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Re: [PSUBS-MAILIST] Hard ballast tanks.



If that's what you want you need to have 1atm ballast tanks that are totatally sealed off from the outside environment and make sure you are neutrally bouyant at the surface. (Depending on your mission depth, you may have to take into account the compressability of water and your hull and be slightly positively bouyant and power yourself down). which means that you lose the ability to use ballast to control your position in the water column and must power yourself up or down. You'd of course have a drop weight for emergencies and possibly a compressed air emergency blow system, but This all seems something that is rather complex for a submersible that's operating range is probably going to be limited a very great deal without surface support. (You can only run your motors so long on battery power, and diesel bunkerage on a submersible the size that's generally associated with a PSub would be... negligable)

Doug Jackson has the closest thing to an independant submersible/submarine I think I've seen so far... you can see his stuff at www.submarineboat.com (Note, I stole his moveable keel weight idea to stabalize Archimedes' manipulator). So if you're thinking about building something that can get itself to the dive site, then his idea might be something to look at.

Autonomy is a laudible goal, depending on your project size and what your doing with it you either have to go very large or very small (AUV/ROVs) to do it because your power requirements either need to be met via having the bunkerage (Large) or they have to be designed to draw as little as possible off of a limited power supply, a mere "trickle" compared to the needs of a manned craft.

Thrusters of course are one of the largest drains on power.. (the are THE largest drain in my rov projects) on a submersible powered by Minkotas something far far larger than the small DC motors I use, you're looking at major power requirements, that you could possibly offset with a Diesel engine/generator, but that's not as efficient as having a straight through diesel to screw arrangement, which means you're going to need to have some sort of transmission setup that can be switched to have the mechanical power of your diesel engine either power the main drive shaft, the generator, or both.

This is not to discourage you, just to illustrate some design considerations and give you something to think about.

George H. Slaterpryce III
www.bridgessoftware.com
www.captovis.com
----- Original Message ----- From: "kory mosteller" <hardcoremosteller@hotmail.com>
To: <personal_submersibles@psubs.org>
Sent: Thursday, December 07, 2006 12:39 PM
Subject: RE: [PSUBS-MAILIST] Hard ballast tanks.


Good points Gene. I think the goal i've been striving for is to make my sub as autonomous as possible. It's more of a personal achievement kind of thing for me than a truely practical one. AS a kid, i never said to myself "i want to be a SUBMERSIBLE captain"... it was always SUBMARINE. In a full size diesel electric, all you would ever need would be food and fuel. Leaving the diesel part out, (but retaining the electric compressor and batt chargers) all you would need is electricty and food. for me, that means that ANY large vessel can be a support craft as all i would require would be somewhere to plug in an extension cord. Adding and subtracting lead, you may find yourself asking "excuse me, do you have any lead i can borrow?" Kind of an extreme silly example i know, but i think you get the picture.
-kory






From: HUNTR2@aol.com
Reply-To: personal_submersibles@psubs.org
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] Hard ballast tanks.
Date: Thu, 7 Dec 2006 03:16:41 EST

Hi Kori,
Welcome to the group.  I, also live in the "land of fruits and  nuts!"
I think you have it understood pretty well. I also want to have the option of increasing buoyancy to neutral with a shot of air to purge the hard trim ballast tank a little if I take on additional weight. Additional weight could be from accidentally letting too much water in the trim ballast or picking something up with the manipulator arm. If you don't have an air purge capable
hard trim tank, then the only option is to put some air in  the MBT.  Once
you do that, neutral buoyancy becomes a challenge if you want to descend or
ascend very much without surfacing.

Yes, to have larger hard trim ballast tanks is doable, just more structure
and plumbing required. They can be inside or outside the hull. If they are inside, they have to handle internal pressure safely. If outside the hull, they better be able to withstand the external crush pressure or have automatic pressure compensating air available. If a large one crushed at depth, the
results could be scary and perhaps tragic.

It's interesting to note that those with actual pilot experience aren't
saying that large TB tanks are important. Leaving lead at home means you have a smaller internal sub to start with and having large trim ballast tanks to use when taking passengers just makes the sub larger (greater displacement) to handle the extra load. The space in the tanks is not functional for living or using for anything but buoyancy, weather you are using them or not. In effect, what you have done is limit usable internal space in single person mode in exchange for not carrying lead. If you're pulling a 5000 lb submersible,
another 180 lbs of lead isn't too big of a  deal.   (Less than 1% of the
total weight).

Gene
Central Ca.

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603-529-1100
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