[PSUBS-MAILIST] Dive report

Thu May 22 07:00:34 EDT 2014

Thanks for the report Alec & Scott,
I appreciate all the details. 
Alec, could sea water get in to your depth gauge? Do you have oil in the gauge line?
I know what you mean about those lake thermoclines. I dived in to one & literally couldn't see
my hand in front of my face. 
Alan

Sent from my iPad

> On 22/05/2014, at 1:48 pm, Alec Smyth via Personal_Submersibles <personal_submersibles at psubs.org> wrote:
> 
> Hi all,
> 
> I see Scott just emailed a dive report, so here's the Snoopy half of it.
> 
> Summersville Lake was looking fantastic and the weather ideal. I'll attach a low-res photo in the hope it comes in under whatever our file attachment limitation might be. The problem, however, was that this beautiful weather had been preceded by a deluge that raised the water level by fifteen feet in less than a week, ruining the visibility in the process. In consequence, our trip was good for sub testing but not for UW sightseeing and video.
> 
> The first dive of day one was also Snoopy's first dive of the year, and I suspect the particularly harsh winter in an unheated garage took its toll. I had made a number of small improvements since the weather warmed up, but we had two issues on the first day. First, the depth gauge simply didn't work. Its an analog gauge that has been in Snoopy since she was built. I thought there might be a blockage in the line or a problem with the shutoff valve, but eventually discovered it was just the gauge mechanism itself that was "frozen". After taking out the glass and moving the needle by hand the gauge worked, but it will get replaced just in case. The second issue was more serious. When I tried to flood the saddle tanks, the stem of the corresponding ball valve simply sheared off. I didn't even force it, the break happened with very little torque applied. Those who examined the parts later thought it looked like a manufacturing defect. The stem was brass, so corrosion was not a factor. I was still able to dive, thanks to having two independent MBT systems, but that is something I'd consider a significant failure, particularly if it happened in a boat without redundant main ballast systems. As it turned out, we were able to get a new ball valve at the local hardware store, and although the valve body was different to Snoopy's the stems were interchangeable.
> 
> On day two we depth tested Trustworthy. I'll let Scott provide the details of the test, but Snoopy attempted to be the "chase sub" and follow Trustworthy down with Scott as crew. That plan was an utter failure. You would think that even in two foot visibility one could stay with something as big as a sub, or follow the rope down, but in practice it was simply impossible to keep ether in sight -- another lesson learned. In the process we discovered that, while on the surface the visibility was about two feet, forty five feet down it suddenly changed to zero visibility. Diving through the thermocline was like having someone turn the lights off in a room, it was a sudden and clear cut transition. 
> 
> After the depth test I gave a "ride dive" to our support diver, and for fun we just kept going down through the layer of dark water. To our surprise it cleared up again at 125 feet and stayed that way until our max depth of 220. We turned around at that point because the depth sounder indicated we would not find bottom within our 250 foot limit, having another 48 feet to go. The bottom was tantalizingly close to our limit, but we were not going to see it from an altitude of 18 feet. As it was, however, 220 feet was Snoopy's deepest dive to date and therefore of interest performance-wise. The OTS comms continued to be clear, if with a little reverb effect that made the other person sound very distant. The oil compensation in the motors and lights all worked well. The only issue experienced at that depth was a drip from the through-hull that brings the OTS transducer cable into the hull. This through-hull consists of a stainless insert about an inch and a half long that is drilled from the outside with a step drill, to form a conical stepped hole into which I potted the little 1/8" cable. I think there must be an insufficient bond to the cable jacket, since the other end of the cable is potted into the transducer. 
> 
> Speaking of the communications, one thing that bothers me about using a headset inside the sub is that it makes it hard to converse with the crew, yet if the headset is removed it is easy to miss a call from the surface. One of this year's innovations consists of a little amplified speaker that is connected to the headset's line out. This worked well. When the surface called, I could hear them and put on the headset only when needed. 
> 
> Now we had discovered that the layer of dark water had a bottom, we attempted one last dive. With Scott as crew, the idea was to follow one of Summerville's vertical walls down and try to keep the bottom in sight once we broke out of the murk at 125 feet. Our buoyancy was minimally negative, perhaps just a couple of pounds. Things went reasonably well at first, but once into the dark layer the navigation predictably became a challenge. The wall turned to a steep slope, which often arrested our descent. We slowly bounced and dragged our way down the slope. That might sound like a workable if somewhat inelegant method of progress, but Summersville's sloping bottom is not conveniently even, and in fact is strewn with gullies and huge boulders. It gets rather tricky trying to navigate in three dimensions with no visibility at all and no instrument beyond a depth gauge. When SCUBA diving in a blackout environment a diver would use his sense of tact, but in a submersible you find yourself trying to navigate via landings and small crashes instead. If the depth gauge stops and the bow is pointing a little higher than the stern, you've probably hung up by the bow and so you go full astern to get free. That's the most straight forward scenario, but most of the time you just get jolted from some vague direction that is hard to discern since pressure hulls have fewer nerve endings than a diver's fingertips. In poor visibility, you can normally see particles suspended in the water washing past the viewports, and get a sense of movement from them. But in this case we could not even make out particle movement. Other than the vertical movements reflected in the depth gauge readings, we could only detect movement by what I will call the built-in human accelerometers. The problem is, although you can sense movement it is very hard to quantify. For instance, we might both agree it felt like we were rotating to port, yet we would have no idea how many degrees we had turned. 
> 
> When the depth gauge stopped moving and horizontal thrusters wouldn't drag us down the slope, we tried levitating off the bottom with side thrusters and then moving horizontally with the stern thruster, hopefully to land a little further down the slope. That worked a few times, but eventually we found ourselves stuck, without the application of thrusters producing appreciable movement in any direction whatsoever, including upward. That's when you start wondering about getting wedged between boulders or under an overhang, but the reality was less alarming. During Trustworthy's depth test I'd spent an hour running around on the surface with very heavy thruster use in order to keep up with a pontoon boat that was constantly being blown across the lake by the wind, and then motoring back to our intended test site. That and the power consumed during an afternoon of diving had taken its toll, the batteries were fading and therefore the thrusters were pushing far less than normal. We squirted a little air into the saddle tanks and surfaced - time to go home.  
> 
> 
> Best,
> 
> Alec
>    
> 
>  
> <Sub scenery.JPG>
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