What if one connected a check valve in a pipe near the boats
hull (with the flow aimed outward) and used a hand operated piston pump
with long enough handle to apply enough force on a short stroke thin
diameter piston to expell water against outside sea pressure while at
depth to reduce the amount of water contained in this tank? When the
handle is again drawn back, additional water from this tank could enter
this piston. Once finished, isolation valves could be closed to prevent
additional water from
transfering.
&nb
sp; David Bartsch
> Date:
Tue, 21 Jul 2009 23:09:04 -0700
> From:
cast55@telus.net> To:
personal_submersibles@psubs.org>
Subject: Re: [PSUBS-MAILIST] water level
>
> Don't forget to
account for the possibility of having to adjust=2 0in the
> other
direction - i.e. adding buoyancy to compensate for reduction in
>
volume as the hull deflects at depth. For a small, shallow sub, this
> won't be significant, but as depth and the size of vehicle
increase, the
> change in volume may become significant.
>
> -Sean
>
>
>
ShellyDalg@aol.com wrote:
>
> Hi David. A sight glass is the easiest to read on a tank, but it's
not
> > much use to us for variable ballast tanks. The reason
being, it would
> > need to be able to withstand a lot of
pressure and they are hard to
> > keep clean.
> > The
variable ballast tank, often called "hard ballast tanks" are
> >
pressure vessels that will withstand being opened at depth to adjust
> > buoyancy when you're at your deepest operating depth, plus
what ever
> > safety factor you wanted.
> > Although a
simple "trim tank" can be used to adjust buoyancy at
> > or near
the surface, and then valved off with a set amount of water
0A>
> ballast in i t, no adjustment can be made when you're deep unless the
> > tank is able to withstand the pressure at your deepest
dive.
> > Once you open a hard ballast tank at depth, and close
the valves
> > to maintain that level of water, the pressure is
"locked" into that
> > tank. Then, when you g et back to the
surface, you release that
> > pressure by opening the valve and
letting the pressurized bubble blow
> > out the tank.
>
> If you want to adjust for more buoyancy at depth, due to changes
> > in salinity or maybe you picked up something from the
bottom, you must
> > blow high pressure air into the tank until
the correct water volume is
> > achieved, then close the tank
off to maintain that level of water.
> > Knowing just how much
water is in your hard ballast tank is a
> > problem.and one that
I considered a while back. The "sight glass"
> > method would
require a very heavy walled clear tube with valves in
> > case
it developed a leak. I'm not sure how risky that would be if it
>
> blew out but it should be fairly easy to build.
> > Another
method would be to use a "see through"tank. There's a
> >
filament wound fiberglass/composite tank available called "Lite"
>
> propane tanks and they come in a few sizes, the largest being about 8
> > gallons for use on warehouse typ e propane fork lifts. These
will
> > withstand 250 psi ( with a safety factor) and you can
tell at a glance
> > how much liquid is in it. They come with
threaded fittings molded in,
> > and a metal "basket" that
protects it from bumps. They run about $300
> > each I
think.
> >=2 0I'm leaning toward the see through tank right now,
and have a
> > place inside designed for it. That only gives me
64 pounds of variable
> > ballast though. ( 8 gallons at 8
pounds per). It would be nice to
> > have more adjustment, like
if you found something and wanted to pick
> > it up and bring it
back to the surface. It's possible to blow a little
> > air into
the "soft" ballast tank for lifting purposes, but that bubble
>
> will become much larger as you near the surface, making it difficult
> > to control buoyancy as your depth changes.
> > Most
psubs have a few lead bricks that get adjusted at the
> >
surface for how much payload you're carrying on any given dive, like
> > an additional passenger, some added machinery or cargo, or
what ever
> > will change the total weight of the sub.
>
> Buoyancy is based on water displacement and total weight in water,
> > so when you add a passenger, you must ask them how much they
weigh and
> > adjust the lead bricks according ly to achieve "
neutral" buoyancy. A
> > hard ballast tank is required for small
changes in buoyancy like
> > salinity and temperature changes.
For instance, if I launch my boat in
> > the harbor, which is a
river mouth with a small amount of dissolved
> > salts, and then
motor out into the ocean where the salini ty level is
> >
higher, the sub is displacing more weight ( the water is saltier so is
> > heavier ) so additional ballast must be added to maintain
"neutral. It
> > runs about 4% from fresh to salt water while
temperature can add about 1%.
> > These are percentages of
"displacement" or the total volume of water
> > displaced by the
submarine. Several "high dollar" subs I've read about
> > have
as much as 240 pounds of "variable" ballast. Not sure how they
>
> achieve that, but it's useful if you plan on bringing back samples or
> > stuff from down deep.
> > Frank D.
>
>
> >
------------------------------------------------------------------------
>
> What's for dinner tonight? Find quick and easy dinner ideas
>
> <
"http://food.aol.com/dinner-tonight?ncid=emlcntusfood00000009>;
for any
> > occasion.
>
>
>
>
>
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