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Hi Brian. That's how it COULD work. I don't think that's how best to use it
though.
As I understand the variable ballast tank ( VBT ) it's used as a fine
adjustment for buoyancy. Changes in buoyancy occur on several occasions. The
salinity of the water, like if you go from a fresh water harbor to salt water,
or even pass through a salty layer in the ocean, or a fresh water current in the
ocean near a river mouth. These things will have an effect on how buoyant a sub
is.
Water temperature can make a difference too. Although not much, it gets a
little more dense when the temp goes down.
I think the most common way to handle the VBT is to adjust the volume of
water in the tank while submerged at a shallow depth, to achieve neutral in the
water column. Once the sub is neutral, the valves are closed and you're good to
go. Now, a "hard tank" is the same, but is stronger. Let's say you are adjusted
to neutral, and driving along submerged at 300 feet. There's not much pressure
in the tank, and it's half full, with the valves closed.
You come to an area where the buoyancy changes for what ever reason, and
the sub starts to float up. You want to add more water to the tank, so you crack
the water-in valve and add a little. The pressure of the surrounding water
compresses the bubble in the tank, and the sub gains a little weight. Again you
are buoyant neutral. You close the tank valves again to maintain that level of
buoyancy.
You're moving along and the sub starts to sink, so you want less water in
the tank. Read the surrounding depth/pressure on the depth gage, add some high
pressure air to the tank to just overcome the ambient pressure, then dump a
little water. Again, you keep the valves closed when not actively adjusting the
tank volume.
Now you've got some serious pressure in the tank, but it's
water volume is constant. OK, now it's time to end the dive and surface.
Use the motors to go up, not the tanks. Once you get near the surface, dump the
water from the VBT as it's already full of high pressure, and the water will
blow right out. now you're buoyant positive and the sub should float at the
surface. At this point, you blow the main ballast which raises the tower/hatch
as far out of the water as possible. If you just want to look around and go back
down, you wouldn't blow the MBT's. Save that air until you're ready to open the
hatch.
You've gone down and up, and still have most of your HP air in the scuba
tanks.
Now, if a situation develops where you want to go up really fast, then blow
the VBT at depth and still use the motors. Maybe give the MBT's a little squirt
of air to help, but be careful. A fast ascent can be very dangerous. If it's not
an emergency, use the motors to go up and down. Save the air as much as
possible. Blowing either tanks at depth and rising in the water column, the
bubble expands unless it's valved off.
This can lead to unsafe control issues. Frank D. A Good Credit Score is 700 or Above. See yours in just 2 easy steps! |