Kevrumbo
Banned
- Messages
- 5,659
- Reaction score
- 1,361
- # of dives
- 1000 - 2499
Note: Review sticky first before replying. Cynical non-objective, irrational, post-hoc, and ad hominem attacks will not be tolerated. . .
Under partly sunny skies with gathering clouds, we dropped on a permanent surface buoy/mooring line, and finned over a distance of 15yds to the wreck's bow area. After resting a few minutes at the bow gun, we proceeded to the Tanks and then below to inspect the forward holds crammed full with ordnance & ammunition (depth range 45m/150 to a max of 51m/170')
Upon nearing the 30min Bottom Time mark, I looked at my buddy just as he exhausts his AL80 Stage and switches to his long-hose & Backgas Supply. Hmmm . . .wow I say to myself: He's relaxed & has a great breathing DCR (Depth Consumption Rate) going on. We kept a constant depth of around 45m/150 for the elapsed 30 minutes so far, and were just basically floating neutrally buoyant with very little finning while exploring the forward deck area . . .so I made the decision to extend the Bottom Time from 30min to 50min, or hitting MGR/Rock Bottom whichever came earlier.
I wrote in my wetnotes and communicated to my Buddy, "Re-calculate Ratio Deco 1:1 for 160 . . ." My Buddy signaled & acknowledged okay.
[Lessons Learned: 1) An Error of Omission: I should'vd wrote, "Re-calculate Ratio Deco 1:1 for 160 with Bottom Time 50 minutes. 2) An Error of Commission: Don't place a burden of re-calculating an entire Deco Profile on both yourself and your Buddy especially when you're both narced out-of-your-mind on Deep Air at max depth. At most, just figure out the Deep Stops to perform by looking at your WKPP Table in your wetnotes, then get to your Eanx 50 deco gas switch at 21m/70' and then as the narcosis eases, finally start re-calculating the required profile times needed on your Nitrox 50 and subsequent Oxygen Deco Stops. Better still, use a tech computer with a similar algorithm to your calculated decompression profile for back-up]
I exhausted my AL80 Stage bottle at around the 35min mark, and gave the Leader of the other group the sign, "Watch Me --Switching to Backgas", test purged my primary reg, breathed it and exchanged okay signs. I looked around for my Buddy and saw him finning towards the bow and caught up with him, both of us exchanging okay signals. Looking back, we lost sight of the others, so we finned back toward the bridge area almost to the aft facing end of the superstructure; they were long gone, probably exploring the engine room or aft cargo holds. I then signaled to my Buddy that we return to the bow at depth 45m/150'. Hopefully we would rendezvous with the other group before starting ascent.
50 minutes elapsed time was approaching and I was nearing MGR (Minimum Gas Reserve); my Buddy was past MGR and approaching Rock Bottom Limit (2000psi and 1500psi respectively on backgas), and still no sign of the other Group . . .I called ascent to Deco 36m/120 and made the pinky sign to my Buddy who emphatically signaled okay. We ascended up the forward mast.
Average Depth and Deep Stop Profile looked like this:
48m/160 50min
(ascent to 36m/120 @ 9m/min; 30'/min): 1.3min
36m/120 2min [75% Deep Stop]
33m/110 2min
30m/100 2min
27m/90 3min
24m/80 5min [50% Deep Stop]
(Note: at about the 33m/110 level of our Deep Stops, we noticed the other group signaling above us, as they had already started their deep stop deco sequence while swimming back from the aft cargo holds forward to the bow.)
And now, the Eanx 50 switch and the Fateful Blunder: I signaled seven minutes deco time. My buddy queried back, "Seven?" I signaled again definitely seven minutes. Buddy looks at me with a puzzled face; and this is where it all started to go wrong for me-- with the fist-to-forehead signal, I yielded and gave back control of the Deco Stops to my Buddy. He gets out his wetnotes and starts doing some scratch arithmetic, and then writes out a 4, 3, 3, 3, 4 minutes time sequence for the 21m/70 stop thru to the 9m/30 stop. [Lesson Learned: again I had the greater experience utilizing Ratio Deco on this particular dive and should have insisted on taking over lead and captaining the deco; I'm not quite sure why I conceded to this revised profile when it felt all wrong to me intuitively ("Deer in-the-Headlights Syndrome": you're overwhelmed cognitively and fail to act decisively, despite realizing an immediate threat to your safety.]
Nitrox 50 Segment revised profile was performed like this:
21m/70 4min (switch to Eanx 50)
18m/60 3min
15m/50 3min
12m/40 3min
9m/30 4min (or 2:2 with Backgas Break)
What I wanted to do was this:
21m/70 7min (switch to Eanx 50)
18m/60 6min
15m/50 6min
12m/40 6min
9m/30 7min (4:3 Backgas Break)
Or better yet, a S-Curve Sequence:
21m/70 9min (Eanx 50 switch)
18m/60 9min
15m/50 3min
12m/40 3min
9m/30 6min (3:3 Backgas Break)
So all in all for the Nitrox 50 Segment, only 17 to maybe 20 minutes total time was spent; it should have been at best an optimal 30 minutes!
This was my fourth career non-overhead Deep Air Dive on the San Francisco Maru, called the "million-dollar wreck" because of the amount of war material contained in her holds (Mines, Torpedoes, Aerial Bombs), and for three Tanks on her deck which are probably the most photographed deep wreck WWII fighting vehicle artifacts in the world. My Buddy and the rest of the group of three (two Open Circuit Divers and one on CCR) were going to be experiencing the effects of Deep Air diving beyond 39m/130 for the first time, so I initially planned to stay only on the forward deck areas where the Tanks were, eschewing the Grand Tour circumnavigating the deck from stem to stern. The bottom profile was conservatively planned for 54m/180 to account for my Buddy's higher SCR rate (21L/min or .75cf/min) using Ratio Deco 1:2 Schedule. I delegated the captaining of the Deco Profile to my Buddy. [Lesson Learned: since I had the most experience on this particular Deep Air dive, I should have been in control of the Deco Profile and not given the responsibility to my Buddy.]Overview, 12 Oct 2008:
DCS type I bends hit, left Shoulder/Upper Arm and Elbow suffered after non-optimal decompression profile time spent at depth. Ratio Deco 1:1 Schedule was recalculated at depth to account for an elective extension of Bottom Time, from originally 30 minutes to 50 minutes at an average depth of 48m/160'. Upon surfacing, the decompression profile was later determined to be 20 minutes too short (approximately 10min short at the Nitrox 50 segment from 21m/70 to 9m/30' and 10min short at the Oxygen Stop from 6m/20 to the surface). Deep Stop profile times on backgas turned out to be adequate and performed correctly. Backgas was Air in Double AL80's; Stage AL80 with Air; Deco gases were Nitrox 50 in a full AL80 and Oxygen in a half-full AL63. Original Depth & Bottom Time was planned for 54m/180 and 30 minutes respectively
Under partly sunny skies with gathering clouds, we dropped on a permanent surface buoy/mooring line, and finned over a distance of 15yds to the wreck's bow area. After resting a few minutes at the bow gun, we proceeded to the Tanks and then below to inspect the forward holds crammed full with ordnance & ammunition (depth range 45m/150 to a max of 51m/170')
Upon nearing the 30min Bottom Time mark, I looked at my buddy just as he exhausts his AL80 Stage and switches to his long-hose & Backgas Supply. Hmmm . . .wow I say to myself: He's relaxed & has a great breathing DCR (Depth Consumption Rate) going on. We kept a constant depth of around 45m/150 for the elapsed 30 minutes so far, and were just basically floating neutrally buoyant with very little finning while exploring the forward deck area . . .so I made the decision to extend the Bottom Time from 30min to 50min, or hitting MGR/Rock Bottom whichever came earlier.
I wrote in my wetnotes and communicated to my Buddy, "Re-calculate Ratio Deco 1:1 for 160 . . ." My Buddy signaled & acknowledged okay.
[Lessons Learned: 1) An Error of Omission: I should'vd wrote, "Re-calculate Ratio Deco 1:1 for 160 with Bottom Time 50 minutes. 2) An Error of Commission: Don't place a burden of re-calculating an entire Deco Profile on both yourself and your Buddy especially when you're both narced out-of-your-mind on Deep Air at max depth. At most, just figure out the Deep Stops to perform by looking at your WKPP Table in your wetnotes, then get to your Eanx 50 deco gas switch at 21m/70' and then as the narcosis eases, finally start re-calculating the required profile times needed on your Nitrox 50 and subsequent Oxygen Deco Stops. Better still, use a tech computer with a similar algorithm to your calculated decompression profile for back-up]
I exhausted my AL80 Stage bottle at around the 35min mark, and gave the Leader of the other group the sign, "Watch Me --Switching to Backgas", test purged my primary reg, breathed it and exchanged okay signs. I looked around for my Buddy and saw him finning towards the bow and caught up with him, both of us exchanging okay signals. Looking back, we lost sight of the others, so we finned back toward the bridge area almost to the aft facing end of the superstructure; they were long gone, probably exploring the engine room or aft cargo holds. I then signaled to my Buddy that we return to the bow at depth 45m/150'. Hopefully we would rendezvous with the other group before starting ascent.
50 minutes elapsed time was approaching and I was nearing MGR (Minimum Gas Reserve); my Buddy was past MGR and approaching Rock Bottom Limit (2000psi and 1500psi respectively on backgas), and still no sign of the other Group . . .I called ascent to Deco 36m/120 and made the pinky sign to my Buddy who emphatically signaled okay. We ascended up the forward mast.
Average Depth and Deep Stop Profile looked like this:
48m/160 50min
(ascent to 36m/120 @ 9m/min; 30'/min): 1.3min
36m/120 2min [75% Deep Stop]
33m/110 2min
30m/100 2min
27m/90 3min
24m/80 5min [50% Deep Stop]
(Note: at about the 33m/110 level of our Deep Stops, we noticed the other group signaling above us, as they had already started their deep stop deco sequence while swimming back from the aft cargo holds forward to the bow.)
And now, the Eanx 50 switch and the Fateful Blunder: I signaled seven minutes deco time. My buddy queried back, "Seven?" I signaled again definitely seven minutes. Buddy looks at me with a puzzled face; and this is where it all started to go wrong for me-- with the fist-to-forehead signal, I yielded and gave back control of the Deco Stops to my Buddy. He gets out his wetnotes and starts doing some scratch arithmetic, and then writes out a 4, 3, 3, 3, 4 minutes time sequence for the 21m/70 stop thru to the 9m/30 stop. [Lesson Learned: again I had the greater experience utilizing Ratio Deco on this particular dive and should have insisted on taking over lead and captaining the deco; I'm not quite sure why I conceded to this revised profile when it felt all wrong to me intuitively ("Deer in-the-Headlights Syndrome": you're overwhelmed cognitively and fail to act decisively, despite realizing an immediate threat to your safety.]
Nitrox 50 Segment revised profile was performed like this:
21m/70 4min (switch to Eanx 50)
18m/60 3min
15m/50 3min
12m/40 3min
9m/30 4min (or 2:2 with Backgas Break)
What I wanted to do was this:
21m/70 7min (switch to Eanx 50)
18m/60 6min
15m/50 6min
12m/40 6min
9m/30 7min (4:3 Backgas Break)
Or better yet, a S-Curve Sequence:
21m/70 9min (Eanx 50 switch)
18m/60 9min
15m/50 3min
12m/40 3min
9m/30 6min (3:3 Backgas Break)
So all in all for the Nitrox 50 Segment, only 17 to maybe 20 minutes total time was spent; it should have been at best an optimal 30 minutes!
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