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Deep Dive Planning April 28, 2009

Posted by Chris Sullivan in Dive Log.
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The best of plans can go awry, some by a little, some by a lot. Other than the extra 2 minutes at depth, a result of not being able to find the way into the escalator and compensated by shortening the next segment of the dive, I thought we were pretty close to our plan. Well pretty close is right, but not by any means on it.

I’ve charted both the plan and the log of the Oriskany Dive #2, which I described in this blog a few days ago. The blue line is the actual dive (painstakingly recorded from the dive profile on my Apeks Quantum, which spits out a new number every second representing 30 second intervals of the dive), while the black line is the plan.

The first part I expected, we had a slower descent than planned. I warned the others that this would be the case when we planned the dive, as it always takes a little time to go through the bubble checks and we never rocket down to depth (well, hardly ever), but you can see we’re almost 8 minutes into the dive before we start the descent down the escalator from 150 to a maximum depth of 172. We had planned to assemble at 100 and then 3 minutes into the dive go down the escalator, so at this point we were 5 minutes behind schedule. Given that there were 5 of us, and none of us had done this tour before, it was inevitable that we’d be late.

Then you can see that we were about 2.5 minutes behind getting back to the deck of the ship, and above our next planned depth of 150′. After that we were pretty good. We were again late on our ascent to our deco stops by about 2 minutes. Now the dive plan as shown ignore ascent time, which would have added 5 minutes to the dive, so I can account for some of that there, but at 40 feet we’re considerably behind and I’m not sure why. One theory I have is that my watch lost time – I missed my train from work on the first day back and found my normally precise watch (1 second a month) had lost 3 minutes. I think there may be a problem with it under high pressure, even though it’s rated to 200 metres.

The stops also really look unsteady. They were crowded and I was constantly repositioning myself but I think I can still do better. Obviously more practice is required. Fortunately both the gas plan and the computer were conservative so I had a very extended deco courtesy of the computer, and still arrived with almost half my back gas remaining.

I don’t have the dive plan for dive #1 although I’m trying to get it from one of the other divers. I’d like to see how that one went.

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1. Deep Dive Planning #2 « Chronicle of an older diver - April 29, 2009

[…] Technical Diving, Wreck Diving trackback This is actually in reverse order as I described the plan for dive #2 yesterday, but I’ve obtained the dive plan for Oriskany Dive #1, and combined it with the plot from my […]

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2. Gradient Factors « Chronicle of an older diver - May 4, 2009

[…] to use my computer to compare my dive against the plan like I did with Oriskany dives #1 and #2. This is good discipline, I […]

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