[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 -----

From: Joseph Perkel

To: personal_submersibles@psubs.org

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

************************************************************************ ************************************************************************ ************************************************************************ The personal submersibles mailing list complies with the US Federal CAN-SPAM Act of 2003. Your email address appears in our database because either you, or someone you know, requested you receive messages from our organization. If you want to be removed from this mailing list simply click on the link below or send a blank email message to: removeme-personal_submersibles@psubs.org Removal of your email address from this mailing list occurs by an automated process and should be complete within five minutes of our server receiving your request. PSUBS.ORG PO Box 311 Weare, NH 03281 603-529-1100 ************************************************************************ ************************************************************************ ************************************************************************