[PSUBS-MAILIST] Dive report: Snoopy at Seneca

Mon Jun 8 16:41:15 EDT 2015

Brian,I found this pdf on Minn kotta seals which shows two shaft seals.www.minnkotamotors.com/WorkArea/DownloadAsset.aspx?id=3133   
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So if this is the case on Snoopy then yes you would get water past thefirst seal. Or the problem could be air in the cavity between the two sealsthat you wouldn't be able to eliminate.They say the Minn kotta seals are good to 100ft thoughonly rated for about 15ft. But this would depend on age & shaft condition.   The system on Snoopy & some other K boats, is just a flexible tubethat wraps around the motor. So not a great volume as compared to acommercial oil compensation systems.Alan
      From: Brian Cox via Personal_Submersibles <personal_submersibles at psubs.org>
 To: Personal Submersibles General Discussion <personal_submersibles at psubs.org> 
 Sent: Tuesday, June 9, 2015 4:47 AM
 Subject: Re: [PSUBS-MAILIST] Dive report: Snoopy at Seneca

Is there pressure in an enclosed part of the seal? Brian

--- personal_submersibles at psubs.org wrote:

From: Brian Cox 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 09:01:42 -0700

Hmm, guess I'm not getting what is happening 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 10:53:29 -0400

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 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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