----- Original Message -----
Sent: Saturday, February 11, 2006 11:54
Subject: [PSUBS-MAILIST] Hybrid for Joe?
and hatch installation.
I have a couple of ideas for you.
First idea....I know that you said previously
that your intent for the octopus is to use it a lot as a surface boat that
will occasionally dive to shallow depths as an ambient sub.
After posting my last post about using propane
tanks to create a hybrid 1 atm/ambient system, I am wondering if you could fit
a small propane tank into your sub design that would allow you
the other person to still seat in tandem. Since
you plan to only dive to shallow depths anyway, this way you could operate as
a 1 atm sub to perhaps 2 atm and not have to worry about dive
Then if you did decide to go deeper you could do
that also by the system automatically switching to ambient operation beyond 2
atm of depth. The advantage of this over you just making the
strictly ambient is that if you don't plan to
dive very deep most of the time anyway, it wouldn't automatically pressurize.
That means you would not have to worry about the problems of accending
fast after being down a while which can give you
the bends (decompression sickness) as long as you did not go deep enough for
the valves to automatically switch to ambient operation.
when operating an ambient sub your body is under
the same pressurization as if your body was at that depth in the water. This
is one DISADVANTAGE an ambient sub has that a 1 atm sub does not
because a 1 atm sub can rapidly pop to the
surface without any ill effects to your body. This would afford you a margin
of safety in that you would not only NOT have to worry about dive tables, but
you would not have
to worry about emergency accents or unexpected
accents that could injure your body if done too rapidly in an ambient sub. I
thought this might be a good thing for you to consider Joe.
Go to his site and look for the contents heading
of "Evolution of Design". Then scroll down to just a little before the bottom
of the page and you will find this paragraph.......
"5. The hatch was designed to open outward after testing in a card board
mock up, but now that I can test with the real cabin, it is easy to see that
opening it inward is not really a problem. And opening it inward is much
easier to seal and safer, since the pressure on the hatch when submerged
naturally wants to push the hatch outward. This is a trait of ambient
submarines and opposite of their 1 atm (atmosphere) cousins."
If you do decide to build the octopus to be
strictly an ambient sub, you might think about if you would want to install
your hatch to open inward as he has. Since an ambient sub has internal
pressure that pushes outward against the interior of the sub's
Doug reasoned that the hatch would seal better
when closed if designed to open inward. If you ever got stuck on the bottom
and had to bail out of your sub, you would have to open your scuttle valve and
use a bail out tank and wait for the water to enter your sub
and equalize the pressure so you could open the
hatch inward. You would have to do this in a 1 atm sub too. The only
difference would be that with the ambient sub's hatch opening inward, your
internal air pressure is pushing it against its flange seal, whereas in a 1
atm sub the water pressure is pushing it the opposite way against its
I didn't know if you had considered the
differences regarding hatch installation between 1 atm and ambient systems
That is the end of my two ideas for you. But now
I have a question for myself and others here. Since it is easier and safer to
open an ambient hatch inward, as opposed to opening a 1 atm hatch outward, how
would someone install a hatch
that would go on a 1 atm/ambient hybrid sub like
I have described previously? Sometimes you may only use the hybrid as a
1 atm sub for a given dive. Other times you may decend a bit deeper and
automatically switch to ambient operation.
Which way would someone install the hatch in
this situation? This one has me puzzled. Anyone have any idea?