[PSUBS-MAILIST] Dive report: Snoopy at Seneca

[Alec Smyth via Personal_Submersibles]

Hello friends,

I just got back from a dive trip to Seneca with Dan Lance and thought I'd
share how it went. This was supposed to be a two sub trip with Scott
Waters, but unfortunately a business emergency intervened and it ended up
being just Snoopy.

On the way up the weather was terrible, with driving rain so heavy I could
barely see the lines on the road. It had been raining heavily for several
days previously. Three times there were emergency announcements about
floods, large hail, and damaging winds, and the closer I got the harder it
rained. The problem with all that rain is that in your typical lake, the
runoff ruins visibility for weeks. That is what happened last year when
Trustworthy and Snoopy rendezvoused at Summersville Lake, and it looked
very much like this would be a repeat. I'm happy to say Seneca must be
rain-proof, because the deluge only reduced the visibility in the top fifty
feet or so, and even those were clearer than most lakes.

Here's a few things we learned:

1) Of props and shrouds
The stern thruster speed control was dead on arrival, although I had tested
it successfully before leaving. I opened up the enclosure, pressed down all
the spade connectors, and found it now worked - so attributed the issue to
road bumps. However, it died within a minute on the first dive. I had a
spare speed controller, so switched it out.

The replacement died within five minutes on the second dive. This time at
least the cause was obvious, the prop was jammed by weeds. The current
Minnkota props have a little twist at the end of the blades, and Snoopy's
shroud is made with almost no clearance. The little twist to the blade tip
causes any object coming between prop and shroud to jam tight, and had
already smoked one controller during the convention in the Keys. I'm going
to put the prop on the lathe and take off the tips to eliminate the
pinching effect and to reduce the amperage draw a little so the motor goes
lighter on the speed controller. By the way, the speed controller was
protected by a fuse rated a little below the controller spec current draw,
so perhaps those specs are optimistic. Anyway, as a result of the double
failure all of our dives were done on just the side thrusters because I was
out of spare speed controllers. Lesson for next sub: Design the electrical
system with a controller bypass, so I can operate thrusters with simple
on/off switches if a speed controller fails. They're electronic, they *will*
fail.

2) Of air bubbles in compensation oil
Snoopy is now routinely diving deep (250 ft) and this has showed up a
puzzling issue with the thrusters. They were feeble during dives, one died
altogether on one dive, and they kept coming up leaking oil. At first we
thought the seals were failing, perhaps due to some chemical
incompatibility. We found suitable seals at an Amish farm supply store that
sold things like tractor spares (viva trolling motor simplicity!) When I
disconnected the bladder hose I got quite well sprayed with oil. The motor
turned out to be pressurized.

Previously, I thought if one had a small quantity of air left in the system
it would not be an issue so long as the compression volume of that air
could be handled by the flexibility of the hose (aka compensation bladder.)
Wrong. I now think what happens is that if the dive exceeds the pressure
rating of the shaft seal and there is a bubble of any size, you will get
water added to the oil *and the bubble stores the pressure*. Upon
surfacing, the bubble squeezes oil and water back out until the pressure in
the motor falls to the "cracking pressure" of the seal. Thus, you get an
oil leak even though the seals are fine. Lesson: Zero tolerance with oil
bubbles, even a small bubble is unacceptable if you are diving deep. I'm
going to put set screws on the motor caps so I can get rid of the bubbles
more easily.

3) An easy way to add buoyancy
Snoopy's buoyancy is adjusted by placing trawl floats in PVC tubes. On one
occasion, the oncoming passenger's weight required the addition of just one
float (i.e. the new guy weighed seven pounds more than the one getting
off). The support diver wasn't suited up and the water was 42 degrees, so I
just pushed a float under the lip of the forward MBT. It worked like a
charm, and the float even stayed in place throughout the tow back to the
ramp. Lesson: You can easily add a few floats for buoyancy on a standard K
sub, no special tubes required.

Most of our dives were along a very steep incline, not quite a wall but
more like a series of ledges and very steep slopes. Between the steep
terrain and the good visibility, the K250 dome for once offered a really
good view. We typically made our way down the slopes using very slightly
negative buoyancy, trailing the back corner of a skid on the slope. Looking
aft, you could see a zigzagging trail of silt hanging motionless in the
water and tracing our path. The sub compresses with depth, so slightly
positive buoyancy at the surface turned into slightly negative at depth,
but we're speaking of just a couple of pounds and not anything that caused
difficulty. In fact at one point we stopped dead in the water four or five
feet above a flat bottom for about five minutes, just waiting for a
pre-arranged touch-point call on comms. The sub didn't rise or sink an
inch, she just hung there completely immobile for five minutes. At about
140 feet the visibility would improve significantly, and the water changed
from green to blue. It looked like ocean instead of lake water. I'll post a
video, but that'll take a few days to put together. The only "incidents" we
had were a cold bath we took when we closed the hatch over a corner of the
crew's shirt, and when we got hooked on a log at 220 feet - fortunately
reversing got us right off it.


Best,

Alec
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