[PSUBS-MAILIST] Depth tests at Seneca

[Alec Smyth via Personal_Submersibles]

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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