[PSUBS-MAILIST] Vanguard class sub (UK) unintended depth excursion

Tue Nov 21 09:22:31 EST 2023

 The O2 and CO2 electronic sensors I use can be calibrated in open air.  Of course that requires that the sensors can be removed from the vessel and taken to an open area, which mine can.  In situ, you'd have to use a test gas of known purity which would be another tank to drag around.  Pressure transducer testing could be done with just a scuba tank as the supply gas.
If a vessel is diving in water shallower than it's rated depth would a pressure transducer verification still be critical?
Jon

    On Tuesday, November 21, 2023 at 08:29:05 AM EST, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 I wasn't thinking of verification at depth, but rather verification of the transducer(s) / gauges prior to the dive, as distinct from a full calibration.

Having, for example, a process connection on the vessel that would allow you to tie in a pressure source and a reference gauge, and doing a quick two-point verification of the gauge readings at 20% and 80% of nominal range - all before getting wet.

Incidentally, here is the ABS language on the subject. It seems that redundant systems are 

"
13.3 Monitoring Equipment (2007) Life support instrumentation systems, including power supplies, are to be provided in duplicate or an alternative means of measurement is to be provided. Changes in temperature, humidity and total pressure are not to affect the accuracy of measurements. Electronic life support instrumentation is to incorporate provisions for calibration. Internal pressure is to be monitored using a mechanical type instrument in addition to any other type of pressure indicating instrument.
"

Sean
-------- Original Message --------
On Nov. 21, 2023, 06:00, Al Secor via Personal_Submersibles < personal_submersibles at psubs.org> wrote:

That would only add the danger of entanglement.  I would add a pressure gauge (analog) in series of the digital sensoror scuba depth gauge mounted outside in view of the pilot.
Al

On Tue, Nov 21, 2023 at 7:24 AM Jon Wallace via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 As Dan mentioned, for psubbers, not diving in water deeper than your sub's capability is good advice and we have this concept codified in the PSUBS operating guidelines section 4.1.2 paragraph 2.  Using multiple sensors for either backup or a weighted result between them is also a good idea except could be an expensive option given the price of some sensors.  A pressure transducer of mediocre accuracy for example is going to be in the $150 each range.
What kind of protocol for verification of a single sensor would be effective?  The only thing I can think of for depth would be tying a marked rope to the vessel and comparing the pilot's observation to surface observation.
Jon

    On Monday, November 20, 2023 at 11:57:50 AM EST, Sean T. Stevenson via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Just read an article about an incident with a British Vanguard Class submarine that had an incident where it went far too deep, apparently as a result of faulty instrumentation. Engineers became aware of the sub's depth when they observed some backup depth instrument(s) and rectified the situation before it became a castastrophe.

Just wanted to prompt some discussion here, because PSubs don't necessarily employ robust backup systems, and at minimum, we should endeavour to ensure that all critical instrumentation is periodically calibrated to some reference standard to ensure accuracy, and also periodically verified in order to have some mechanism in place to detect malfunctioning instruments.

Backup instrumentation is a great method to achieve the latter (instrument verification), but comparing the primary and backup instruments needs to be part of SOPs. Where backups don't exist, some means of functional verification should at least be employed, if not per dive, then perhaps per trip?

This was a military sub that was almost lost because of an easily avoidable problem.

FWIW.

Sean

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