atm (33ft), and then you accended using
only your dive planes WITHOUT remembering to pump
the water out and thereby decrease the interior
pressure, that would cause a situation where
once you went ABOVE 2 atm (33ft) you would have
MORE pressure inside than outside and as you
mentioned, and that would cause overpressure in the
boat that could blow a viewport and cause a violent
opening of the hatch if you tried to pop it on the surface,
or even jam the hatch release because there was too much inside pressure against the hatch
latch. Another thing
that could happen if
you forgot to pump down before accending is you could get a leak thru your hatch
from the pressure
forcing outward instead of inward which helps to
seal most hatches. You would always have to remember
to pump your air down before accending. But I think
the benefits might be worth it since your
body could take the pressure longer and deeper in
your hybrid sub than it could in a normal ambient sub.
You just COULDN'T forget to pump the air down. One
should have a pressure gauge inside the sub and
monitor it. The only other alternative would be as
you said to make the viewports and hatch withstand pressure from
both sides, but you would still have the hatch
being too pressurized from the inside if you forgot to pump
down even if your viewports and hatch were
reinforced on both sides for pressure. You would definately have to be
sharp
and pay attention to what you were doing on
accending.
Your points are well taken and valid. I
appreciate you pointing them
out.
I might mention that Horace Hunley was killed on
one of the Hunley's training missions because he forgot to close the
water intake valves. This happened because the
Hunley could only fill her tanks about half full at the surface
because once she did
that, her interior became ambient and
equalized and would not let any more water into the ballast tanks. Her hatches
would
still be above the surface with her tanks
filled as much as they COULD BE at the surface. When the Hunley filled her
ballast tanks at
the surface as much as they COULD, there was
only a difference of 12 inches between her waterline then, verses her
waterline
before they started filling the tanks at the
surface. Then Horace had to force the Hunley
under using her forward motion and dive
planes so the superior water pressure would fill the tanks the rest
of the way.
The problem was, obviously Horace opened the inlet
valves on the surface so the Hunley could take on as much water as
she could before she became ambiently equalized and
no more water would enter the ballast tanks, then Horace forced the
Hunley
under using forward motion and dive planes. As the
Hunley decended the superior water pressure caused the ballast tanks to
start
filling again and Horace forgot to turn the valves
off, overfilling the tanks and sinking her. He got distracted possibly and
didn't stay sharp.
I can see that happening because they had to first
fill the tanks as much as they could at the surface, then the crew would crank
the
prop shaft and start out building forward motion to
force her under using the dive planes. There may have been a few minutes between
when Horace opened the tank valves on
the surface and when they actually began to
submerge.
A deadly mistake with those open top/open to the hull interior ballast tanks and no safety
backup.
A new hybrid should be built to preclude that mistake ever happening again. One way would be
to not have the tank tops open to the
hull and just use a valve instead. Possibly a valve that would automatically shut off when sensing
a certain air pressure in the boat.
You might also install a valve on the the sub that
would sense the difference in air pressure within the boat and without, that
would
automatically open to release air from the hull if
you accended using only your dive planes so the hull would never over pressurize
more
than the outside water pressure.
That would certainly make a good safety backup if
you forgot to pump the interior air pressure down.
I don't view this type of hybrid sub operation as
any more dangerous than reviewing a checklist on an aircraft before taking off
and landing.
If the pilot doesn't put the flaps and gear down
for landing it could be disasterous, same with the sub.
Bill.
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