[PSUBS-MAILIST] Personal_Submersibles Digest, Vol 120, Issue 40

Wed Aug 16 23:58:34 EDT 2023

I think I may have offered this the last time the VBT discussion came up, but I always thought that a good control scheme for the VBT would be to automate it within a slave loop to the vertical thruster control. So, for example, you have a position setpoint in the vertical direction which is either auto-depth or auto-altitude, and have your vertical thrusters programmed to respond accordingly to maintain that setpoint. Separately, you monitor the instantaneous output to the vertical thrusters that results from that control loop, filtered on a longer time base, and operate one of two valves via a slower acting control loop to either admit water to the VBT, or open the pump discharge to let water out, as necessary in order to null out that thruster input. This way, external disturbances such as vertical currents, or buoyancy changes due to hull deflection at depth etc., would be compensated for automatically, and the system would also act to conserve energy by minimizing power consumption to the vertical thrusters, by always dialing the boat to neutral.

When not holding an altitude or depth, the system could also activate whenever the manual thruster command was saturated at 100% in either direction, in order to hasten a long ascent or descent, or possibly to respond to the condition where the available vertical thrust is insufficient. The only caveat would be to make sure that you don't allow so much VBT volume that you couldn't manually counter the resultant buoyant force with opposing thrust in an emergency.

Such an embodiment would require a check valve based reciprocating pump, like a Sprague, that could be deadheaded against the discharge valve at full outlet pressure. Opening the discharge valve would cause it to stroke, while closing the discharge valve would deadhead it again. This is possibly a safety feature, because as as long as the pump is not stroking with the discharge valve closed, you know it can develop pressure, and again, having a pump that just stops when pressure builds downstream will conserve the HP air or electrical power used to drive it, in contrast to a pump that must be explicitly run.

Just a thought.

Sean

-------- Original Message --------
On Aug. 16, 2023, 21:18, Cliff Redus via Personal_Submersibles wrote:

> Hugh, I understand the attraction of using VBT for QSub. With a mission profile to be able to do long ocean surface transects to a dive location, submerge, dive, surface and then transect back. It is not practical to haul excess ballast since the Qsub is operating more like a submarine than a submersible. If you can find a positive displacement pump that does not have a lot of slippage at your maximum depth, then the issue I mentioned about opening the VBT at depth and getting negatively buoyant goes away because the pump itself is preventing a large inrush of water. When this happened on my boat, I had already switched to air for blowing VBT. I would, as you note, adjust the water in the VBT just below the surface after flooding the MBTs. This was the NOP but sometimes the unexpected happens and you need to add buoyancy at depth with the VBT. I was diving the R300 about seven years ago at Lake Amistad on the border between Mexico and Texas. I submerged to about 150 ft in old river bottom. When I lifted of the bottom to start the ascent using my vertical thrusters at an altitude of about 10ft, the boat stopped ascending even with full vertical thrusters. I was watching the depth gage and I was just going up. I did not realize it but I was being dragged along by a 5-knot current and was not accenting at a rate I was comfortable with. The boat at the time was neutrally buoyant. To increase the rate of ascent, I decided to blow the VBT at depth. The depth was about 140 ft at the time. When I opened the motorized ball valve on the vent side of the VBT, the boat started descending even though air was being introduced because of this sudden influx of water. Eventually, the water in the VBT was displaced with air and the boat started to ascend. When I surfaced, I was about a mile downstream from the tender vessel. Because the water visibly was so bad, I did not realize I was being dragged by the current so much.
>
> Cliff
>
> On Wednesday, August 16, 2023 at 09:25:55 PM CDT, via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Hi Cliff,
> I am interested in your comments re the pump slippage etc and operation of
> the VBTs when you were using them.
> My approach, untried and purely theoretical, was that most of the VBT
> adjustment would be done just below the surface and only minor adjustment
> for compression of vessels etc would be done at depth.
> I do appreciate that weight balance appears more foolproof. Regards, Hugh
>
> -----Original Message-----
> From: Personal_Submersibles <personal_submersibles-bounces at psubs.org> On
> Behalf Of via Personal_Submersibles
> Sent: Thursday, August 17, 2023 1:02 PM
> To: personal_submersibles at psubs.org
> Subject: Personal_Submersibles Digest, Vol 120, Issue 40
>
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> 1. Re: Re VBT Pump (Cliff Redus via Personal_Submersibles)
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Thu, 17 Aug 2023 01:01:56 +0000 (UTC)
> From: Cliff Redus via Personal_Submersibles
> <personal_submersibles at psubs.org>
> To: via Personal_Submersibles <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] Re VBT Pump
> Message-ID: <2137621386.758356.1692234116222 at mail.yahoo.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hugh, thanks for update on QSub.? I am looking forward to her dunk test in
> your new test pool. I quite enjoyed sitting in her pressure hull in your
> shop in New Zealand a few years back.? She will be quite something when
> complete.
> Best
> On Wednesday, August 16, 2023 at 06:43:41 PM CDT, via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:
>
> Thanks, Cliff, Alec, Vance, Jon.
>
> The model I was looking at, correction, was the Oberdorfer 994 which is same
> as a 2000 series but 3/8" - 1/2"? and direct mounted not foot mounted as per
> the 2000 series.
>
> The other pump I liked was the Wanner D10 which is diaphragm and can do no
> slippage and 250 -300 psi etc but it is not bidirectional.? However that can
> be fixed with valves.
>
> I am making some progress with my Q-Sub but made the mistake of going too
> complex and trying to do everything.? I? have had issues with --- 1. BMS
> systems for the LiFePO4 batteries and had to replace these.
> 2. Precharge systems for the 72 v and 144 volt electrics and voltage spikes.
> 3. Gear cable kinking for the mercruiser sternlegs.
> 4. Inaccessible fuses and not motor rated.
> 5. Mechanical seal leakage on the hydraulics.
> 6. Joystick pot issues.
> 7. Canbus systems at different voltages.
> 8. Rotary sensors too coarse required op amp addition to amplify signals for
> small rotary movements with steering.
> 9. Port Engine starting issues.
> 10. Oil compensation line fittings leaks.
> 11. Software issues.
>
> Still plugging along.? IN the meantime I have built a test pool same-same
> Hank 8 ft deep 12 wide x 27 long, and another gantry crane for PVHO removal,
> as well as a shed just for the sub.? This year it has to be finished.? Has
> not even been in the pool yet!!
> Regards,? Hugh
>
> -----Original Message-----
> From: Personal_Submersibles <personal_submersibles-bounces at psubs.org> On
> Behalf Of via Personal_Submersibles
> Sent: Thursday, August 17, 2023 3:21 AM
> To: personal_submersibles at psubs.org
> Subject: Personal_Submersibles Digest, Vol 120, Issue 36
>
> Send Personal_Submersibles mailing list submissions to ???
> personal_submersibles at psubs.org
>
> To subscribe or unsubscribe via the World Wide Web, visit ???
> http://www.whoweb.com/mailman/listinfo.cgi/personal_submersibles
> or, via email, send a message with subject or body 'help' to ???
> personal_submersibles-request at psubs.org
>
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> When replying, please edit your Subject line so it is more specific than
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>
> Today's Topics:
>
> ? 1. Re: FW: VBT pump (Cliff Redus via Personal_Submersibles) ? 2. Re: FW:
> VBT pump (Alec Smyth via Personal_Submersibles) ? 3. Re: FW: VBT pump (Jon
> Wallace via Personal_Submersibles)
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Wed, 16 Aug 2023 13:29:07 +0000 (UTC)
> From: Cliff Redus via Personal_Submersibles ???
> <personal_submersibles at psubs.org>
> To: via Personal_Submersibles <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] FW: VBT pump
> Message-ID: <536726240.403633.1692192547749 at mail.yahoo.com>
> Content-Type: text/plain; charset="utf-8"
>
> Hugh, on my original design for the R300 I had a hard VBT just aft of the
> pilot. At the time I had a small HPU in the boat.? My plan was to use a
> Oberdorfer Bronze gear pump driven by a small hydraulic motor to move water
> in and out of the VBT.? I don't remember the specs on the pump.? I had
> motorized ball valves on the vent and flood side of the VBT.? Prior to using
> this set up, I did some testing of this gear pump which I still have.? What
> I found was an unacceptable amount of flow slippage at my max design depth.?
> There was so much slippage that the pump could not blow the VBT at max
> depth.? At that point I abandoned using a pump and vent to blowing the VBT
> with air.? I eventually abandoned the VBT altogether for operability
> reasons.? When I used this hard VBT to get neutral on the surface, the
> pressure in the tank was low.? When at depth if I ever tried to use the VBT,
> water would rush in until the pressure equalized with ambient water
> pressure.? This made the boat nega!
> tively buoyant until air was added.? The other thing that bugged me was I
> had a float style level sensor in the VBT.? The water level in the VBT was
> always moving around so you never trust the reading.? I eventually abandoned
> the VBT and now just add ballast at the boat CG where the VBT was located.?
> I find this works great.? The other issue is the VBT restricted access to
> equipment aft of the VBT so to work on any of this equipment, I had to
> remove the VBT.? ?All in all, I found the VBT to be a pain in butt.
> Cliff
> Oberdorfer 944 Bronze
>
> ? ? On Sunday, August 13, 2023 at 04:57:24 PM CDT, via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:?
>
> Hi Guys
>
> ?
>
> What make of pump is best for VBT water transfer in/out for 250 psi 1.5 kw.
>
> I am looking at a gear pump 1.5kw Oberdorfer 944 Bronze.? These are only
> rated for 10 bar.? I tried an hydraulic gear pump 30cc where I had a
> stainless and bronze gear set made up but the aluminium body corroded form
> the trials and I just found that they had used steel backed sleeve bearings.
>
> ?
>
> Regards,
>
> Hugh
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
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> Message: 2
> Date: Wed, 16 Aug 2023 09:41:53 -0400
> From: Alec Smyth via Personal_Submersibles ???
> <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion ???
> <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] FW: VBT pump
> Message-ID:
> ??? <CABECYQ7JnW3k0Jz+wtvG64tx4pApp=vj5vkF9yWW2NN0fQMU3Q at mail.gmail.com>
> Content-Type: text/plain; charset="utf-8"
>
> I second that (getting rid of VBT). I got rid of the VBT in my K250 years
> ago to make space and turn it into a 2-person and to try and to simplify,
> and it worked so well I never thought of using any other method on the
> current sub. The only difference with Cliff's method is that I add or remove
> floats, while he uses ballast. But either way, once you have a reference
> point for how much ballast/buoyancy you need for a given crew weight, you
> just make incremental changes and it never fails. You may be off neutral by
> just a few pounds, but if you have vertical thrusters they're usually just
> ticking over at slow RPMs to compensate.
>
> Best,
> Alec
>
> On Wed, Aug 16, 2023 at 9:30?AM Cliff Redus via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
>> Hugh, on my original design for the R300 I had a hard VBT just aft of
>> the pilot. At the time I had a small HPU in the boat.? My plan was to
>> use a Oberdorfer Bronze gear pump driven by a small hydraulic motor to
>> move water in and out of the VBT.? I don't remember the specs on the
>> pump.? I had motorized ball valves on the vent and flood side of the
>> VBT.? Prior to using this set up, I did some testing of this gear pump
>> which I still have.? What I found was an unacceptable amount of flow
>> slippage at my max design depth.? There was so much slippage that the
>> pump could not blow the VBT at max depth.? At that point I abandoned
>> using a pump and vent to blowing the VBT with air.? I eventually
>> abandoned the VBT altogether for operability reasons.? When I used
>> this hard VBT to get neutral on the surface, the pressure in the tank
>> was low.? When at depth if I ever tried to use the VBT, water would
>> rush in until the pressure equalized with ambient water pressure.?
>> This made the boat negatively buoyant until air was added.? The other
>> thing that bugged me was I had a float style level sensor in the VBT.?
>> The water level in the VBT was always moving around so you never trust
>> the reading.? I eventually abandoned the VBT and now just add ballast
>> at the boat CG where the VBT was located.? I find this works great.?
>> The
> other issue is the VBT restricted access to equipment aft of
>> the VBT so to work on any of this equipment, I had to remove the VBT.
> All
>> in all, I found the VBT to be a pain in butt.
>>
>> Cliff
>>
>> Oberdorfer 944 Bronze
>>
>> On Sunday, August 13, 2023 at 04:57:24 PM CDT, via
>> Personal_Submersibles < personal_submersibles at psubs.org> wrote:
>>
>>
>> Hi Guys
>>
>>
>>
>> What make of pump is best for VBT water transfer in/out for 250 psi
>> 1.5
> kw.
>>
>> I am looking at a gear pump 1.5kw Oberdorfer 944 Bronze.? These are
>> only rated for 10 bar.? I tried an hydraulic gear pump 30cc where I
>> had a stainless and bronze gear set made up but the aluminium body
>> corroded form the trials and I just found that they had used steel
>> backed
> sleeve bearings.
>>
>>
>>
>> Regards,
>>
>> Hugh
>> _______________________________________________
>> Personal_Submersibles mailing list
>> Personal_Submersibles at psubs.org
>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>> _______________________________________________
>> Personal_Submersibles mailing list
>> Personal_Submersibles at psubs.org
>> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>>
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> Message: 3
> Date: Wed, 16 Aug 2023 15:20:44 +0000 (UTC)
> From: Jon Wallace via Personal_Submersibles ???
> <personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion ???
> <personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] FW: VBT pump
> Message-ID: <1959084270.469930.1692199244774 at mail.yahoo.com>
> Content-Type: text/plain; charset="utf-8"
>
> I'll chime in here...I removed the VBT from the K600 because it was fairly
> well rusted inside and needed to be replaced, however I am planning on using
> the ballast/float method instead and forgoing the VBT altogether for many of
> the reasons Alec and Cliff cited.? I will say that it can be challenging to
> change ballast on-station since the weight/floatation has to be transferred
> somewhere and by somebody, however I see the K600 being trimmed for specific
> missions prior to launch and not being trimmed dynamically on-station to
> embark/disembark passengers or equipment.
> Jon
>
> ? ? On Wednesday, August 16, 2023 at 09:43:35 AM EDT, Alec Smyth via
> Personal_Submersibles <personal_submersibles at psubs.org> wrote:?
>
> I second that (getting rid of VBT). I got rid of the VBT in my K250 years
> ago to make space and turn it into a 2-person and to try and to
> simplify,?and it worked so well I never thought of using?any other method on
> the current sub. The only difference with Cliff's method is that I add or
> remove floats, while he uses ballast. But either way, once you have a
> reference point for how much ballast/buoyancy you need for a given crew
> weight, you just make incremental changes and it never fails. You may be off
> neutral by just a few pounds, but if you have vertical thrusters they're
> usually just ticking over at slow RPMs to compensate.
>
> Best,Alec
> On Wed, Aug 16, 2023 at 9:30?AM Cliff Redus via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:
>
> Hugh, on my original design for the R300 I had a hard VBT just aft of the
> pilot. At the time I had a small HPU in the boat.? My plan was to use a
> Oberdorfer Bronze gear pump driven by a small hydraulic motor to move water
> in and out of the VBT.? I don't remember the specs on the pump.? I had
> motorized ball valves on the vent and flood side of the VBT.? Prior to using
> this set up, I did some testing of this gear pump which I still have.? What
> I found was an unacceptable amount of flow slippage at my max design depth.?
> There was so much slippage that the pump could not blow the VBT at max
> depth.? At that point I abandoned using a pump and vent to blowing the VBT
> with air.? I eventually abandoned the VBT altogether for operability
> reasons.? When I used this hard VBT to get neutral on the surface, the
> pressure in the tank was low.? When at depth if I ever tried to use the VBT,
> water would rush in until the pressure equalized with ambient water
> pressure.? This made the boat nega!
> tively buoyant until air was added.? The other thing that bugged me was I
> had a float style level sensor in the VBT.? The water level in the VBT was
> always moving around so you never trust the reading.? I eventually abandoned
> the VBT and now just add ballast at the boat CG where the VBT was located.?
> I find this works great.? The other issue is the VBT restricted access to
> equipment aft of the VBT so to work on any of this equipment, I had to
> remove the VBT.? ?All in all, I found the VBT to be a pain in butt.
> Cliff
> Oberdorfer 944 Bronze
>
> ? ? On Sunday, August 13, 2023 at 04:57:24 PM CDT, via Personal_Submersibles
> <personal_submersibles at psubs.org> wrote:?
>
> Hi Guys
>
> ?
>
> What make of pump is best for VBT water transfer in/out for 250 psi 1.5 kw.
>
> I am looking at a gear pump 1.5kw Oberdorfer 944 Bronze.? These are only
> rated for 10 bar.? I tried an hydraulic gear pump 30cc where I had a
> stainless and bronze gear set made up but the aluminium body corroded form
> the trials and I just found that they had used steel backed sleeve bearings.
>
> ?
>
> Regards,
>
> Hugh
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
> ? _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
>
> _______________________________________________
> Personal_Submersibles mailing list
> Personal_Submersibles at psubs.org
> http://www.psubs.org/mailman/listinfo.cgi/personal_submersibles
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