DPV Gas Planning Golden Rule

[victorzamora]

This post in another thread made me curious. I'm very new to the DPV world with no experience, but even I see issues. I've talked to a bunch of people about their strategies and have yet to hear consistent answers from anybody.

Based on some of the discussion I've seen thus far, just wondering if there is not as clear cut rule for DPV planning that, perhaps, is contributing divers to push the envelop unknowingly.

So, I think this is certainly the root cause of (or at least the easiest fix for) many incidents. However, I don't think one clear-cut rule is as easy as I'd like it to be. First of all, cave divers are dumb. I've met a few cave divers that push beyond thirds in high-flow caves because it's easy to exit. That's a simple rule yet violated anyway. We tend to have egos and ignore simple rules.

The other big thing is the added complexity. Even in (swimming) stage diving there are quite a few different approaches. They mostly all boil down to "thirds"...either diving each bottle to thirds or diving stages to half+200 but compensating by keeping fuller backgas to penetrate no more than 1/3 of total gas. But gas planning with buddy bottles gets goofy. Can you push to half+200 and thirds of backgas safely with a couple buddy bottles? If so, how many and where? Does it change in teams of 2 vs 3 vs solo? Then strategies for exit matter as well, right? NOBODY can agree on what bottle to breathe and for how long on exit! Scooters have all of that complexity but with the addition of scooter complications. So, in addition to stages and backgas and buddy bottles....you have to consider multiple scooters and solo vs team and buddy towing as well as quality/speed/range/reliability of the scooters. So a double-stage DPV dive with 3 guys and 2 buddy bottles dropped strategically, the guys are familiar with eachother and practice towing frequently....all diving fancy new top-end scooters that have proven themselves reliable, where do you drop stuff here? How about flow....do you consider flow in your calculations?

So, what woudl it take for you to follow a "golden rule" of DPV gas planning?

[Kelly Jessop]

First of all, cave divers are dumb. I've met a few cave divers that push beyond thirds in high-flow caves because it's easy to exit.

You answered your question before starting. If you know a few, more than one, and they can't follow a cardinal rule, which has very poor conservatism, then you will seen planning rules for DPV that will vary from vague to highly complex untested mathematical models. I thinking the golden rule you seek will be as elusive as the lost city of Alantis, and pink unicorns.

[Superlyte27]

First of all, what are these "buddy bottles" you speak of?

Secondly, my golden rule of DPV diving is very simple.... Always have enough gas to swim out.

[victorzamora]

Kelly: I certainly don't think everybody would follow the rules all of the time, but "rule of thirds" is so much easier to follow than "keep twice the necessary exit gas with you at all times" that something like it, as midway suggested, would certainly help.

Pete: I'm calling "buddy bottles" untouched safety bottles. Not stages, but (often staged) safety gas. And your DPV rule: Do you include flow in that? Do you expect a buddy to tow you out? Do you plan for loop failure AND scooter failure at max penetration? Is your "bailout" team or individual? Do you stage tanks? Also, what SAC and swim rates do you use for your calculations?

[OFG-1]

Andrew Ainslie did a good article on this a few years ago. You can find it here:

http://www.asainslie.com/documents/

Its the article on rethinking bailout.

[nakatomi]

The golden rule is very simple. You always need enough gas to get out of the cave.

As to all the other questions, not only are these answered in a class, there are also drills associated with some of them that are part of the DPV cave class.
Like calculating swim rate, SAC rate under different circumstances. Timing swims while towing out the scooter etc.

[PfcAJ]

Trying to apply overly simplistic rules of thumb (often expressed as a fraction) to complex dives isn't a good strategy.

There's too many variables when it comes to dpv diving.

[Superlyte27]

Victor:

It depends on the cave as to what I "include in that". Each dive has to be planned. So, I can easily swim out of Ginnie or Manatee at 80fpm because of the flow, but can I swim out of Eagle's Nest at 80fpm? It also depends on where I am. Wide open cave swims faster than tight, twisty cave like at Madison. Am I solo, two buddies or three buddies? Because I can't swim as fast trying to keep track of multiple buddies. So, I adjust my swim speed based on several factors like, if & who I have for buddies, the flow of the cave, how tight and twisty the cave is, how silty the cave is. I NEVER EXPECT A BUDDY TO TOW ME OUT. I'd like them too, but every single time I've had a significant issue, my buddy is NOWHERE to be found. Yes, I plan for loop failure and scooter failure at max penetration. Murphy was good at his job. My bailout plan is individual. Read above where every time I've had a significant issue, my buddy is nowhere around.

Do I stage tanks? Depends on the dive. If the dive calls for 200cu' of bailout and I can wear LP85's... No, I'll wear it on me. If the dive calls for 400cu' of bailout, obviously I don't want to carry all of that on me, so I'm dropping tanks the whole way.

So, here's an example of a dive plan at Ginnie:
For easy math, we'll say 4000' at 4ata with a swim speed of 80fpm. My normal swimming sac is .4, so for SHITE HAS HIT THE FAN MODE we'll call it .8
So 4000'/80fpm = 50 minutes. .8 SAC @ 4 ATA = 3.2cu/min 3.2cu'/min x 50 minutes is 160cu' of gas. So, that's assuming two failures. The rebreather has failed at max penetration and my scooter died, and my buddy is nowhere to be found. How many failures do you want to plan for? You can multiply that 160 x 1.5 if you want to assume another failure, perhaps your buddy had an issue. But in the event that your buddy had an issue near you, his scooter can tow you out quicker than 80fpm.

Almost all of my diving is with another rebreather diver. If I'm diving with an OC buddy, I'll always multiply my gas x 1.5. If I'm diving with another rebreather diver, we know that each of us has enough to get ourselves out, it would be really friggin rare for me to need to go to him for gas, or vise versa.

[LiteHedded]

people so badly want there to be an easy to use number to do their dive planning for them. there isn't. thirds is nice in dive classes but just doesn't scale to big dives. neither does carrying gas to swim out.
sometimes you have to actually think about a specific dive and take into account all of the factors to come up with a strategy. there are a lot of caves where you just aren't going to be able to be towed out, or swim out etc.

[Superlyte27]

It was Ainslie's article that really changed my attitude about planning every dive, rather than a shoot from the hip approach. I do know divers taking AL40's on virtually every penetration. In a perfect world, where nothing else goes wrong, AL40's would work. Unfortunately, we don't dive in a perfect world.