----- Original Message -----
Sent: Saturday, October 29, 2005
2:49 AM
Subject: Re: [PSUBS-MAILIST] Hard /
soft ballast tanks.
Hi Myles.
Hard ballast and soft ballast have nothing
to do with hardness. Here's an article that may explain it to
you.....
When a submarine is on the surface, its "soft" ballast tanks are
full of air. These tanks are mounted high along each side of the hull,
and are open to the sea at the bottom. Air is forced through valves at
the top of the tanks, which displaces sea water and gives the submarine
its surface stability and a minimum of 30" of freeboard between the
water line and the top of the hatch combing. When the pilot is prepared
to dive the submarine, he actuates exhaust valves in the top of the
tanks which vent the air and allow the sea water to fill the tanks
again.
Differential ballast is provided
by the "hard" ballast tanks which
are designed to allow the submarine to achieve weightlessness or
"neutral buoyancy" when it's submerged. The hard tanks must be
filled with sea water if the submarine has just a few passengers, and
they are empty if the vehicle is fully loaded. Water can be pumped back
and forth between the bow hard tanks and the
stern hard tanks
to adjust the trim of the vessel. Some vessels also have a trim weight
beneath the pressure hull that can be moved back and forth on a track to
provide pitch trim.
Safety
Contemporary tourist submarines have a perfect safety record, having
carried in excess of 7 million passengers without a single serious
injury or fatality. Much of the credit for that safety record goes to
the American Bureau of Shipping, an organization that "classifies"
marine vessels. The ABS approves the submarine design and engineering,
insures the safety of the materials used during construction, tests and
inspects the various submarine systems, and attends the vessel's sea
trials. Ongoing annual inspections are also required.
In American waters the United States Coast Guard duplicates much of
the work done by the ABS, and also stipulates requirements for the
experience levels and licensing of the submersible crew, insures the
existence of adequate documentation, and enforces compliance with a
substantial body of safety regulations.
In the event of an emergency, the pilot, who is in contact with the
surface by underwater telephone, may employ a number of safety features.
The submarine has an automated Halon fire extinguishing system, and each
passenger has a closed system rebreather for use in case of a fire that
is capable of providing oxygen for a minimum of two hours. An emergency
ascent can be accomplished by 1) blowing high pressure air into the soft tanks, 2)
dropping an emergency drop weight composed of several tons of lead ballast, 3) blowing
the hard ballast tanks full
of air, and 4) using the electric vertical thrusters. As an additional
aid to safety, no tourist submarine may operate in waters deeper than
its maximum design depth, typically between 150' and 328'.
You are correct Myles about the ballast tanks
being as ambient when flooded or blown. One thing you can do is have the
bottom of your ballast tanks open so the air can spill
out
if you overblow them like in the kittridge
K350 sub. Some guys fill in the bottoms almost all the way but leave a
hole for excess air to spill out. That way they don't "burp"
as
much from air spilling out of them when you
don't want it to like in choppy water. Remember, the air always goes up.
So you can put an overpressure valve in your tank to
vent the excess air or you can just make a
hole in the bottom. Does the same thing except the hole can't fail on
you like the valve can. Also you could use a sliding weight
under your keel in place of or along with
hard ballast tanks. For instance, you could use a long piece of
stainless steel threaded rod. Then attach a weight to it so that when
you crank the rod it moves the weight back
and forth under the sub for trimming it out. I have been thinking of
making something like this for my wetsub instead of using hard trim
tanks,
but I haven't made up my mind on that yet.
I would suggest for your ambient design having both so in an emergency
you have extra tanks to blow if needed. In my wetsub it is not
as
critical because I can easily bail or use
my personal Buoyancy control device (BCD) for extra lift if necessary.
Hope this helped you.
Bill.
----- Original Message -----
Sent: Friday, October 28, 2005
8:36 PM
Subject: [PSUBS-MAILIST] Hard /
soft ballast tanks.
Gents,
Hard / soft ballast
tanks....what exactly are we talking about here ? Hard ones made
of...hard material and soft ones made of inflatable bags or something
?
In contemplating my design
for the fore and aft main ballast tanks, it occured to me that
the construction of these tanks does not have to be up to the same
standard as the pressure hull, even if purged at depth, due to the
fact that the forcing of air into the tanks to purge the water creates
an "ambient" enviroment within the tank, equalizing the pressures put
upon it. Is my line of thinking correct ? In other words,
as far as the ballast tanks are concerned, it shouldn't matter if
the internal and external pressures are equal due to the tank being
filled with water, or compressed air. As long as your high
pressure air supply has enough psi to force the water out, it should
be possible to blow the tanks at any depth. Again, am I on the
right track with this thinking ? One of the reasons I am
enquiring about this is I am wondering if it's possible to use
fore/aft main ballast tanks as trim tanks as well ? For eg. if
I'm at a depth of 50M in my 1ATM sub (with fore/aft tanks filled with
water), and I discover that my trim isn't quite right, that I require
a little lift in the front, can I put a little air into the fore main
ballast tank, or will this damage the tank since the construction of
it is quite light. I suppose if it is possible to blow the tanks
at any depth, you would want some sort of check valve to bleed off the
excess pressure that would occur from surfacing, or risk blowing your
ballast tanks up, sinking, and dying.
Myles.