Sub Design

[SFreihof@aol.com]

General discussion, sub design.... to all you Sub guys...

Thanks for your response, Gene.  I too am glad to have another afficionado
online to chat with.

Your flooded flashlight sounds like a desperate solution.  Seems to me that
even in fresh water, with all the connections flooded internally, you're
going to have some current drain as shunt to ground shorts.  It may not be
too severe in fresh water, but I'm sure that in salt water you'd drain your
batteries and corrode your flashlight pretty darn quick.

I'm hoping I can help you with your sub design.  I'm not an engineer, but I'm
pretty knowledgeable in sub design, because I've studied it for quite a while
now.  There are four basic designs for you to choose from.

1.  A wet sub:  It is basically a Diver Propulsion Vehicle (DPV), much like
an underwater scooter.  You are immersed.  The sub serves to propel you
through the water with all of your scuba gear on. Scuba depth/time limits
apply.

2.  A Semi-dry sub:  It is basically a bubble contained in the cabin.  You
sit in water with your head (and maybe shoulders) in a bubble of air within
the cabin.  Often, the bouyancy of the sub is controlled by adjusting the
level of water within the cabin.... the cabin serves as a ballast tank.
 Scuba depth/time limits apply.

3.  Ambient Pressure Dry Sub:  The cabin is dry, but air pressure within the
cabin is regulated to always equal the external water pressure.  There is no
pressure-differential across the hull, and the cabin is entirely air filled.
 Scuba depth/time limits apply, because you are still breathing air under
pressure... 

4.  Pressure Hull sub:  The hull is designed to withstand increasing water
pressure with depth.  Such designs have a bottom limit or 'Crush Depth'
beyond which the hull may implode, but pressure within the hull rarely
exceeds surface (1 atm) pressure under normal operation.   This requires a
very strong (and therefore heavy) hull design.  This is the most familiar
design, used in virtually all military submarines.

The complexity and cost of building a sub will increase almost exponentially
with each step from 1 to 4 in these designs.

The design I am working on is #3, ambient pressure dry sub.  This seems to me
to offer the most advantages, although there are disadvantages also.  Wet sub
are the lightest.  You only have to provide enough bouyancy to compensate for
the weight of the sub and equipment/machinery.  The semi-dry is next.  The
air volume is relatively small, so it only has to be heavy enough to sink a
small air bubble.  The Ambient-Pressure Dry sub weighs more, because it has
to be heavy enough to sink the air contained within the cabin, and you have
to design in enough weight to sink the bubble. Generally, the Pressure Hull
sub is the heaviest, because of the material strength required to withstand
external pressure.  With these subs, it's a matter of building in enough
floation to compensate for the inherent weight.

With all of that said, I have opted for the Ambient Pressure Dry design.
 Keeping the cabin volume to a minimum keeps the weight to a minimum... you
only need enough weight to sink the air volume of the cabin, and the benefits
of a dry cabin can be substantial.

So I'm curious what design you are contemplating.  I may be able to help, but
I can assure you that from what I have seen and heard in this discussion
group, there are others who are much more qualified than I am to give advice.

The point I find here is a love for subs and a willingness to share ideas and
information.  I hope to learn and to share with all of you.

Stan Freihofer
SFreihof@aol.com