Re: [PSUBS-MAILIST] Reserve buoyancy

The one serious pod leak with PC9 (that was the only one I had out of several thousand dives where I was either pilot, deck crew, mechanic or crew chief) was caused by leaking closure 0-rings. In that case, there was actually a paper matchstick across the sealing surface. Time pressure, rough weather and outside distractions were the causes. Somebody wasn't paying enough attention, but there were mitigating circumstances. Aren't there always?

The real problem was not the leak, which should have been detected before we were deployed. It was another one of those faulty mind things. My pilot and instructor on that dive checked the leak detection system during his pre-dive and then switched them off for lunch. He forgot to turn them back on so we were on the bottom of the Auk Field when things began to feel sort of heavy on the port side. We estimated the pod filled about 1/3 of the way up, maybe 1/2. PC-9 had very large MBTs and we were able to blow them dry and power up for recovery. We did get green gas out of the pod, however. That'll make you nervous.

Other issues with that and other submarines were caught at the surface. The sub was partly launched and the predive finished as we sloshed around, especially the leak detectors and so on. We did not have the penetrators to pull a vacuum on each pod, which would solve the problem on deck (or on the trailer). The Deepworkers pull that vacuum in the hull every time they dive. You can do it with a vacuum cleaner and it ain't a bad idea for us backyard guys who don't have a 20-ton A-frame, a 1500 ton ship, or a 9-man submarine crew standing around waiting to fix each other's screw ups.

In short, maintenance is a key issue and attention to detail is essential. Keep the paint pretty, the O-rings greased and your hands clean while working on that stuff. Even grit can cause seepage, even on a fat o-ring. I'm rigging mine to charge with the batteries open or closed, and that means plumbing for air to move through. That same plumbing could be used with an adapter to pull a minor vacuum and test for leaks.

Vance

-----Original Message-----
From: Sean T. Stevenson <cast55@telus.net>
To: personal_submersibles@psubs.org
Sent: Sat, Dec 5, 2009 1:01 pm
Subject: Re: [PSUBS-MAILIST] Reserve buoyancy

Vance, I'm curious about the failures (leaks, etc.) you encountered while working. Could you list some of the significant ones?

-Sean

vbra676539@aol.com wrote:
> You want a positive metacentric height under any forseeable > circumstance. Assuming a drop weight designed to equal a flooded pod, > and mounted in roughly the same area, then your metacentric height > won't change at all except by the tilt of the sub toward whichever > side is flooded. That extra weight will shift the metacentric, as it > will move the center of gravity and the center of buoyancy must then > also move to the new center. If the pods are wideset like on a Perry > or the Aquarius (or the Deepworkers, come to that) then this tilt to > one side will be fairly major. It will not, however, cause the > submarine to turn over (assuming acceptable distance between CG. A > proper design could conceivably be inverted, but it would right itself > automatically. But what a mess in the pods! And let's hope none of us > has to take that particular ride.
> > A side issue to this, but an important one, is a partially flooded > pod, which is in fact a whole lot more likely scenario (a slow leak > that you don't pick up on until you've been in the water a while). In > my experience, you end up with all the water in one end of the leaking > pod as you surface, which sticks your nose or tail up whether you have > dropped a weight or not. That's when a couple of inflatable surface > floats come in really handy. They can get the sub even enough for its > pilot to escape or for the surface crew to tow you or lift you out of > the water or whatever. It is also a neon bright advertisement for leak > detection in each pod!!!
> > Vance

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