For our dive-date yesterday Nelly and I went to a favorite cenote we don’t visit nearly as often as we should with the plan of checking out as many of the jumps off the mainline as we could.
For those of you not familiar, the most typical way to plan safe gas reserves is by applying “the rule of thirds,” where you plan to use one third for linear penetration, assuming no change in conditions or problems you use one third to come home, and have one third in reserve. Linear penetration being the key to this plan… one way in, one way out.
But that’s not what Nelly and I were doing yesterday. Instead of following a single line in, then out, we were gong this way, then that way, then over here, then over there (and in some cases finding that we had looped back around on ourselves).
To do this one employs a bit of quick, and fairly simple, arithmetic referred to as “recalculating thirds.” That is: you take stock of exactly where you are in the cave, how much gas you have left, and determine what you will need as a team to safely exit if things go pear-shaped. It needs to be done every time you change direction and requires extreme situational awareness.
I was going to write this morning about the way that I do and teach this skill. I figured it might be a fun way to hear about how it compared to the way other people might think about it or teach it or apply the math.
Until late last night as I was trying to fall asleep when it occurred to me that was a terrible idea.
I started thinking about how dangerous it can be when people have only part of the picture. Especially when it’s part of a vital safety protocol that requires a direct action application of a theory. Recalculation is something taught in the classroom (typically at the Full Cave level), reviewed at the dive site, practiced in the water, debriefed, and repeated several times.
I thought about the accident reports of people who followed DMs through a shipwreck who thought they could navigate the same dive on their own. I thought about all the message board posts where some keyboard warrior is adamant about where to stow some piece of gear… but obviously doesn’t even understand why they’re carrying it. I thought about the number of people who decide to just start carrying a stage or riding a DPV or going into light deco because their one friend who knows a guy who took a class said it’s no big deal.
I thought about a time I heard (with some horror) about my own student, who had listened to my own, in-person, impassioned lecture about normalization of deviance going on to dive past their training limits.
I thought about how I don’t want to ever hear about how someone used some goofy FB post of mine as instructions on how to plan a complex dive and got in over their heads. Or worse.
Basically, I remembered the adage: a little knowledge is dangerous thing.
So that’s what I wound up writing about instead.
Learn things properly, thoroughly. Look for holistic answers. Focus on and explore details, but don’t be satisfied with only part of the picture. Find instructors and mentors you vibe with and parse things out with them. Have them watching your back while you try advanced techniques for the first couple of times.
And, for the love of god, don’t plan dives based on some shit you read on the internet.