a hypothetical for discussion

[RN]

He's here...

I just did a dive in Ginnie on CC where I reserved 400 cubic feet to travel 4800 feet. I made it out with under 100 cubic feet left. In theory, I used about 3 times the amount of gas that I should have. It's a long story why, involving some restrictions that took longer to get past than I was expecting, an unintended jump and a flooded rebreather... but that's exactly the sort of hellish scenario that reserves are designed for. An even more amazing statistic - of those 300 cu ft used, I used 200 cu ft "navigating" (poorly, with a very screwed up head) from 4800 ft back to 3200 ft.. THe next 100 cu ft got me to the exit - and even that was due to a ridiculous SAC rate under pressure.

Let me emphasise this - if I had dived with only double the gas theoretically needed to exit, I would have run out somewhere around the Henkel, and drowned. If I had dived with triple the reserves, I would have barely made it. I NEEDED a 4x reserve.

My (somewhat misunderstood) philosophy is to a) work out the bare minimum needed to exit, and b) add whopping reserves onto that bare minimum. In this case, I had 4x the reserves theoretically needed (or, in OC terms, I was diving fifths) and it was nearly not enough.

Ah, the naughty word censors... doo-dah happens. Prepare for it.

BD, I think what a lot of people are telling you is that it's not a matter of routes, its a matter of never going anywhere near thirds in a low flow scenario like Peacock. SPG errors are one of many very good reasons NOT to go to thirds.

Thanks for this great example of why 1/3s is not enough!!!

While we're at it, I've always had a problem with "the thumb." People reach thirds and "give the thumb." But the thumb and the finger twirl mean two different things, and I make sure everyone I dive with knows the difference.

The finger twirl means to turn around. No emergency, just turn around and go out about the same as you had come in. If you lolligagged on the way in, you can lolligag on the way out (although not quite as much lolligagging should happen on the way out).

A thumb means "leave now." Although not necessarily a full-fledged emergency, there's no wasting time getting out. It usually means the diver is not 100% comfortable and wants to be at the surface without much delay.

Exactly!!! I teach my students about this difference. My first sidemount passage in JB had me coming back in zero visibility. I came up to the restriction and hit rock. I backed up and changed direction again, and hit rock again. This happened 3 times before I found the hole I was looking for. Keep in mind I had the line in my hand the entire time! When I popped out I signaled my wife with the thumb. Our usual exit consists of learning what the cave looks like from that direction and also looking for side passages for future dives. We still always get out with close to 2000psi. Well, she proceeded to do this. I signaled a thumb again and she signaled back and continued a leisurely pace out. I finally got in her face and signaled one more time. She got it that time. Once back at the surface we decided a twirly finger is the signal for a leisurely exit and a thumb means it's time to GTFO. Unfortunately, there are divers out there that think the thumb is the only appropriate turn signal, instructors included.

Actually that is one of my favoite stories - one that actually does show how independent/sidemount advantage over manifold (the gas loss from both tanks was only posiable due to the manifold).

But IIRC while they were at "maximum penetration" they had turned early on gas. They had more than thirds but ran out before reaching stages (due to bouyancy issues and air sharing). Even after reaching stages they nearly ran out of gas again even though they both had full supplies at that point.

If they had been at thirds when the the accident happened they almost certainly would not have made it. While if they were diving independents/sidemount it would have been a non-event - not even a story worth including.

It's been years since I read the account. Thanks for the clarification. It brings across the point even better!

[Bobby]

Exactly!!! I teach my students about this difference. My first sidemount passage in JB had me coming back in zero visibility. I came up to the restriction and hit rock. I backed up and changed direction again, and hit rock again. This happened 3 times before I found the hole I was looking for. Keep in mind I had the line in my hand the entire time! When I popped out I signaled my wife with the thumb. Our usual exit consists of learning what the cave looks like from that direction and also looking for side passages for future dives. We still always get out with close to 2000psi. Well, she proceeded to do this. I signaled a thumb again and she signaled back and continued a leisurely pace out. I finally got in her face and signaled one more time. She got it that time. Once back at the surface we decided a twirly finger is the signal for a leisurely exit and a thumb means it's time to GTFO. Unfortunately, there are divers out there that think the thumb is the only appropriate turn signal, instructors included.

I use the same signals and learned an important lesson on a dive with regular team members. We had been diving for a few days with the same group of people. On this day another of our regulars joined us fresh out of a class (Apprentice IIRC). We were a little complacent in our dive planning and did not go over the finger swirl and thumb signals. The diver out of the class gave the thumb signal and was questioned to ensure he meant thumb. In his class they had only used the thumb to turn the dives and he had forgotten about the finger twirl. This resulted in added stress for everyone in the team with each of us wondering who was having a problem and what it was. We all made mistakes that day and allowed complacency to enter our diving from familiarity of us diving together.

Bobby

[bletso]

To me it is important to use the two different signals as they are meant to be. One dive a while back I was with a dive buddy and he turn the dive (twirled finger), so I answered and we started out. I made a couple of stops and he became a little antsy and gave the thumbs up signal which changed the tone of the dive. Nothing serious but a he had become very anxious being a newbe cave diver and wanted the hell out of Dodge.

I have thumbed very few dives over the years and reserve the thumb for what it was intended for.

Dale