|
Frank, That is what I was alluding to when I answered the first
thread. Hugh. From:
owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]
On Behalf Of ShellyDalg@aol.com The thread started by Jens reminded me of a question that pops
into my head sometimes...... First off, with the sub at neutral buoyancy it's correct procedure
to "drive" to the surface before blowing ballast. But....... If a sub is down say 300 feet and the pilot wants to ascend, and
he dumps a little air into the soft ballast tanks to begin rising then as
the sub rises the bubble will expand and push more water out the open hole. The ascent rate would increase as more water is pushed out by the
expanding bubble. The more you ascend, the faster the bubble expands, and the
faster you ascend. Some questions come to mind. Can the ascent rate become so fast that a large pressure differential
builds up between the water pressure outside and the ballast tank pressure
inside the soft tanks. If the water can't get out fast enough the pressure
could build up inside the tank as the bubble expands, and it could damage the
relatively thin soft tanks. The pilot could open the air release valve on the ballast tank but
if the holes in the tank bottoms were too small, a pressure differential could
develop. What is the right ratio of ballast tank air vent and water inlet holes
? How is this ratio calculated ? Would it make sense to have a pressure gage inside the ballast
tanks so a comparison between ambient pressure and tank internal pressure could
be observed ? If a pressure differential developed because the ascent rate was
overcoming the ballast tank's ability to dump the water, it would be necessary
to open the ballast tank air vent valve to release the pressure. Most soft ballast tanks are made from sheet metal and not meant to
handle much pressure differential. Frank D.
__________ Information from ESET NOD32 Antivirus, version of virus signature database 5125 (20100518) __________ The message was checked by ESET NOD32 Antivirus. http://www.eset.com |