[PSUBS-MAILIST] Depth tests at Seneca

Mon Aug 30 19:16:17 EDT 2021

Another fun thing was that Cliff got to take a dive in Shackleton. Maybe he
can give us a review, a la Road and Track or such!

:)

On Mon, Aug 30, 2021 at 5:38 PM Alan James via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> Great report thanks Alec.
> Glad you survived the battery pod flooding, that could have been
> expensive.
> I know GL had a similar rule to what you are saying ABS has, but it was
> that any compartment (apart from the pressure Hull) that can flood has to
> be able to be mitigated by drop weights etc. Can't remember the exact
> wording.
> Good to hear & learn from the fails.
> Thats a pretty good check list for testing;
> it should be up on the Psubs site somewhere.
> Alan
>
> On Tuesday, August 31, 2021, 09:18:56 AM GMT+12, 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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