Re: ambient preference

[Rick Lucertini <empiricus@sprint.ca>]

Alex Wolfe wrote:

> [snip]        What scares me the most is the descent portion... from what I
> understand (am I correct??)
> most dry ambient "subs"
> just use a free-flow air delivery system to vent the cabin (and keep
> your air pocket to the level of the pipe/hole/whatever).  If you begin
> to descend faster than you can compensate for decreasing air volume you
> can either sink uncontrolably or drop some weight and go "pop" to the
> surface (from depth and pressue no less).  I guess this is what scares
> me.  Does anyone have any insight on this?

Hi, Alex.  I just posted to Stan's query about the same question you have.  It
answers yours, as well.

By isolating the cockpit from ambient water and pressure, you reduce the chances of
Boyle's Law causing any problems.  Of course, compensation still has to occur and
good, stiff walls are a must.  There WILL be some differential and the walls have to
be able to deal with that.

> Alex
>
> P.S. there's a link to an ambient sub maker from the "links" section on
> the psubs page.  i forget the name of them, but they advertise some
> kind of "electronic" control for bouancy issues.

The Manta's (I think that's the link - just going by intuition, here) buoyancy
control valve's design was, I believe, commissioned to a fellow by the name of Hugh
Dasken.  Hugh gives (used to?) a course in submersible design here in Vancouver.
He's been involved with a number of u/w designs.

I have a personal bias toward minimizing the use of electricity u/w especially in a
marine environment.  While Hugh's design works from what I've heard, I would prefer a
mechanical device like a differential pressure valve or diving regs.

Of course, a diving reg cannot admit very much air into the cockpit, so descents
would have to be slow.  This in itself could present a hazard in that an uncontrolled
descent could collapse the cockpit before the regs could admit enough compensating
air.  A go-around would be to have several regs in a manifold or W.H.Y. and a
stiffened cockpit walls.  As in, one inch marine ply.  Not too professional.  The
other way is to buy an industrial differential valve designed to handle the cockpit
volume at a rapid rate of compensation.  The chances of a freeze-up would be reduced,
as well.

Rick



--
Rick Lucertini
empiricus@sprint.ca
(Vancouver, Canada)