Gas planning and the associated math - controversies over need and how to teach

[NudeDiver]

How many folks driving down the highway do you think have planned their trip based on fuel consumption rates and fuel capacities? Their planning probably does not go much further than knowing, from experience, whether they will have to stop and get gas or not.

I have. When its several hundred miles between fuel stations (that are open), and it is cold and dark and icy, you need to plan this stuff out. Sometimes, you even have to stop for the night - not because you are tired, or because there are no hotels further on, but because if you keep driving, you will run out of gas before you get to the next gas station that is open.

Also comes into play if you are on a motorcycle and have a 3 gallon tank.

I see people on the side of the road, filling up their cars with a jug all the time. I've even been one of them - on several occasions.

Gas planning is important

 

[NudeDiver]

Running out of gas on scuba is not a life or death emergency either. You did have some plan for redundancy, didn't you??? If not, better take another look at golf.

If you have redundancy, then you didn't run out of gas. You merely ran out of gas in your primary tank. You have additional gas in another tank, whether your own or your buddy's.

 

[mikemill]

I know a university graduate who struggles with the basic math involved in calculating points during a game of dominoes.

Don't you know that the higher you go in math the worse your basic algebra becomes? Calculus, easy. Damn, making change requires some thought

 

[NudeDiver]

And standing beside the road waiting for the AAA to pitch up with a gas can to tie you over to reach the next gas station is not a life or death emergency, you could sit there safely all day if necessary

Around here it is. Try running out of gas 20 miles from anywhere, on a cold winter night when it is minus 50F outside (without windchill) - and by the way, AAA doesn't go there, and you have no cell phone reception anyway. Of course, being cold, dark and a crappy road, the next car to come by might not be until morning.

Same argument plays out in the middle of a hot desert too.

 

[AzAtty]

In our program, we strive to equip students with the basic knowledge to go out and find the answers for themselves, rather than being dependent on an instructor. By keeping someone dependent and spoon-feeding them answers, you are only hindering their intellectual and personal growth, whereas, we are hoping that they will come out of our program equipped to help themselves. This applies to all facets of life, not just scuba.

You should be burned at the stake with a fire fueled by the heretical writings from which you preach such doctrine. I am made physically ill to witness someone advocate such a sensible position.

I do not believe that it is a large extension of knowledge presented in OW to include SAC calculations, and certainly divers should understand basic gas planning. The fundamentals of the concept are presented in the basic physics and physiology sections. Students already learn that with "X" depth change, "Y" volume change results. Students learn that cylinder pressure is measure in PSI, and that cylinder pressure decreases as a student breathes from it. Students learn the working pressure of a cylinder and the volume of gas it holds.

SAC calculation is merely the assembly of these concepts to produce a new tool. Dare I suggest that is true "mastery" of a concept?

I disagree that SAC is a useless number. True, a new diver's SAC will vary. True, a gas plan will be inaccurate on something other than a square profile. But how does a diver know whether he can attempt a dive unless the diver knows how much gas it will require? "Be on board with 500 PSI" does not tell me whether I have enough gas to attempt a dive or manage problems, which are, IMHO, details I should know before I even bother packing my kit.

If instructors are concerned that the math is too complicated, then gas planning can be presented in broad terms such a cylinder generally lasting "X" minutes at a given depth. While the entire calculation need not be presented in exacting detail, the concept should be taught. The student should at least understand that s/he shouldn't attempt a 30 minute dive on 20 minutes of gas.

 

[don Francisco]

There's a difference between gas planning and gas management.

The car analogy is very apt. If you have a working gas gauge and open gas stations are everywhere, you can manage vs. plan fuel use. You decide to refil, for example, when down to a quarter tank and at that time stop at the next gas station. Perfectly fine for most normal driving situations and precisely what most of us do everyday. However you'd need more of a planning strategy when driving at night in sparsely populated areas. When gas stations are far apart it's important to know in advance that you have enough fuel to make it to the next station.

Carrying this over to diving, most people can be perfectly safe on most dives by managing vs planning their breathing gas. Not planning doesn't increase the likelihood of running short. You have a guage telling you what's remaining and when reaching your "low air limit" terminate the dive and head for the surface. Like with their cars, this is precisely what most folks do, and where it's workable it's perfectly reasonable.

Problem is that there are dives that don't allow for convenient termination at just anytime, for example a shore dive that extends out below a busy channel. In that situation it would be nice to be able to calculate in advance that your air supply will be adequate to complete the dive as planned, and not cause you to need to surface in traffic.

 

[MXGratefulDiver]

There's a difference between gas planning and gas management.

The car analogy is very apt. If you have a working gas gauge and open gas stations are everywhere, you can manage vs. plan fuel use. You decide to refil, for example, when down to a quarter tank and at time stop at the next gas station. Perfectly fine for most normal driving situations and precisely what most of us do everyday. However you'd need more of a planning strategy when driving at night in sparsely populated areas. When gas stations are far apart it's important to know in advance that you have enough fuel to make it to the next station.

Carrying this over to diving, most people can be perfectly safe on most dives by managing vs planning their breathing gas. Not planning doesn't increase the likelihood of running short. You have a guage telling you what's remaining and when reaching your "low air limit" terminate the dive and head for the surface. Like with their cars, this is precisely what most folks do, and where it's workable it's perfectly reasonable.

Problem is that there are dives that don't allow for convenient termination at just anytime, for example a shore dive that extends out below a busy channel. In that situation it would be nice to be able to calculate in advance that your air supply will be adequate to complete the dive as planned, and not cause you to need to surface in traffic.

Good points ... and a lot of how you look at this really does depend on the prevalent conditions you dive in.

Around here, one or two people end up dead every year because they ran out of air ... usually people who are attempting deeper dives without an understanding of how fast that gauge will drop at 100 feet (or deeper). Many of those people are fairly new divers with AOW certs who have been told that they're qualified for the dive that killed them ... most bolted for the surface when they took that last breath, and embolized before they got there.

... Bob (Grateful Diver)

 

[Thalassamania]

I've thought this over carefully and changed my mind. I might be willing to certify a student who was so math impaired that he or she could not do the calculations. I believe in custom built divers, hand-made, one at at time. Just as I have certified students who were comfortable in the water but who were not the world's greatest swimmers, I could see my way clear to do the same here if I felt that the they understood their impairment and had a clear plan for how to keep it from getting them in trouble. This might mean always diving with a much larger tank than their buddy, or always diving with a pony, or ... ? I'm not sure, but if I am faced with the situation (in something other than the hypothetical) I will handle it differently than I would have two days ago. Just how ... I'm not sure yet.

 

[Flightlead]

Again, Thal... the reasoning skills you're adding here are going beyond the level of most high-school graduates.

Oops. I sense a diatribe on how the high-school graduation standards have fallen over the last 50 years, and how that's leading to the downfall of the world.

Well I didn't have any problem teaching to my 11 yo step daughter who, frankly, is math challenged. Only one data point I admit, but I had no problem getting a girl that young, who could not tell time or make change, to understand and demonstrate that ability. Oh, and her ability to tell time, do math with time (base 60?), and make change all improved as well.

I just hope she's still diving where ever she is.

 

[Flightlead]

*raises hand*