[PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
jimtoddpsub at aol.com
jimtoddpsub at aol.com
Sun Jan 12 14:26:28 EST 2014
Joe, Hank, et al,
The preliminary size for the fore/aft VBTs is 12 liters each or 26 lb of buoyancy each. One reason for this is if I pick up a load with the arm, I can compensate for the load to that extent. On the other hand I could plumb for VBTs but not install them until I've done some test dives and see how it goes without VBTs. The tanks could end up being smaller, and they don't have to both be the same size.
Lead is about 11 times the density of sea water, so it doesn't take up nearly as much room.
Jim
-----Original Message-----
From: Joe Perkel <josephperkel at yahoo.com>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sun, Jan 12, 2014 1:05 pm
Subject: Re: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Hank,
I'm looking over a variation of something Jim said for solo compensation.
Picture James Frankland's boat with the floorboard in section. Assuming at least a 3 - 4" space, either a water tank/bladder or soft weight belts/bags handed down the hatch does the trick nicely.
Alvin Jr. is going to have external ribs and a single centerline battery box. This space under the floor-board at 4" x 72" yields 4500 Cubic inches. The sub will also have two dedicated infinitely variable vertical thrusters.
Vance's comments about mass drives home Alec's previous comments about the VBT and make sense to me now. I'm going to ixnay the VBT in favor of a closely monitored weight and fine vertical thrust profile.
Joe
From: hank pronk <hanker_20032000 at yahoo.ca>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sunday, January 12, 2014 11:57 AM
Subject: Re: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Joe,
My little yellow sub has a 3 litre vbt and it worked perfect in the test pool. that is all you need for getting it perfect. When I did my life support test in the pool, I had it neutral for at least 15 min. that is according to my friend that was monitoring and recording everything. I couldn't really tell because I had no reference, I just took directions. I would design for a small tank just in case you find you need it.
Hank
On Sunday, January 12, 2014 9:33:37 AM, Joe Perkel <josephperkel at yahoo.com> wrote:
Vance,
I hear you Jim, and Alec on this issue. In order to get that 10% margin or even just to break even the volume gets too big for the size of boat.
However, having zero sub pilot experience I do have plenty of experience with a buoyancy compensator for sport diving. Several minute adjustments have to be made during a typical dive to keep from either continuously having to kick to keep down, or keep from bumping into the bottom or whatever.
How do the Nektons do it? Is it a matter of constant forward motion on the dive plane?
I want to be able to hover (hold station) in a stable manner over a fixed spot for photography, isn't very fine buoyancy control a must then?
Joe
From: "vbra676539 at aol.com" <vbra676539 at aol.com>
To: personal_submersibles at psubs.org
Sent: Sunday, January 12, 2014 10:11 AM
Subject: Re: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Hank and all,
VBTs are nice if you have the room and the need. All those dives with the Nektons prove you can get along without. And in shallow water, we usually ran the Perry boats a little heavy and then hung on a small bubble in the MBTs. Aquarius has a third MBT (soft tank), a small one up forward, that they use to tweak for neutral after diving negative. Not hard tanks. It definitely works okay. The K-boats have VBTs, but George Kittredge came from the twenty-five hundred tons displacement school of thought.
For us, it's pretty easy just to adjust a little as we go along. Mind you, my 350 has a VBT and I'm keeping it. We did a lot of mid-water work with the JSLs, and the pilots could trim 14-tons dead nuts neutral and then just forget about it. Just so you know, the JSL variable tanks and control systems, et al, probably weigh a thousand pounds in air. Fiberglas tanks and pumps and all the rest in a Perry--probably three-hundred or thereabouts.
On the little-bitty side, the Deepworkers have a simple external tank for surface work, which could certainly be used for variable ballast, but mostly aren't. Keep in mind, that is their ONLY ballast system aside from pre-dive adjustments with lead. Regardless, and aside from the general complexity, VBT systems impose a pretty hefty weight penalty on (in our case) very lightweight boats. Just something to think about.
Vance
-----Original Message-----
From: hank pronk <hanker_20032000 at yahoo.ca>
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>
Sent: Sun, Jan 12, 2014 9:39 am
Subject: Re: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Jim, Joe,
When I test Gamma next month or when the weather improves, I intend to use a ballast bag that holds 350 lbs of water. I will place it where the passenger is normally. There is the benefit of less draft on launch and less weight to haul for 12 hr of driving. I will not need to screw with weights in and out. I bought the ballast bags for other reasons and think they might be the answer. Gamma was built with a trim tank that was removed, so I want to put some dives on it before I decide if I need it. Like Vance says firmly, you don't need a vbt. In an effort to keep it simple, I will try it without.
Hank
On Sunday, January 12, 2014 7:27:35 AM, "jimtoddpsub at aol.com" <jimtoddpsub at aol.com> wrote:
Hi Joe,
I tried hard to come up with a VBT system to greatly reduce the need to load or unload lead to adjust or compensate for passenger/no-passenger and the variability in the weight of the pilot or passenger. That would have meant adding 25-30 gallons of VBT capacity to whatever VBT capacity was already planned. It also meant that VBT would have to be located at the same position fore/aft as the passenger. Picture in your mind the size of a 30-gallon drum. Whether the VBT was internal or external it was very apparent that it just wasn't workable.
Adding/subtracting lead externally isn't so hard when the sub is on the trailer, but it's difficult when the sub is in the water. In the end the simplest, most convenient system came right back to +/- lead directly under the pilot's and passenger's seats. The only practical alternative I've seen so far for a very small sub is Alec's arrangement for adding or subtracting trawler floats to adjust buoyancy.
I have two external VBTs - one fore, one aft, so they can be used for trim as well as overall buoyancy. The capacity of each is not yet determined. The forward one can be used to compensate for the addition of equipment up to a point.
Best regards,
Jim
-----Original Message-----
From: Joe Perkel <josephperkel at yahoo.com>
To: personal_submersibles <personal_submersibles at psubs.org>
Sent: Sun, Jan 12, 2014 6:18 am
Subject: Re: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Alan,
I've been giving this issue of fine buoyancy control some thought lately. In the literature is there any mention of a rule of thumb volume to vehicle ratio for the capacity?
On a K-350, the difference between diving solo or with a passenger could be as much as 200 lbs (100 kg). I would think that it would be convenient and useful to be able to compensate for this without having to manually transfer solid ballast (lead). The standard VBT volume is too small to be able to do so.
Joe
Sent from Yahoo Mail for iPad
From: Alan <alanlindsayjames at yahoo.com>;
To: Personal Submersibles General Discussion <personal_submersibles at psubs.org>;
Subject: Re: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Sent: Sun, Jan 12, 2014 9:20:37 AM
Hi jim,
here's a G.L. quote. "Normally compensating tanks are to be provided for a fine
adjustment of the wanted depth and for balancing of changes of buoyancy
because of consumption of provisions & supplies during the underwater voyage,
changes of the density of seawater, taking on or taking off of payloads as well
as effects of buoyancy/loss of buoyancy."
This section covers hard & soft tanks, internal & external, & calls them all
compensating tanks.
Alan
Sent from my iPad
On 12/01/2014, at 9:59 am, jimtoddpsub at aol.com wrote:
Hi Alan,
Thanks for posting that. What all does "compensating tanks" refer to?
Best regards,
Jim
-----Original Message-----
From: Alan James <alanlindsayjames at yahoo.com>
To: psubs.org <personal_submersibles at psubs.org>
Sent: Fri, Jan 10, 2014 5:37 pm
Subject: [PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming
Hi all,
This is my G.L. summary of Diving/Ballasting, Control/Compensating & Trimming.
It builds a little on a previous section "Stability & buoyancy".
All the ballasting controls & systems have to work under previously specified heel & trim requirements. Including when one main ballast tank is damaged.
It has to be possible to check these systems prior to diving.
The sub must be able to surface after the failure of a compensating tank.
Flooding & bilge openings are to be protected with grids, filters or strum boxes to stop the entrance of foreign matter.
All the operating units for controlling positive & negative buoyancy are to be grouped together & clearly marked on the control consul. This control consul is to have indicating instruments showing depth & trim.
Separate shut off valves are required for each ballast tank.
The vent valves are to be designed in such a way as to prevent unintentional opening.
Where diving tanks have flooding holes without means of closure, double shut-off
valves "May" be stipulated for the vent pipe.
The blowing line for each tank has to have a separate shut off.
Blowing the tanks cannot cause an excessive over-pressure.
Where the diving tanks are pumped out there needs to be a closure valve & back up bilge pump. No excess under-pressure can be caused.
Compensating tanks are to be designed big enough for all the changes in
buoyancy plus 10%
Compensating tanks need contents gauges to give continuous readings.
The compensating tank vent pipes need to be wide enough for maximum
inflow / outflow and designed so that water can't flow from them unnoticed in to the hull.
The volume of the trimming tanks is designed in such a way that all planned trimming situations can be adjusted by combined filling & emptying of the various tanks.
Alan
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