----- 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.