Kevrumbo(Offline)

Oil Rig Eureka on the Psalty V six-pack diveboat Sunday 09 March. Visibility at depth was 30’/15m with fair water clarity, water temperature 52deg F/11deg C. Used 26/14 NAUI Helitrox and Oxygen deco. NAUI RGBM Table Profile for 120’/36m looks like this:

Depth: Time (min):
120’/36m 30
(--ascend 30fpm/9mpm—)
40’/12m 2
30’/9m 3
20’/6m 3 [O2 switch]
10’/3m 5

Ratio Deco 1:1, which was actually utilized, looked like this:
120’/36m 30
110’/33m 0.3
100’/30m 0.3
90’/27m 1 [75% of max depth deep stop]
80’/24m 1
70’/21m 1
60’/18m 3 [50% of max depth deep stop]
50’/15m 3
40’/12m 7 [35% of max depth deep stop]
30’/9m 7
20’/6m 5 [O2 switch]
10’/3m 3

Ratio Deco/Minimum Deco Algorithm generated similar progression as RD 1:1 above, but with a slightly longer Oxygen period total of 11min with shorter deep stops of 5 to 10sec; 2min; and 5min (75%, 50% and 35% of max depth respectively). Assumed 10% EAD for the 26/14 Helitrox (i.e. 15min NDL).

Scootered around the perimeter of the Oil Rig, as well as a few “jousting runs” through the support columns, horizontal cross-bracings and rows of drilling tubes (structure as usual beautifully adorned with strawberry anemones, scallops etc. –a sea lion to play with and only a few Rockfish with a couple of monster Sheepheads were seen).

Foggy morning but cleared quite nicely. Counter prevailing Santa Ana conditions [similar weather to the Mediterranean Mistral] flattened the swells to 3’ with an occasional 5 footer in the AM, with increasing frequency in the afternoon. Had no problems holding the 20’/6m Oxygen deco stop in the surge of 2' to 3' at depth (those of you So. Calif. divers familiar with Oil Rig Eureka know there's no effective shelter at depth from this surge, which can vary your 20' stop depth 10' to 15’ on “normal” days. . .. )

Here are some nice representative pictures of diving the Oil Rigs in Southern California from Kalani's Scuba Photos. . .

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tim(Offline)

Wow, I'm envious :-) I got to do that exact combination in October '06 after a compressor failure cancelled our planned trip to Farnsworth, and as a 'second best' I was blown away by the site. All I can think of to compare it to would be the most monumental underwater cathedral in the world. We just hung at about 20m and watched huge shoals of sardines in the depths below us being hunted by birds and sea lions who would stop to look at us on the way bac to the surface. Those photos bring it back - though I suspect we were lucky on viz as we were able to clearly recognise divers across more than the full width of the rig, and were having fun exchanging light signals over huge distances. I easily rate it in my top three best temperate water dives!

Absolutely stunning dive, and nice to be reminded of it. Thanks!

Tim

LCF(Offline)

Wow, the NAUI tables have half the deco of Ratio Deco! The NAUI schedule seems pretty aggressive to me, although what do I know . . .

Sorry you had such limited viz. When we did Eureka, we had about 100 feet of viz, and it was like being in a fantastic science fiction movie to hover and look down through row after row of structure contrasting with the deep, clear blue water.

Peter's biggest fear on that dive was sitting on deco and worrying about a sea lion diving in on top of him

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Kevrumbo(Offline)

That's great to hear Tim (and Lynne)! Glad you had a good dive on the Oil rig (even with the diversion from Farnsworth Banks, backside Catalina Island)!

It's a fabulous structure with abundant Marine Life to behold on good visibility days at depth; however IMO, the Eureka Oil Rig can be the most challenging and treacherous "Washing Machine Dive" in all of Southern California --unpredictable, changing eddy upwellings and down currents at depth; the potential 3m surge at safety stop depth; essentially bottomless at nearly 200m deep; together with open ocean swells, currents, and fog on the surface-- all close by to the shipping lanes of two of the busiest Ports in the world (Los Angeles and Long Beach Harbor).

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limeyx(Offline)

1/2 that deco is actually about right.

2 ways to figure this one.

120 for 30 on 21/35 or 18/45 with 50%
= 30 mins (if you were at 150) - 15 mins (30 feet shallower) = 15 mins on the 50% bottle and 1 min at 90, and 1-2 @ 80

or using O2

NDL for 25% @ 120 = 15 mins (taking a 10% EAD) so you need 15 mins BG deco + deep stops, or 8 mins on O2 (5 on @ 20, 3 up)
but in this case I dont see the need for all that deco at 60, or the 7 min stops at 40,30 honestly.


the NAUI table is not that far off, if they had deep stops from 80 or so feet of 1's at 80,70,60 and maybe 2's at 50,30 (remember, the Ratio Deco deep stops are for # of mins *over* NDL, not total dive time, so you have 15 mins over an NDL of 15 mins, so deep stops are really pauses @ 75% of depth, and 1's from 50% up to O2

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rjack(Offline)

Yes, the 1:1 setpoint is totally inappropriate for 26/14.

If I had been forced to use the non-standard 26/14, I would have used -10% EAD for 15min of MDL time at 120. But so with 30mins BT you needed 15 + 7 mins ascent = 21 mins total deco.

But you need to shape roughly like this because the deep stops have been extended to 1mins from 50% of depth. You need not do those 7 min extended stops at 35% depth for this exposure.
60-1
50-1
40-2
30-3
20-6
10-8

The O2 halves the time spent up there so its
60-1
50-1
40-2
30-3
20-7 on O2
5 mins to surface

Total time = 21 mins deco. The whole plan would have been much better on 50% instead of O2.

limeyx(Offline)

right. same plan here, almost to the minute.
But again for that runtime, the O2 doesn't give you too much benefit as not much slow-tissue loading occurs, and 50% gives very similar deco time and may even lower min gas (I didnt really calculate that)

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Kevrumbo(Offline)

Hi Richard and Nick, and heartfelt & sincere thanks for your input and comments!

FYI the 26/14 NAUI Helitrox mix resulted from an air top-off of old 30/30 Triox in Dbl 95's; and my AL40 of 50% was used up in last weeks Sacramento Dive to 200'/60m (and that AL40 tank now needs a Visual Inspection/O2 Cleaning so I couldn't get a Nitrox 50 fill). My only deco gas left was half full an AL40 of Oxygen, so I decided -what the heck- let's give it a go and see how flexible Ratio Deco is with mixes in the "Tecreational" Range.

Also made a decision with to go with RD 1:1 as it turned out to be the more conservative of the calculated profiles above (despite Richard's opinion that its utilization was "inappropriate") . . .and due to the challenging nature of a dive on the Eureka Oil Rig, I profess that such caution is prudent and advisable.

The reason why I chose 7min in RD 1:1 (and 5min in the Minimum Deco sub-Algorithm) for 40'/12m and 30'/9m was AG's instruction to hold to a linear deep stops progression per the WKPP Table, until you intercept an O2 Window Curve (50% Nitrox for example); or gradient curve (i.e. "pushing the ambient pressure gradient", coming shallow to the surface on backgas exponentially a la Buhlmann); or in this case, the Oxygen Switch & Deco Stop at 20'/6m. However in hindsight, 3min or 4min instead of 7min at both 40'/12m and 30'/9m probably would have been okay and still within prescribed profile calculations of the RD 1:1 or Minimum Deco Schedule with O2 for this dive.

BTW, I used the NAUI Table Profile instead for determining a Minimum Gas Reserve (MGR) to 20'/6m (yielded an absolute SPG value of 60bar "Rock Bottom"). . .

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Kevrumbo(Offline)

Some topside "prep/jump-off" pictures of a previous Eureka Oil Rig Charter, with a few DIR divers & the local GUE Instructors (Karim Hamza and Michael Kane, aka "MHK"):

http://www.divematrix.com/showpost.php?p=29051&postcount=11
http://www.divematrix.com/showpost.php?p=29052&postcount=13

And some great wide-angle diver/scooter and macro shots by Ken "Mo2vation":
http://www.divematrix.com/showthread.php?t=2772
http://www.divematrix.com/showthread.php?t=2777

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Diving Dave(Offline)

Second that. It reminded me of the alien artifact from Total Recall. Only full of amazing life (no three breasted woman as far as i noticed though). I was completely in awe.
Particularly apt as it was that trip that convinced me of the way of the dark side. Tim, I hold you partly responsible for the atrocious state of my finances ;-)

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