[PSUBS-MAILIST] some further lake tests

Thu May 19 19:18:16 EDT 2016

Yes,I presume Antoine would have done calculations on this,he seems to have done a good job covering all the bases.Alan

      From: Private via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Friday, May 20, 2016 9:20 AM
 Subject: Re: [PSUBS-MAILIST] some further lake tests

Hi Alan,
Why would it be harder to pedal with depth? Pressure on the shaft seal?
Thanks,
Alec
On May 19, 2016, at 4:56 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Just a few more details Antoine.You were sleeping under the water, are you intending to stay under for the wholejourney or will you be surfacing along the way?What depth will you go down to & what depth will you be travelling at most of the time.It will be harder to pedal the deeper you go obviously. Do you have a film crew making a documentary of the event, other than your own videoing?August is not far away.Alan

      From: Antoine Delafargue via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, May 19, 2016 11:21 PM
 Subject: Re: [PSUBS-MAILIST] some further lake tests

Yes Alan,we will do that between 5 and 12 of August
regards,Antoine
On Thu, May 19, 2016 at 1:12 PM, Alan James via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

Excellent report, enjoyed reading it.Do you have an anticipated date to cross the channel?Alan

      From: Antoine Delafargue via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Thursday, May 19, 2016 9:57 PM
 Subject: [PSUBS-MAILIST] some further lake tests

Hello psubbers,
Last week end wedrove to the same lake as the first to do some more test dives for our littlehuman powered sub. Quite another event rich sequence worth sharing:
-The preparation session went ok. We just had another tv crew, which is fine but is slowed us down, as they often want you to repeat some moves even when they say they just want to film you do your things. Interviews themselves are really short.
-When driving tothe harbour’s launch slope on a bumpy path, we heard a noise a km beforearriving. We found out that our 100kg emergency drop weight had fallen from thesub. Hopefully it only fell 15cm onto the central beam of the trailer, fromwhere it could not go anywhere… The vibrations had moved the release pins, andit also moved apart by a few mm the lower legs of our nose frame, whichnormally closely bound each side of the drop weight and where the release pinsgo. With a few hands we pushed the weight back up in place. Lesson learned: uselonger pins, retighten the frame and add a thread bar to keep the legs of lowerframe close enough together. Also, we should have the drop weight rest on 3 supportpoints (2 pins, 1 ledge), not 4 (2pins, 2 ledges) which will never be fullystable. -We thenlaunched. It went smoothly as we had done it before and knew exactly where tobring the trailer and its rope extension to have the sub float. We then deflatedthe ballasts to check the trim inside the harbour. This time it was perfect,having captured last time’s 25kg discrepancy in our reference excel file andrecomputed the lead weight we needed this time given all the food and stuff wehad taken. -then the boattowed us out, until we reached a 4m water depth to pedal a bit. This went ok.We were just intrigued by a tiny high frequency vibration coming from the propshaft, which was there regardless of rotating speed, but only when pedaling in the forwarddirection. It was not there during the first dives, and it disappeared the nextday. We are wondering whether it came from the water lubricated bearing , or thepressure seal assembly. The length of the prop shaft of over 2m makes itprobably prone to resonance. -This time wehad better navigation instruments, a compass mounted right outside the dome infront of us, on the aluminium dome seat, with quite lower magnetic deviationdue to the hull than we feared. Also a diver depth gauge was there, veryuseful. We were eager to test our imagenex sonar/sounder combo, but could notget it to work for that dive. Will be next time… -The sub turnedout quite stable, keeping straight when we stop pedaling, but we noticed that havinga buoy attached at the front of the sub with a short rope to remain clear ofthe propeller gave a bit of instability on top of extra drag. Depth controlworked well with our 80kg tray on rollers beneath batteries and pilot seat,although we were not aiming for very large swings of depth. We just need torework a bit the handle so it is more convenient to use, especially when thesub is at large angles.  -The oxygenconsumption turned out lower than we expected. Michael and myself are quitelightweights I should say. We were running at 0.75L/mn for 2 people at rest, itactually went down to 0.5L/mn during the night, with one sleeping. It alsoshooted up to 2L/mn after I went out for a swim around the sub in cold water toremove our buoy rope from the prop the next day. So feeling warm is really goodto lower oxy consumption, and a down jacket, socks, hat and gloves may be worthkgs of sodalime in emergency mode! When pedaling it ranged between 1.25 to2L/mn, not as high as anticipated, but the pedaling resistance and heart rate remainedquite moderate. This brings our ‘theoretical’ life support autonomy to awhopping 16 days in pedaling mode, and 37 days in rest mode. then we went for a tow to anice diving spot on the other shore of the lake where we would spend the nightand find deeper water for the next days dives. The tow was quite choppy, and weoccasionally dove a 0.5 to 1 m with dynamic effects, although since the firstdives we moved the towing point below the nose tip which improved considerablythe behavior under tow. At some point we had to slow down the tow as we noticedthat the dome had slightly moved on its seat, under a combination of : effectof slight internal overpressure caused by temperature increase due to sun lightin the dome and slight CO2 build up, wave action, occasional UW dips, and primarilybecause the force on the dome retainer strap was not high enough. When we arrivedat the other shore, we moored, inflated ballasts and delicately removed thedome to check the oring and force on retainer strap. We noticed the oring had apinch point towards the dome pressure seat, so we cleaned and re-placed it in away to keep low pressure tightness. We also added 1mm spacer between the domeand retainer strap to increase the strap down force, and ensure a large enoughoring compression so the dome rests on its seat with no gap. the general theory says that a gapshould not be an issue as when you dive, the force closing the gap should be many times higherthan the force pushing the oring in. But here a combination of waves,overpressure etc may have moved a bit the oring in at some point.We also removedthe prop to see if some debris could have caused the subtle vibrations, butcould not find any thing.  -After that wehad dinner and landed the sub to spend the night near the shore in less than 2mwater depth. Deployed our anchor also to stay put. It worked well. Inside thesub we deployed our bunker bed and tested switching positions between Michaeland I. We slept one after the other, so we could check on O2 and CO2 levels. Comfort was not bad, because the bunker bed is really nice, but space is really small inside. We can grab all the controls and isolation valves in case of emergency, but you can t help but feel like trapped inside... During the night we used the red lighting as in real subs, to feel like in the submarine movies, it was really cool! -Next day, aftera beautiful sun rise seen from underwater, we went for a dive to 10m waterdepth where we could have space above and below us to really operate the waterballast and trim weight tray on rollers. Thanks to our depth gauge, watercircuitry and hand pump we could get in trim within less than 1 kilo, and feel the inertia of piloting moves. It wasreally good feeling piloting that thing in three dimensions. After the dive we surfacedwith our ballast and pedaled we got the rope in our large prop, which led me goout, take a swim to cut it, and shorten the buoy rope as our dive support boathad not arrived and our dive support was on the shore. We ll probably add a duct around our prop... Then before Icame back in, some fishermen in another boat came and asked us whether we werefine, they initially thought we were a boat upside down. It was funny seeingtheir hallucinating faces.    -wethen had our own support boat come over and we went on for a stretch of pedalingat 2m water depth. We could measure our speed at 1.2kt which falls in the ballpark we anticipated. We may gain some without a buoy, and once our compositeshells are polished, and also with a more stable steering than what we had (theshort buoy rope attached to the front of the sub made it difficult to keep astable course). On the other hand adding a duct around our large prop maydecrease our speed. But a duct would also increase a bit the power we can putin at 70rpm, so we might compensate extra drag effect on speed by extra thrust. 
-Over the week end in the sub, we managed to log quite a few hours with our scrubbers. We reckoned we got over 200LCO2 /kg of sodasorb, which is better than the typical figure given by the manufacturer (185LCO2/Kg). The scrubber starts being less efficient indeed at around that amount but we can still manage <1% in the cabin some time after that. On top of that, we have probably extra absorption capacity from our nearly worn scrubbers as we saw it can still run with an exhaust lean in CO2 in parallel or series to our second fresher scrubber. But it is difficult to measure how much we can extend the absorption capacity with this technique. 
regards,Antoine
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