[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Mon Jun 8 10:53:29 EDT 2015

Explained in the original post!

On Mon, Jun 8, 2015 at 10:30 AM, Brian Cox via Personal_Submersibles <
personal_submersibles at psubs.org> wrote:

> How could it possibly get pressurized then?
>
> Brian
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
> Date: Mon, 8 Jun 2015 08:00:17 -0400
>
> Hi Brian,
>
> If I understand you correctly, that is exactly what I have.
>
>
> Best,
>
> Alec
>
> On Sun, Jun 7, 2015 at 11:30 PM, Brian Cox via Personal_Submersibles <
> personal_submersibles at psubs.org> wrote:
>
> Alec,
>           Why don't you just have the motor open the ambient water instead
> of trying to seal it?  Couldn't you just have a small reservoir above the
> motor for the compensating oil?
>
> Brian
>
>
> --- personal_submersibles at psubs.org wrote:
>
> From: Alec Smyth via Personal_Submersibles <
> personal_submersibles at psubs.org>
> To: Personal Submersibles General Discussion <
> personal_submersibles at psubs.org>
> Subject: [PSUBS-MAILIST] Dive report: Snoopy at Seneca
> Date: Fri, 5 Jun 2015 18:16:04 -0400
>
> 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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