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Skeet,
To remain neutral in the water, you have to set the
weight of your sub is exactly the same as the water it displaces, any more and
you go down, any less and you rise.
Design your sub about ten percent lighter then it's
displacement, then later you can add lead to trim to dive weight. If you
decide you want to add some new gadgets later on, you still can by just removing
some lead. Better too light then to heavy and have to add floatation to
the outside. Once you have the proper amount of lead on board, fine
tuning your displacement is done with your variable ballast tank.
Dan H.
----- Original Message -----
Sent: Thursday, March 02, 2006 11:10
AM
Subject: Re: [PSUBS-MAILIST] ambient
ballast control
Thanks Dan (and all) - This is very
helpful. I did not realize the numbers had to be so close. I
assume that the larger the boat, the further off you could be and still
operate. However, it sounds like a very critical measurement to work
around.
Skeet
----- Original Message -----
Sent: Wednesday, March 01, 2006 9:01
PM
Subject: Re: [PSUBS-MAILIST] ambient
ballast control
When I dive Persistence, I dive it neutral
buoyant. There is an additional safety factor if you dive slightly
positive but you can't stay in position near the bottom without
constantly fighting the lift. If I want to ascend quickly without
electrical power I just give a short burst of air into any of the ballast
tanks. Normally I descend and ascend with thrusters.
Once, I let someone dive solo in my sub.
He was familiar with the sub but I coached him through the diving sequence
from topside on the radio anyway. I had him set about five pounds
positive. It was relatively shallow and he couldn't get into much
trouble being positive buoyant as R/Jay mentioned.
If you were fifty pounds positive, I doubt you
would be able to get your sub to submerge. Fifty pounds of downward
thrust is a lot to generate! There is a lot of mass to the sub so
things happen slow but five pounds heavy or light will make the
sub move up or down nicely. Ten pounds moves you a little
faster. If you were only going thirty feet to the bottom five pounds
is enough. If you were going two hundred feet down, more weight
would get you there faster.
Your ballasting system doesn't have to be able
to adjust a lot. I move lead weights in and out depending if I have a
passenger and how much they weigh. I have 20 LB, 10 LB and 5 LB
weights. A total of about 400 Lbs. of lead. My
variable ballast tank is only about 35 pounds in total.
My favorite way to dive is neutral and drifting
a few feet above the bottom. It's really quiet when the sub is
drifting and only powered once in a while.
Dan H.
----- Original Message -----
Sent: Wednesday, March 01, 2006 11:33
AM
Subject: Re: [PSUBS-MAILIST] ambient
ballast control
As for buoyancy - Does anyone have a feeling
for how much "positive" bouyancy your submersible should maintain at
depth? For example, if you are displacing 3000 pounds of water and
you weigh 2800, will you be able to power under with dive planes and
motors? Do you have to be at 2950? Are you dangerously over
neutral at 3100? I know ideally that we should be right at
the numbers - but doesn't the ballast system give us some
variability? I am intending to build a two man sub - and that
means the weight will not be the same for
each dive. Are there published "rates of ascent" tables or
percentages figures we can use in our calculations?
Skeet Stribling
----- Original Message -----
Sent: Wednesday, March 01, 2006
8:25 AM
Subject: Re: [PSUBS-MAILIST]
ambient ballast control
Typically the main ballast tanks should be flooded fully and the
flood valves at the bottom of the tank left open (or in the case of a
K-250, the bottom of the tanks are open). To dive the hard (rated
to max. pressure sea and/or blow system failure) is then flooded to get
either neutral or slightly positive trim. Submergence is
accomplished with dive planes and drive down with the main motor(s) (and
in the case of a K-350, additionally using the auxilliary motors).
Being slightly positive will benefit in the case of a loss of power as
the sub will slowly return to the surface on its own.
A normal surfacing evolution is accompllished by powering to near
the surface and them blowing main and trim ballast tanks thus conserving
the limited supply of air carried aboard. Only in an emergency are
main and trim tanks blown at depth (and then dropping the emergency
weight if neccessary).
R/Jay
-----Original Message-----
From: "Dan H."
Sent: Mar 1, 2006 8:39 AM
To:
personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] ambient
ballast control
Joe,
What I was questioning is the need for a
pressure relief in a closed ballast tank where the tank is built strong
enough to withstand the system pressure. If your tank is strong
enough to withstand the system pressure, then it won't blow.
As was pointed out to me by Jay, it's still
possible to get a regulator failure, and unless the ballast tank was
built to SCUBA tank pressure, it could possibly be ruptured if that
happened. Good point. My sub is a one atmosphere
design.
That is the one scary thing about an open
ambient sub. Then deeper you go the more air it takes not to
go any deeper. A situation that can be a runaway disaster.
I don't know about an ambient sub, but
in my one atmosphere, when diving, I keep my main ballast
tanks totally full of water , vents opened, and my main ballast
tank, adjusted to neutral buoyancy of the sub and all valves shut.
Dan H.
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