Who knows how much flaming i will get on this one, but i will tell it like it is.
I have dove at Devil's quite a few times now, i have hit either a 20-30 feet beyond or before the first set of double arrows for the expressway jump at 1/6ths probably about 10 times, plus multiple dives in the gallery and up to the keyhole. I had two buddies over the course of a recent SB event, one who was full cave, the other intro with doubles as well just like me, but with more dives. They asked if i was ok to dive to 1/3rds or so or plan to be near NDL (bottoms out in the section we dove to around 95ft for a few hundred feet and we were on 32%), one of the reasons i didnt mind was due to the additional gas being available from two potential donors if any of us had troubles, but in the end it was my choice to do the dives with or without reason.
We had previously gone to the first double arrows that day, which might be around 450-500ft or so IIRC. Normally for a dive on 1/6ths i start with 3600 (HP120's), turn at 3000 at 500ft, arrive back out around 2500 if just drifting with the flow or 2700 if kicking along with the flow. The first dive beyond 1/6ths we made it to the beginning of the mudflats (~750ft) and turned before 1/3rds due to not wanting to push NDL or jumping too far ahead in the system. I started again with 3600, turned around 2700 at approx 750ft, and arrived back at 2200 (these estimates are somewhat close as i dont have my log here at work). The reason i got a little further per cuft is due to the flow being down from 500ft onwards due to the hydraulics of the system.
We did the dive again later in the day and got to just before the 4th set of double arrows for the bat's shortcut jump which is around 900ft, i called that one on NDL so i wouldnt go into deco on the way out, again 3600, 2500 and 1900 to end. This incremental penetration is probably about the limit for no deco diving for me, we didnt set goals of reaching x marker or penetration, only the gas, dive time and NDL limits were set before hand and each time we called it early on those counts just due to feeling we had seen/done enough for the dive and just enjoyed the trip out. It sure was some pretty cave. Whilst in there of course the thoughts came across my mind about a failure and other such events, each one i thought through diligently as to what i would do and was confident that i could carry out those skills that had been drilled into me. In fact later that day i was doing blind lost line drills with others to just get in some practice, i would say that is one of the harder drills.
Like i said if you feel the need flame away, we felt that we werent going too extreme with these incremental steps, but others may feel we were reckless or stupid. I wouldnt push this far or fast with Peacock as i dont know the system as well and with less flow its a bit more risk in my thoughts, but i have been asked to dive 1/3rds there as well.
BTW - Andy, are you trying to find loopholes in all the rules? At this time i havent done gaps across caverns, but probably would do. Beyond this pushing of gas reserve limits i stick to the set in stone scuba police rules, i understand the stats, the genesis of the rules and have read quite a bit further about cave diving to understand the risks and considerations to make in many of the decisions involved therein. I will take my full probably sometime later this year or early next when i have the free time and additional cash to not only do the full course but also the adv nitrox/deco and buy deco set-ups etc, probably a good $1000-1500 there.
