[PSUBS-MAILIST] some further lake tests

Thu May 19 07:21:57 EDT 2016

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 we drove to the same lake as the first to do some more test
> dives for our little human 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 to the harbour’s launch slope on a bumpy path, we heard a
> noise a km before arriving. We found out that our 100kg emergency drop
> weight had fallen from the sub. Hopefully it only fell 15cm onto the
> central beam of the trailer, from where it could not go anywhere… The
> vibrations had moved the release pins, and it also moved apart by a few mm
> the lower legs of our nose frame, which normally closely bound each side of
> the drop weight and where the release pins go. With a few hands we pushed
> the weight back up in place. Lesson learned: use longer pins, retighten the
> frame and add a thread bar to keep the legs of lower frame close enough
> together. Also, we should have the drop weight rest on 3 support points (2
> pins, 1 ledge), not 4 (2pins, 2 ledges) which will never be fully stable.
>
> -We then launched. It went smoothly as we had done it before and knew
> exactly where to bring the trailer and its rope extension to have the sub
> float.
> We then deflated the 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 and recomputed the lead weight we needed this time
> given all the food and stuff we had taken.
>
> -then the boat towed 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 prop shaft, which was there regardless of
> rotating speed, but only when pedaling in the forward direction. It was not
> there during the first dives, and it disappeared the next day. We are
> wondering whether it came from the water lubricated bearing , or the
> pressure seal assembly. The length of the prop shaft of over 2m makes it
> probably prone to resonance.
>
> -This time we had better navigation instruments, a compass mounted right
> outside the dome in front of us, on the aluminium dome seat, with quite
> lower magnetic deviation due to the hull than we feared. Also a diver depth
> gauge was there, very useful. We were eager to test our imagenex
> sonar/sounder combo, but could not get it to work for that dive. Will be
> next time…
>
> -The sub turned out quite stable, keeping straight when we stop pedaling,
> but we noticed that having a buoy attached at the front of the sub with a
> short rope to remain clear of the propeller gave a bit of instability on
> top of extra drag. Depth control worked 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 to rework a bit the handle so it is
> more convenient to use, especially when the sub is at large angles.
>
> -The oxygen consumption turned out lower than we expected. Michael and
> myself are quite lightweights I should say. We were running at 0.75L/mn for
> 2 people at rest, it actually went down to 0.5L/mn during the night, with
> one sleeping. It also shooted up to 2L/mn after I went out for a swim
> around the sub in cold water to remove our buoy rope from the prop the next
> day. So feeling warm is really good to lower oxy consumption, and a down
> jacket, socks, hat and gloves may be worth kgs of sodalime in emergency
> mode! When pedaling it ranged between 1.25 to 2L/mn, not as high as
> anticipated, but the pedaling resistance and heart rate remained quite
> moderate. This brings our ‘theoretical’ life support autonomy to a whopping
> 16 days in pedaling mode, and 37 days in rest mode.
>
> then we went for a tow to a nice diving spot on the other shore of the
> lake where we would spend the night and find deeper water for the next days
> dives. The tow was quite choppy, and we occasionally dove a 0.5 to 1 m with
> dynamic effects, although since the first dives we moved the towing point
> below the nose tip which improved considerably the behavior under tow. At
> some point we had to slow down the tow as we noticed that the dome had
> slightly moved on its seat, under a combination of : effect of slight
> internal overpressure caused by temperature increase due to sun light in
> the dome and slight CO2 build up, wave action, occasional UW dips, and
> primarily because the force on the dome retainer strap was not high enough.
> When we arrived at the other shore, we moored, inflated ballasts and
> delicately removed the dome to check the oring and force on retainer strap.
> We noticed the oring had a pinch point towards the dome pressure seat, so
> we cleaned and re-placed it in a way to keep low pressure tightness. We
> also added 1mm spacer between the dome and retainer strap to increase the
> strap down force, and ensure a large enough oring compression so the dome
> rests on its seat with no gap. the general theory says that a gap should
> not be an issue as when you dive, the force closing the gap should be many
> times higher than 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 removed the prop to see if some debris could have caused the
> subtle vibrations, but could not find any thing.
>
> -After that we had dinner and landed the sub to spend the night near the
> shore in less than 2m water depth. Deployed our anchor also to stay put. It
> worked well. Inside the sub we deployed our bunker bed and tested switching
> positions between Michael and 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, after a beautiful sun rise seen from underwater, we went for a
> dive to 10m water depth where we could have space above and below us to
> really operate the water ballast and trim weight tray on rollers. Thanks to
> our depth gauge, water circuitry and hand pump we could get in trim within
> less than 1 kilo, and feel the inertia of piloting moves. It was really
> good feeling piloting that thing in three dimensions. After the dive we
> surfaced with our ballast and pedaled we got the rope in our large prop,
> which led me go out, take a swim to cut it, and shorten the buoy rope as
> our dive support boat had not arrived and our dive support was on the
> shore. We ll probably add a duct around our prop... Then before I came back
> in, some fishermen in another boat came and asked us whether we were fine,
> they initially thought we were a boat upside down. It was funny seeing
> their hallucinating faces.
>
>   -we then had our own support boat come over and we went on for a
> stretch of pedaling at 2m water depth. We could measure our speed at 1.2kt
> which falls in the ball park we anticipated. We may gain some without a
> buoy, and once our composite shells are polished, and also with a more
> stable steering than what we had (the short buoy rope attached to the front
> of the sub made it difficult to keep a stable course). On the other hand
> adding a duct around our large prop may decrease our speed. But a duct
> would also increase a bit the power we can put in 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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