[PSUBS-MAILIST] G.L. rules Arrangement for Diving/Ballasting, Control/Compensating & Trimming

Sun Jan 12 09:27:10 EST 2014

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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