Re: RES: [PSUBS-MAILIST] Ambient pressure design considerations

[SFreihof@aol.com]

Hi Jorge;

 

To be correct, the Sport Sub is an ambient semi-dry sub.  It is not a dry sub any more than it is a wet sub.  The cabin itself serves as the ballast tank, and the water level in the cabin determines its buoyancy.  You sit in water with your head in a bubble.  There is no hatch.  The bottom is open.  To enter the sub you have to dive under it and swim up into it.

 

Conversely, an "ambient pressure dry" sub has a dry cabin.  The term both describes and defines the design.

 

The Sport Sub has a 'continuous flow' cabin air flush, but the drawback is that the air consumption is high.  The flow rates required per person have been studied in underwater habitats and are detailed in the NOAA Dive Manual which I can look up for you if you'd like.  The point is you have to carry a lot of air to do it.  Breath moisture is a minor consideration because you are operating in a humid environment with warm air encapsulated in a cool shell.  Condensation is unavoidable, so plan on it.

 

Stan

 

 

 

In a message dated 11/2/2003 3:57:22 AM Eastern Standard Time, jorloujr@uol.com.br writes:

Hi, Dave !

Being a hard-core full time lurker myself I'll dare this time to disclose MY
deep ignorance, following your (good !) example:

I think that there is no point building a sub where you are wet and wearing
a mask (yeah, I recall your saying DRY, but I'd bet it's gonna be a semi-dry
vehicle due to ballasting issues...). The only justifiable thing I can see
in this approach is  the protection against some environmental hazards
(sharks ?). We'd be better off diving donning the regular diving gear and
being pulled by a scuba tow. That means a lot of speed, greatly extended
bottom time and unsurpassable freedom of movement. And a lot cheaper, let's
not forget ...

If I ever build an ambient dry submersible I'll mimic the SportSub [
http://www.ivccorp.com/ssinfo.html ] and the Markham Wing [
http://www.psubs.org/pic/wet.html ] designs, for instance.

The SportSub features a continous flow air feeding device that sweeps away
the stale air and besides that has the advantage of providing a rebreathing
effect that circumvents the oxygen waste of a scuba (open circuit) gear
extending bottom time about four times. This is not to be despised. By the
way, CO2 buildup is not a concern, if you are not diving for hours, even in
the K-250, where the breathing air is what is entrapped inside the hull when
the hatch is closed, and moisture condensation will happen anyway, requiring
more than fresh air to be avoided.

The Markham Wing has a simple pipe pivoting around its elbow to set the
water level inside the "cabin" thus controling the buoyancy.

Both devices are very simple, easy to build and operate, reliable and cheap,
fully adhering to the K.I.S.S. principle, leaving little to be desired.

That's it for now, hope it helps...

Jorge L.