Split from A&I Yukon thread: Gas Rules in OW Solo Dives

[FritzCat66]

My, hasn't the tone of this thread turned snarky. Why is everyone so determined to whack on SDI's teaching? And why will it matter because we'll all do what we darned well please, anyway?

I don't see it as snarkiness. I mean, SDI has already taken flak for being one of the only agencies to even offer a Solo cert, but I totally respect them for having the balls to do it. But that's not to say the course couldn't be improved, and while I am glad to have received the cert myself, I think the crticisms being brought up here are legitimate - especially the ones not necessarily criticising the use of the Rule of Thirds itself, but the rationale behind applying it to all solo dives.


Given that, I just looked through my SDI Solo training manual and it does not really provide that rationale, other than saying it's "wise".

Reviewing the SDI Solo training material, what struck me, however, is that I'm not sure the Rule of Thirds is taught as mandatory as some are interpreting it on this thread. Here are a couple of quotes germane to the issue (from the SDI Solo Diving Manual ©2007 TDI-SDI - note underlines are mine to emphasize my point):

"Rule Two: It's a wise diver who comes home... with one third their starting gas pressure in reserve... for the diver to deal with an emergency, such as getting lost, over-staying the NDL, or helping another diver..."

"While this practice may sound overly conservative to the average sport diver, it is... a great practice to adopt 'right out of the box'."

"We could of course work these calculations... to find out what volume of gas we are 'allowed' to spend on the dive: using the Rule of Thirds for example..."

"The Rule of Thirds is a basic planning tool for all overhead diving and as such is a good starting point for general gas planning for sport solo diving."

So, the manual says the Rule of Thirds is "wise", and a "great practice", and that we should use it as a "starting point" for gas planning, and there are several examples, review questions, and workbook problems that require the student to plan using the Rule of Thirds, but my takeaway from this kind of language is that it's a good rule of thumb, a good starting point, and certainly not a bad practice, but that, as a solo diver, ultimately it's my plan.


Contrast that kind of language with, for example, this from my Cavern training (from the NACD Cavern / Cave Diver Workbook, First Edition, ©2005 & 2006 NACD, again, underlines mine for emphasis):

"Cavern divers are limited to one-third penetration gas of a single diving cylinder..."

"Rule of Thirds - Failure to reserve at least two thirds of the starting gas... is the third most common cause of cavern and cave diving fatalities. This rule should be adjusted to a more conservative gas management plan under a variety of circumstances."

Unlike the Solo training manual, I really don't see a lot of qualifications and wiggle room here! Given this kind of language, my takeaway from the Cavern cert training - in contrast to the Solo cert training - is that the Rule of Thirds is an absolute starting point, the only deviation should be in situations where you would plan even more conservatively!

 

[DevonDiver]

Ok, thanks for the clarification - your side of the debate is clearer now.

It seems that the Solo course is a lot more vague than tech/wreck/cave courses. I always assumed that solo training would have an equally rigid doctine.

 

[Tortuga68]

First you're unhappy that they're enforcing rule of thirds for no good reason, now you're unhappy that they're not?

 

[Blackwood]

"The Rule of Thirds is a basic planning tool for all overhead diving and as such is a good starting point for general gas planning for sport solo diving."

Pretty much confirms my suspicions from page 1.

It seems more like they heard that cave divers do it so it must work.

Improper reasoning in my mind. YMMV (do whatcha want)

 

[HowardE]

I think the crticisms being brought up here are legitimate - especially the ones not necessarily criticising the use of the Rule of Thirds itself, but the rationale behind applying it to all solo dives.

I agree with you, somewhat. I'm philosophically opposed to calling something a "rule" since I find that rule implies ALWAYS, as akin to a scientific Law.

Personally, I think applying any "rule" to all dives of any kind is complacency. If you don't think about the situation you're diving, then you're not really planning at all - are you?

To me... having enough gas for the dive may be a complex set of mathematical equations, involving long deco times, buddies or not, penetrations or not, or what have you. If you want to rely on a crutch, like an arbitrary rule, then you may as well just do the 1000 psi rule or the 500 psi rule. Rules don't take into consideration the situation, which we as thinking individuals should do.

 

[Tortuga68]

I'm philosophically opposed to calling something a "rule" since I find that rule implies ALWAYS, as akin to a scientific Law

I don't think that's a good analogy. A scientific law is usually based on empiric observation, but is subject to change if further evidence proves it untrue

 

[Jax]

Perhaps more people should read the SDI Solo Diving Manual before they pass judgement. I, for one, found it well written in presenting good information, thought processes, and stressing on safety and responsibility for oneself. There was nothing that said, "thou shalt", "mandatory", or anything along those lines.

Instead, it says things like, "A properly equipped solo diver will wear the following: . . . ", ". . . one . . . thing to consider with regard to . . .", " . . . a good dive plan includes . . ."

The manual describes SDI's best practices. It is up to the diver (you know, that person that is responsible for him or herself), to take away what is important to this course.

Now, to pass the final cert dive, you do have to do a dive plan that includes you hitting the boat with one third of your gas, within the time allotted, shooting your SMB, etc . . . You have to show an understanding of what the course teaches. It doesn't come away with any "if you don't do this, you will die". [side note: My PADI nitrox instructor taught that if you break your MOD, you will die . . . ]

 

[lowviz]

Why on earth would that be at about 1000psi? Especially if you're diving solo and don't have to have gas for a buddy?
When did the rule of thirds become applicable to a no ceiling, open water diver?

Thalassaminia: At the expense of looking worse than PF, this thread pulled me out of lurking yet again. Won't happen again, promise. The rule of thirds is a simplistic approximation for cylinders at about 72cuft and above. The rule of thirds is inadequate for small cylinders. Gas planning is all about cuft (or liters). There are two procedures that make sense to me. Halves plus rockbottom and thirds plus rockbottom. The one you pick depends on the existence of a direct ascent. Realize, of course, that if you are going into deco then you must factor your hangs into the equation. The rockbottom calculation, for the diver in question, is a constant up to the point that the dive is turned. From then on, it is a variable. You can either feed your unused rockbottom credits into your exiting bottom time or just exit to the anchor line and, Duh, "lookit all the gas I have!", swim circles around the tie-in.

Plan the dive, dive the plan, burn your return credits on the interesting mental notes you made on the outswim and get back to the upline at your required ascent psi while never having violated rockbotton. -So easy even a New Jersey wreck diver can do it.

 

[HowardE]

I don't think that's a good analogy. A scientific law is usually based on empiric observation, but is subject to change if further evidence proves it untrue

Ok... how about a rule like a Legal Law? Either way. I don't necessarily subscribe to the concept of rules in a subjective environment.

 

[Jax]

Ok... how about a rule like a Legal Law? Either way. I don't necessarily subscribe to the concept of rules in a subjective environment.

Perhaps to consider a rule as in 'rule of thumb' or 'guide' or principal? I'm thinking "have 500psi when you climb on the boat" is one of those 'rules'. After all, we noobs need something to go on until we've built the experience.