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Hi Joe.
I agree with Rick. I would like to add though, that
some subs only have one set of tanks.
The ideal situation would be to have both soft and hard ballast tanks of course, but some
designs just use one set. Sometimes the soft ballast is not only used as soft ballast,
but
is also used instead of hard ballast
for trimming too. Some ambient subs such as the
silent runner 2 just use the air bubble in the
ambient cockpit as a ballast tank. That means
the cockpit interior upper bubble
functions as a single ballast tank for the whole sub.
I believe what Rick was trying to tell you is what
the different TERMS "soft ballast tank" and
"hard ballast tank" meant. He already explained the
primary function of the soft tank for freeboard
purposes, and the primary function of the hard tank
is usually for trimming the boat. That is
the difference between the two TERMS so that
everyone knows what they mean and what each
other is talking about when we say soft or hard
tanks. But it does not mean that a sub always has
to have both sets. Like the silent runner 2 it
could just have ONE single ballast tank. The explaination Rick
told you was like term descriptive meaning
purposes, it did not mean all designs have to have both or
even that they have to fullfill ONLY what would be
their normal primary function.
Did that help?
Bill.
Sent: Sunday, November 13, 2005 7:28
PM
Subject: Re: [PSUBS-MAILIST] Re: Variable
Ballast Calculations, Rick M
joe
the concept is
easy
soft ballst used on the surface to provide
additional boyancy for safe operationand crew egerss. the sub with these
tanks flooded flooded will still have a slight positive
boyancy
hard ballast used to provide negative boyancy and
depth control. normally much smaller then soft ballast tanks.
this is where it gets confusing hard ballast can
be either a hard tank ie able to withstand full working pressure or a
soft design that is open to the sea at all times and only has to withstand
2psi pressure
rick m
----- Original Message -----
Sent: Sunday, November 13, 2005 3:49
PM
Subject: [PSUBS-MAILIST] Re: Variable
Ballast Calculations, Rick M
Rick,
"the tanks they are
refering to are the soft ballast tanks.
which does not effect submerged
displacement"
Now I'm confused again. Just when I think I have
a concept down, bang along comes a problem. It's been a long day for me, I
need to take a break and review terms again later. I can't possibly do the
math now, info overload!
I will review what you're trying to tell me when
I have a clear mind again.
Thanks
Joe
From: "rick miller" <rickm@pegasuscontrols.com>
Reply-To:
personal_submersibles@psubs.org
To:
<personal_submersibles@psubs.org>
Subject: Re:
[PSUBS-MAILIST] Re Variable Ballast Calculations
Date: Sun, 13
Nov 2005 15:34:22 -0800
joe
the tanks they are
refering to are the soft ballast tanks.
which does not effect submerged displacement,
they effect surface displacement. soft ballast is normally free
flooding
the only time they effect submerged
displacement is durring emergency blow. but due to the large quantity of
air require to do this and the chance of an uncontrolled accent this is
not thee prefered method of operation.
lets look at what is
happening in the soft ballast tanks if you want to use them for a
controlled accent , for ease of the numbers we will use an accent for 66
ft or 3 atm absolute. fixed factors accent raate is basesd upon drag
and the positive displacement. we will use an accent rate of 60 ft
/min and a positive displacement of 128 or 2 ft^3.
durring the first thirty three foot rise
you will have to vent 1 ft^3 of air thru an oriface/ valve with a
differential pressure. in most tank designs this space would be
approx 1 inch allowing for a differential pressure of .03 psi ie a really
shitty flow rate.
for the next thirty three
feet of rise you will need to vent off 2 cf of air , while the air
density has decreased the flow is not linear based sloely on density
so you would have
to throttle the vent valves in order to made any kind of controlled
accent. this could be done using control valves and a pid controller
incorporated in a plc.but that waywould increase costs
dramatically.
the cheapest way to
accomplise this is to use a small trim tank open at the bottom that has
only the capacity to give a small quanity of positive displacement. as the
air in it expands it will just blow out the bottom. this method will using
more air the a sealed trim tank if you are planing multiple accents and
decents durring a dive but eliminates the need of a high preesure tank and
control system for the water intake valve. although it would require a
crew wiegh in to establish basic trim.
a standard scuba tank is
80 cf a 3000 psi/200 bar. assuming a full tank at 1000 ft or 500 psi
abient pressure. you will have a reserve lift capacity of
tanks size = .4 cf
volume air 80 cf air compressed to five
hundred pai ==2.35 cf
an available air supply of 1.95 cf or 125 lbs
of lift.
the formula is p1v1=p2v2
size of tank
80*14.7=3000x
80*14.7/3000=x
.392= x
3000*.4=500*x
(3000*.4)/500=x
x=2.4 cf total airremember the air that will
stay in the scuba tank
2.4-.4 = 2 cf of available air.
rick miller
Original Message -----
Sent: Sunday, November 13, 2005
1:28 PM
Subject: Re: [PSUBS-MAILIST] Re
Variable Ballast Calculations
Rick,
I had read in the NAVPERS manual for fleet boats, that a submarine
does precisely that to submerge, (reduce displacement by flooding the
tanks).
As for practicality, well this is all just math for now.
Incidentally, I am not using terms correctly in these posts, ie hard,
variable, soft ballast.
Thanks
Joe
From: "rick miller" <rickm@pegasuscontrols.com>
Reply-To:
personal_submersibles@psubs.org
To:
<personal_submersibles@psubs.org>
Subject: Re:
[PSUBS-MAILIST] Re Variable Ballast Calculations
Date: Sun,
13 Nov 2005 12:16:22 -0800
joe
you dont reduce
displacement by adding water. displacement = the total volume of all
non free flooding spaces.
the introduction of large internal
ballast tanks creates a sinificant engineering problem and a
possible piont of flooding for the passenger spaces. most hard tanks
are hard to inspect for corrosion. not to try to rain on your parade,
the kiss pricipal seems to be the way to go here, if you ever want to
get in the water.
rick
m
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