----- Original Message -----
Sent: Sunday, November 13, 2005 6:03
PM
Subject: Re: [PSUBS-MAILIST] Re: Variable
Ballast Calculations, Rick M
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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