[PSUBS-MAILIST] AMBIENT DRY SUB

[SFreihof@aol.com]

Hi Rob;

Ambient means "surrounding".  An ambient pressure sub is one in which the 
interior of the sub is at the same pressure as the exterior.  Since there is 
very little pressure gradient, the hull doesn't need to be designed as a 
pressure hull.  That gives you more options in your choice of  hull materials.

A wet sub is an ambient sub,  but ambient subs can also be designed dry 
inside, as long as the air pressure inside the cabin is the same as the water 
pressure outside.... that is to say, as long as the air inside the sub is at 
AMBIENT pressure.  In an ambient dry sub design, the hull essentially 
confines a bubble, but not pressure.  

Get in a pool.  Take a glass and turn it unside-down.  Now, push it 
underwater.  The air is trapped in the glass and can't get out.  If you push 
the glass deeper in the water, the bubble in the glass will shrink in size 
(and so you see the water level rise in the glass) because water pressure is 
increasing as you go deeper, and as you increase pressure on a gas, the 
volume will decrease.  This is stated by Boyle's law which essentially says 
that pressure and volume are inversely related:  If you incerease one, the 
other decreases; and if you decrease one, the other increases.

Since the volume of a dry sub is constant, you accomodate Boyle's law by 
adding air to the cabin as you descend and bleed air out as you rise, so that 
the cabin volume is constant and air pressure is adjusted so that it is 
always AMBIENT, or equal to the water pressure outside.

This sounds harder than it is.  Essentially, a scuba regulator does exactly 
that.

There are limitations to the design.  Since the cabin is pressurized, you are 
breathing air under pressure, and thus you have the same depth/time 
limitations as a scuba diver.  I would never recommend that anyone dive an 
ambient sub unless they are a certified scuba diver, because all the same 
rules of physics and physiology apply. GET CERTIFIED.

Most of the contributors on this site are building pressure hull designs, 
which are called "1 ATM" subs.  This is technically demanding and beyond the 
knowledge, skills, and abilities of most tinkerers.  The advantage of an 
AMBIENT dry design, is that essentially all you do is build a bubble.

My recommendation is to work within your abilities.  Know what your 
limitations are and stay within them.

Stan



  



In a message dated 2/18/00 11:26:49 AM Eastern Standard Time, 
divine@kconline.com writes:

<< Im not shure what the term"ambient" means.  But a dry sub is exactly what
 I am looking to build.  I hear that term used often, but no one ever said
 what is means. >>