So, this stuff isn't supposed to happen, but I guess it does

[PhatD1ver]

Good stuff folks!! thanks for the pearls...

I'm just off to California next week to see how much cold water affects me... brrr (actually, I think I am half penguin, I love the rush of a cold water thermocline when I run into it... a little bit of a shock maybe, but feels awesome)...

Lucky for me the dive shop in San Pedro has steel 95s, that ought to help a little... going to be a lot going on, I'm going to be on my best situational awareness behavior.

 

[Storker]

So, as a 'responsible' and 'courteous' diver, isn't it MY problem to resolve? And if it means I have to carry a slightly higher capacity cylyinder, and recheck my weighting, I fail to see what is wrong with that? I'm still going to have to plan by 1/3s, I am not learning any bad habits, I still am going to have to plan to ascend and begin my safety stop by 70bar, that puts me on the surface with a reserve of 50bar in the tank. admittedly, it won't be a perfect 1/3 rule. But it is responsible planning.

Rule of thirds is a method of gas planning, and gas planning is always good. However, I don't think that the rule of thirds is very good gas planning for a rec dive. You might want to read up on "minimum gas" or "rock bottom"; NWGratefuldiver here has written a good article on that (if you're imperial, that is. It's not that well suited for us metric guys).

AFAIK, an HP100 has a fill pressure of 3440 psi (almost 240 bar), which should give it a water volume of about 12L. With my SAC rate (~0.5 cuf/min) and a 12L 240 bar tank, the rule of thirds overestimates the required gas reserve at depths shallower than about 18m/60ft (which is good, since it gives you an extra safety margin) and underestimates it at depths below that (which is bad if fit hits the shan). With a higher SAC rate, the rule of thirds is even worse; if your SAC rate is ~0.7 cuf/min, rule of thirds gives you a correct estimate as shallow as around 12m/40ft.

And the error becomes bigger the deeper you go, so if you're planning to dive deeper than 18m/60ft, you should seriously consider to read up on more advanced gas planning. It's not rocket science, it's just a little math.

 

[Tony387]

Monitoring you air is both the most basic and most important skill a new diver needs to learn. If you're running out of gas you're not paying sufficient attention to what you're doing or diving profiles beyond your skill level, or both.

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