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Re: [PSUBS-MAILIST] hard ballast

3 tons!!! Yikes.

Pitch control is something else. They used to do it with mercury in fore and aft tanks. Not a nice material to work with, and expensive. It depends on whether the sub needs that. Will you have control surfaces? Maneuvering thrusters? If you intend to use the hull pitch for maneuvering underway, then yes, it would be necessary. If not, then just shoving lead around can do the trick.

Captain K did a nice little design with a 5' ball as a 2-man pressure hull and a single battery pod stuck out the back. The pod had a rail system underneath with a weight skid that could be run fore and aft by hand (a long screw with a penetrator at the back of the hull. With a design like that, you'd need to do something like that, especially to offset anything retrieved with your crane off the bottom.

For a long hull that is already adequately maneuverable, I'd probably not add the weight or complexity, but that's just me. That's the thing about psubs. I mean, look at Frank. He's building a plump kind of shark!!! How cool is that?

Vance


-----Original Message-----
From: Brian Cox <ojaivalleybeefarm@dslextreme.com>
To: personal_submersibles@psubs.org
Sent: Thu, 5 Feb 2009 10:14 am
Subject: RE: [PSUBS-MAILIST] hard ballast

My pressure hull is small but my soft ballast is hugh !   My ballast structure is going to come in at around 3 tons ( on land wieght) .  I have an area where everything has to go, so I can't just add stuff onto the outside. ( and I keep thinking of more things to add !!  ( cranes, anchors, manip arms etc..)  )   Sounds like not a good idea to put VBT inside.    I may do a sliding lead weight on a rail on the keel for trim .
 
Brian
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of vbra676539@aol.com
Sent: Thursday, February 05, 2009 7:50 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] hard ballast

Let me qualify that. Assuming stable depth and minor quantities of air, the sub will do what you want it to do, but slowly. There is some finesse to it, of course. However, a PC12, for instance, weighs approximately 8 tons, and a squirt of air might be just a few pounds difference in its trim. It WILL make a difference, just not a massive one (unless you want it to). That same squirt of air in a 3300 pound K-350 will make a much more immediate difference, with longer lasting effects. In other words, caution is advised, as the Captain's finest will respond MUCH faster than the PC12, simply because it weighs so much less.

That said, I'm not advocating you toss out your trim system. My question was aimed more at design. A 32" pressure hull is SMALL. So why stick a spherical tank into such a small space, unless it can be made to serve some other purpose. For instance, the DW2000s are built to sit in, so the internal soft tank is under the seat. In other words, it isn't in the way.

Vance


-----Original Message-----
From: vbra676539@aol.com
To: personal_submersibles@psubs.org
Sent: Thu, 5 Feb 2009 9:31 am
Subject: Re: [PSUBS-MAILIST] hard ballast

Pretty much.
V


-----Original Message-----
From: Brian Cox <ojaivalleybeefarm@dslextreme.com>
To: personal_submersibles@psubs.org
Sent: Thu, 5 Feb 2009 6:57 am
Subject: RE: [PSUBS-MAILIST] hard ballast

So you're saying that the mass of the boat is is so much that the change in the amount of air in the soft ballast takes a long time to affect the buoyancy ?  Except it's more pronounced in shallow water.
 
Brian
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of vbra676539@aol.com
Sent: Thursday, February 05, 2009 4:30 AM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] hard ballast

Simply put, there is enough mass there to work without a vbt system, so why bother.

What difference does the space make outside the boat?

V


-----Original Message-----
From: Brian Cox <ojaivalleybeefarm@dslextreme.com>
To: personal_submersibles@psubs.org
Sent: Wed, 4 Feb 2009 8:02 pm
Subject: RE: [PSUBS-MAILIST] hard ballast

The reason I'm contemplating it is to save space.  It would be a sphere and if I put it outside in front of my 32" dia pressure hull then I will have the end cap of the pressure hull butting up against the hard ballast sphere so there would be this area where the two spheres come together that would be wasted. 
 
Vance,   Does the Aquarius not have hard ballast tanks?   Sorry if you already be thru this.
 
Brian
-----Original Message-----
From: owner-personal_submersibles@psubs.org [mailto:owner-personal_submersibles@psubs.org]On Behalf Of vbra676539@aol.com
Sent: Wednesday, February 04, 2009 4:44 PM
To: personal_submersibles@psubs.org
Subject: Re: [PSUBS-MAILIST] hard ballast

They probably did not replace the VBT. You just dive a little heavy and ride the bubble. There has been lots of talk here about that, but I'm here to tell you, it works just fine. Aquarius hasn't had a trim system since about 1975, and is working its little buns off all year, every year. You trim the boat carefully during pre-dive, and then you don't need much extra buoyancy. The real issue is in shallow water where that bubble can and does expand rapidly. But if you think about nearly any partially flooded ambient sub on the planet, guess what it uses as primary buoyancy. A bubble. It works just fine. Trust me.
Vance


-----Original Message-----
From: Brent Hartwig <brenthartwig@hotmail.com>
To: PSUBSorg <personal_submersibles@psubs.org>
Sent: Wed, 4 Feb 2009 6:01 pm
Subject: RE: [PSUBS-MAILIST] hard ballast



Brian, I meant to say the K-250 boats generally have short VBT just under the pilots seat, inside.  But some like the Great White K-250 have removed them so they can have two people inside.  I still don't know exactly what they replaced it with.  I'll have to ask Greg Cottrell, or Scott Cassell.


Szybowski




From: brenthartwig@hotmail.com
To: personal_submersibles@psubs.org
Subject: RE: [PSUBS-MAILIST] hard ballast
Date: Wed, 4 Feb 2009 15:52:29 -0800


Hi Brian,  The K boats generally have a short VBT just under the pilots seat. You might also consider using a bladder type that you can let water into with a valve, and then either just dump it out when at the surface, or better yet have a high pressure electric pump that can empty it for you at depth.  Another version of this is a box tank, like was used in the S101 that you operate just like the bladder with a pump. The box tank can not take internal or external pressure, it is just a holding tank.   Here is a drawing of the S101. The holding tank is just behind the conning tower, and taking up the lower half of the hull.

http://www.msubs.com/Images/S101%20Images/S101%20-%206.jpg


Szybowski




From: ojaivalleybeefarm@dslextreme.com
To: personal_submersibles@psubs.org
Subject: [PSUBS-MAILIST] hard ballast
Date: Wed, 4 Feb 2009 14:43:01 -0800

Hi All,
            I'm contemplating puting a hard ballast tank inside my pressure hull.  Do any of the Kittridge subs have this same set up ?
 
Brian
 
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