Greetings James,
"1. If the ballast tanks were to totally surround the crew
compartment, could the ballast area be used structurally?
I mean if the air were purged, then the ballast area totally sealed (with valves). Would this enhance the structure to help with the pressure at depth?
I figure since this area would be totally filled with water
(which doesn't compress easily) it would add pressure resistance of
the hull. (I'm only guessing at this......so anyone could point out
the error in my view)"
The water isn't compressible that is in the ballast tanks, but the hydrostatic pressure is still trying to compress the air in the crew compartment. So if the ballast tank hull can't take all the pressure, it will transfer the remaining load to the inner hull. But first a small amount of pressure must press in on the inner hulls air before the outer hull will start to hold back the hydrostatic pressure, if there is no compressible air and/or gas in the ballast tank. If there is compressible air and/or gas in the ballast tank, the pressure would first start to compress that air and/or gas then the outer hull would start to hold back the pressure. In the last scenario, the small amount of pressure applied to the air and/or gas would press against the inner pressure hull along with any outer hull supports and/or flanges, that connect the outer hull to the inner hull that transfer some of the pressure applied to to outer hull to the inner hull. Also the weight of the water in the ballast tank would apply some small force against the inner hull, the highest of this, at the bottom of the inner hull.
I would say it would be like using the ballast tank that completely surrounds the inner hull, some what like a hard variable ballast tank (VBT), or letting the tank completely fill with water and have one or more VBT's, inside or outside the crews pressure hull for fine control of buoyancy. If you use your larger (sealed with valves) main ballast tanks as your VBT, then the air in it is compressible, unless you use a vacuum for the buoyant force in the tank and not air and/or gas. If you use a vacuum, then your ballast tank and inner hull has to be designed to with stand the amount of negitive PSI the vacuum is set to on the surface and submerged. I wouldn't expect that not to be much of a problem for most hulls, but it has to be checked off. Also I would expect you would need a high pressure electric pump to add and remove the water while maintianing a vacuum. The vacuum could be maintained with an electric vacuum pump like used in infusion molding composites. Using a high pressure pump for adding and removing water from said tank would likely make submerging and surfacing slower unless you get a big pump.
I don't see any real advantage to having a vacuum in this type of ballast tank. I would just leave some air in the tank to be slightly compressed and design the inner hull to be as strong or stronger as the outer hull.
Using the ballast tank as your first line of defense against hydrostatic pressure could be good if your inner crew hull is as strong or stronger in case the outer hull fails or a valve fails, as well as other reasons. Also if the outer ballast pressure hull has a collision with rocks, boats, and other subs, you have a backup pressure hull to protect you from the hydrostatic pressure and/or the object that damaged the outer hull in the first place. I may have some holes in my logic on this whole matter, so I hope the group double checks it for us.
" I know totally encapsulating( mostly.....the top hatch could
never be totally surrounded) the crew compartment within a ballast
area would be a major pain, and would be hard to up keep over a long
period of time, but it may be worth the while if the design is
possible."
I think it is possible, but you would most likely need a second hatch. It would be sorta like having a submarine inside a submarine and in so doing could be a very safe design. As for maintenance, I see allot of ways in designing it in unbolt able sections that it would be just fine.
"2. I've noticed a very strange item on the X300( nice fiberglass
single place, dolphin shaped sub) aft end. I'm very curious what the
item is. I would also like to know what type of propulsion the sub
uses."
Cliff would be the best one to answer this, but basically He's using a jet ski type squirt drive powered my an electric motor, which is run off of deep cycle batteries in a very clever configuration.
3. Are there any electronic valves out there that are pressure rated
for our uses. I would like some companies to checkout to see if I
can use them for ballast control.
This is an area I would like to know more about myself. I'm looking at using pneumatic valves I've seen used on the Alicia submarine. Here are some pics of the Habonim pneumatic valves they used on Alicia.
http://img504.imageshack.us/img504/6606/4smix6.jpg
http://img504.imageshack.us/img504/1405/6smxt9.jpg
http://img504.imageshack.us/img504/7451/bottleracklargefy9.jpg
http://www.habonim.com/home/index.html
They I believe are controlled electronicly, but I'm not sure exactly how. I would venture to guess they are using a basic electric switch to control solenoid valves, that control the compressed air, with manual valves for back-up in the stern of the sub.
"4. What is the typical way of actuating bow and stern control
planes?"
Manual and/or hydraulic.
Best Regards,
Brent Hartwig
From: "Lil Brother LLC" <lil_brother_llc@bellsouth.net>
Reply-To: personal_submersibles@psubs.org
To: <personal_submersibles@psubs.org>
Subject: [PSUBS-MAILIST] Some thoughts on construction (I'm new so my research is not that thorough)
Date: Fri, 20 Jul 2007 17:05:24 -0500
>First I would like to thank everyone for a warm welcome. It is nice
>to see a group of people that openly accepts the new guy to the
>group.
>
>I have a question or two that can be broken up into various
>departments:
>
>1. If the ballast tanks were to totally surround the crew
>compartment, could the ballast area be used structurally?
>
> I mean if the air were purged, then the ballast area totally
>sealed (with valves). Would this enhance the structure to help with
>the pressure at depth?
>
> I figure since this area would be totally filled with water
>(which doesn't compress easily) it would add pressure resistance of
>the hull. (I'm only guessing at this......so anyone could point out
>the error in my view)
>
> I know totally encapsulating( mostly.....the top hatch could
>never be totally surrounded) the crew compartment within a ballast
>area would be a major pain, and would be hard to up keep over a long
> period of time, but it may be worth the while if the design is
>possible.
>
>2. I've noticed a very strange item on the X300( nice fiberglass
>single place, dolphin shaped sub) aft end. I'm very curious what the
>item is. I would also like to know what type of propulsion the sub
>uses.
>
>3. Are there any electronic valves out there that are pressure rated
>for our uses. I would like some companies to checkout to see if I
>can use them for ballast control.
>
>4. What is the typical way of actuating bow and stern control
>planes?
>
>Any other things you would like to point out.....would be
>appreciated. I do not have any materials to read regarding the
>design and construction of a sub. My area is very rural and the
>library is much to be desired.
>
>
>James Long
>Owner/Designer
>Lil Brother LLC (Instrument Division)
>
>
>
>
>
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