[PSUBS-MAILIST] Trim Tank Idea

["Harry Spillett" <harry.spillett@bigfoot.com>]

Hi Guys,

I am still trying to fine tune my understanding of the pros and cons of
various designs. Can I have your views on the following:

In my quest for knowledge on everything submarine I have bought a book on
model submarines. It seems that most employ a "diving cell" as a version of
MBT. A common method employed by the modellers is a "piston tank".

As the name suggests it is a cylinder designed to withstand diving pressure
containing a piston and suitable seal on a threaded shaft. The shaft is
cranked in and out of the cylinder rack and pinion style with a heavy duty
servo. It is also common to have a rotary pot fitted to the shaft to
indicate the volume of water in the cylinder either for auto depth
correction gear or simply as a bar graph.

My question is could a similar design be used (on small PSUBS) as an
accurate "air free" trimming system. You could have one fore and aft and one
amidships used like a VBT. If a suitable motor was used (electric or
hydraulic I guess) it could be made to compress the trapped air behind the
piston (rather than vent into the pressure hull like the models, this may
help the seal stand up to diving pressure too, I am on a roll now!). Like
the modellers you could have a sensor on the shaft to feed an  automated
control system or more likely a relative bar graph display.

Have I just reinvented the wheel or is this a viable possibility!

Harry