[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Fri Jun 5 18:37:11 EDT 2015

Alec,
Sweet!  
Hank--------------------------------------------
On Fri, 6/5/15, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:

 Subject: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
 To: "Personal Submersibles General Discussion" <personal_submersibles at psubs.org>
 Received: Friday, June 5, 2015, 6:16 PM

 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 shroudsThe 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
 buoyancySnoopy'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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