[PSUBS-MAILIST] Ballast Explanation

["Jon Wallace" <jon@psubs.org>]

I found an article written by Dr. Sylvia Earle describing "Deep Rover" and
how it works.  The article includes the following description of ballast
usage which I consider to be very straightforward and easy to understand.
I'm going to add this to the webforum as well.  The full article can be
found at:
http://www.usc.edu/org/cosee-west/MidwaterRealm/14SSEbackground.pdf


## START QUOTED MATERIAL
In order to regulate its position up and down in the water and to remain at
a certain depth without rising or sinking, DeepWorker uses two forms of
ballast systems??soft? ballast and ?hard? ballast.  Many submersibles use
what is called a ?soft? ballast system in which compressed air is released
into an external tank to increase the craft?s buoyancy and bring it back to
the surface. At deep depths, air becomes so compressed by water pressure
that it can take an entire tank to lift the sub off the bottom. In these
systems, such as the Deep-Rover submersible, pilots must limit their up and
down movements at depth to conserve air for the final ascent.

DeepWorker uses soft ballast together with another ballast system known as
?hard? ballast. In the hard ballast system, colored water is contained
within an enclosed small bladder outside the sub. After the pilot dumps all
the air from the soft ballast tank in order to lower the sub below the
surface, the sub remains slightly buoyant. To sink, the pilot opens a valve
to allow a small amount of the colored water into the sub, which adds
weight. The water begins to fill a tank in the pilot?s seat, and the sub
descends.  When the sub is neutrally buoyant (neither sinking nor rising),
the pilot shuts off the valve. This ingenious design allows the pilot to
remain neutrally buoyant at any depth. Pilots can tell when they are
neutrally buoyant by looking at minute particles drifting outside in the
water column.  When the sub hangs motionless in relation to the tiny
organisms and debris that make up the ?marine snow,? the sub is neutrally
buoyant.
##END OF QUOTED MATERIAL





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