[PSUBS-MAILIST] Depth tests at Seneca

Tue Aug 31 15:11:38 EDT 2021

I thought I would put my two cents in on the Lake Seneca divesthis weekend of Shackletonand The Great Escape (TGE).  Bottom lineis both boats were successful in massively extending their operating depth to500 ft and 300 ft, respectively. This is a big milestone for each of thesepsubs and they did a great job coordinating these tests.  

 I don’t have much toadd on the dives other than the working hypothesis of the extruded O-ring onShackleton.  Another possible hypothesis isoverpressure from heating of the air in the battery pod could have caused theextrusion.  The initial pressure in the podwas ambient at the temperature of Alec’s garage in Virginia when he closed upthe pod after the initial charging. It is possible the top off charge causedsome pressure build but, in my experience, the smart charger should have beenin the third phase of charge which is high voltage, low current switching onand off.  It is hard for me see thisgenerating the kind of pressure needed to unseat the o-ring.   On thetest dive day at Lake Seneca we did not get the Shackleton into the water tillaround noon.  The temperature could easilyhave been over 100 F from the sun.  Hotair has a lower density than cold so this could have caused the overpressure inthe port pod in that the OP valve on the pod was locked out.  We had multiple people looking at the boat fromthe time we got to the lake which I think was around 9 am or so until the launcharound noon.  No one noticed the extrudedo-ring which was in a very observable location being at the top of the portbattery pod very near the bow view port. The extrusion was about 1 inch in length.  If it had been extruded at that point, then Ithink someone would have noticed this black 1 inch extruded O- ring against thewhite color of the pod.  This leads me tothink the extrusion happed sometime after the launch.  We noticed the listing on the tow out.  My guess is that the water temperature at thesurface was on the order of  65 F.  As such, when the battery pods were submergedthe air in the pods stated to cool down quickly so 1 atm air in the pod promptlydropped into a partial vacuum pulled in water. Of course, as the boat descendedto 500 ft, this extruded O-ring presented a flow path for the water and thehigh differential pressure between ambient water and pod pressure flooded thepod.   I concur with Alec in that the ABSrule that requires the boat to be able to be surfaced with MBT blow with thelargest non-hull floodable volume (in this case, one of the battery pods) beingcompletely flooded saved the day.  Alecis braver than me.  I was arguing foraborting the dive until we sorted this out.

 So the lesson learnedto me was to add a visual and tactile inspection of both battery pod joints tothe predive checklist and as Alec notes, open the wing nut on the battery podOP valve so that any overpressure event in the pod would be safely vented.

Concerning the hiccup with The Great Escape on the Friday ballastcheckout dive, in retrospect, the problem of air from deepest MBT, either forwardor aft, forcing air into the more shallow tank could have been prevented withtwo low-cracking pressure check or non return valves positioned on both branchingsides of the test rig tee.  This wouldhave prevented this longitudinal movement of air between the MBTS.  Standing on the boat watching and excessive amountof air venting from the forward and aft MBS while no air was being added was causingus all to scratch our heads.  It was Dan Lancethat picked up on the problem.  

After recovering the boat, Steve’s solution of with a quickrun to the hardware shop for another valve  solved the problem and the next days dive wentoff fine except for the extra 20 minutes we waited for the boat tosurface.  I sure thought we were going toneed our weaties to manually hall in the boat. Steve just kept saying, just give it another 5 minutes.

Dive operations with Shackleton on Monday were in jeopardy due to Alec’sback which he managed to strain holding onto the line attached to Shackleton for an hour as she sat at500ft during the unmanned depth test.  Hisonly requirement for our Sunday night celebration dinner was a simple straightback chair.  I thought we were going to haveto carry him out to the car after dinner.  Getting into Shackleton is a bit tricky even with a goodback. In the morning he had recovered to the point that he agreed to have a goat diving.

Alec agreedto take me for a dive as a passenger (big thanks) so below are my observationsfrom the dive.  First Alec did a greatjob in the predive orientation which was done in the boat.  He has a very specific instruction on how tomove this way and turn that way to get the passenger down the sail and into aprone on your stomach position facing the bow viewport.  I found the layout of switches and controlsto be intuitive and well labeled. We went through all the common systems firstincluding location of thruster breakers, BIBS system, exterior and interiorlights, surface and underwater comms, thruster operations and O2 makeup regulators.  After I was comfortable with basicoperations, he covered emergency items such as drop weight and jettisoning thrustersthat were entangled.  I think anyonegenerally familiar with basic components of a 1-atm boat would come up to speedpretty quickly with his layout of equipment and his orientation.

Over the years,Alec has done quite a bit of work on the MBT design mostly due to the design objectivesof the boat changing mid stream.  As suchit is very stable to walk on during passenger change outs.  Other than the absolutely beautiful view fromthe bow viewport, what I was very impressed with was the operation of the MBTpneumatic vent valves.  They are fast! Inreviewing the video of the dive with his son Treavor as passenger, it took 12seconds from when the MBT valves opened until the boat was fully flooded.  This transition period from fully blown MBTto fully flooded MBT can be problematic for some boats.  Thanks to Hugh Fulton for sharing the originaldesign of these MBT vent valves.  I lovethese valves and plan to use them on my next boat. 

Of courseSteve McQueen get bragging rights for the best Eye Candy.  TGE is just a beautiful K-250 build.  If you are wanting to fast track getting inthe water with your very own boat, Steve has put TGE on the market.  I don’t think you can find a better builtK-250.

One last point.  Steve DeMartino and James Eddlestone were twolocal experienced divers that answered our call for diving assistance duringthe trip.  They both did and outstandingjob.  Steve even opened up his lake housefor us to use as a base of operation during the trip.  He also used his boat as tender during the dives.  Steve did and excellent job in just about whateverwe asked him to do in the water including acting a counter balance on the towback with Shackleton.

It is niceto see these two boat reach a fully qualified status.

Cliff

    On Monday, August 30, 2021, 04:17:57 PM CDT, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:  

 Hi Friends,
Steve McQueen and I just depth tested our subs in Seneca Lake, and I thought I'd send a little writeup. But first, many thanks to Cliff Redus and Dan Lance for crewing! 
We prepared our subs by installing temporary MBT plumbing outside, with valves that could be operated by swimmers. The subs were to be sent down on an anchor line, and would blow tanks an hour later automatically. The "auto-pilot" that blows ballast uses a timer, but will also blow ballast ahead of time if a water detector senses a leak. 
Both tests were successful, but both were also a little too exciting. 
In my case, Shackleton developed a 45 degree list during the tow out to the test site. I was pretty certain it was a flooded battery pod, and could see the cabin was dry by looking into the bow dome, so decided to go ahead and send her down because, even though a flooded pod is a lot of extra weight, the pods are sized not to result in negative buoyancy when flooded. That is an ABS rule. The sub did indeed come back up after an hour, with the cabin still dry. 
Once back on land, we found the source of the battery pod leak had been owner stupidity (surprise!!!) I normally open the pods for charging, but in this instance had thought it unnecessary because the charging was just a really small top-up. Wrong... battery off-gassing had dislodged a pod cap O-ring. On top of that, my pods have over-pressure valves that would have avoided the issue, except that I'd bolted them as an extra security measure to prevent a leak path on the test. After all, I don't think anyone else has put OP valves on their pods so reached the conclusion they weren't necessary. Well, lessons learned. Moving forward, caps will be coming off during any charging, and the OP valves will go back into operation too (e.g. to prevent against heat expansion.) The good news is that the flood does not appear to have affected the batteries, which are AGMs. We dove the sub the next day. All worked perfectly and the battery voltage had not decreased in the slightest.
Steve's sub, The Great Escape, had a minor issue involving the temporary MBT plumbing. Steve had plumbed both MBTs together, to a T, and put a ball valve on that. What happened was a siphon effect between the two tanks. Whichever MBT was slightly lower in the water would transfer air to the higher one, from which it would escape. Steve redid the temporary plumbing, putting a separate ball valve on each tank, and the issue was fixed. His test went well, except he was conservative turning the knob on the timer, so the autopilot went off about 20 minutes later than planned - and he probably aged 20 years in those 20 minutes. 
Seneca Lake is 600 feet deep, and the bottom is very fine silt that's another 600 feet deep and has been deposited since the last ice age. We were concerned about the subs diving into that silt and getting stuck by suction, so we held them off the bottom. One interesting thing is we could see the subs on the boat's fish-finder. Really big fish, at 500 in the first test and 300 feet in the second. 
Here was our M.O.:
1) Trim out buoyancy at the ramp so the sub will be neutrally buoyant with MBTs flooded. Set the auto-pilot timer, seal the hatch.2) Tow to test site.3) Swimmers flood MBTs and make sure to close the valves before the sub disappears.4) Add some ballast for modest negative buoyancy. Enough to prevent the sub from floating on a thermocline, but not so much you could not pull her up.5) Let sub down a little, check for leaks by looking through the view ports. We marked the rope with labeled heat shrink, at 50 foot increments. We used a rope that was longer than the depth of the lake. It had a trawl float 20 feet from the sub, to keep it clear from the valve handles, and another float on the end in case we had to let it go. The rope was not tied off on the boat, we just put a turn on a cleat and kept a hand on it. An imploding sub could sink the surface boat. 6) Wait, tracking time on a timer that was set at the same time as the one in the sub.7) The angle of the line indicates where the sub is. Ensure the surface boat is not directly above when the sub surfaces.
If anyone wants to borrow the auto-pilot for a depth test, just let me know. I think we've used it for testing about 4 subs by now. 
I'll post some photos and video on FB...

Best,
Alec_______________________________________________
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