My hose setup, am I close?

[MXGratefulDiver]

Not sure you guys got Kevin's point.

There is NOT a 50/50 chance of having more than enough gas. If you dive by the rules, you will always have more than enough gas.

Worst case, you are down to a third in each tank. You suffer a catastrophic loss in one tank.

However, if you are down to a third, you are at your exit. A third of one tank AT your exit is more than enough gas.

Now, interpolate that to any point in the dive ... If you practice good gas management, you will have more than enough gas.

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Well ... not necessarily. If you're diving thirds, you turn on 1/3rd ... so let's say you lose one cylinder at just exactly the worst time ... right at your turn pressure. You've used 1/3rd out of each cylinder. You have 2/3rds left in each. You lose one ... you now have the other to get out.

You've just lost (overall) your 1/3rd total reserve ... and you have exactly the same amount of gas to breathe going out as you used going in ... you just have it in one tank instead of two.

Moral of the story? Don't breathe either tank below 1/3rd before turning ... there's no 50/50 about it ...

... Bob (Grateful Diver)

 

[Jax]

Well ... not necessarily. If you're diving thirds, you turn on 1/3rd ... so let's say you lose one cylinder at just exactly the worst time ... right at your turn pressure. You've used 1/3rd out of each cylinder. You have 2/3rds left in each. You lose one ... you now have the other to get out.

You've just lost (overall) your 1/3rd total reserve ... and you have exactly the same amount of gas to breathe going out as you used going in ... you just have it in one tank instead of two.

Moral of the story? Don't breathe either tank below 1/3rd before turning ... there's no 50/50 about it ...

... Bob (Grateful Diver)

Okay, assuming one calculates to the nth degree. However, everyone I chat with has a few hundred in there they don't count in the calculations of thirds. Some say "turn 200psi short of 1/3", others just shave off some psi before calculating thirds. . . bottom line, it would take one hell of a catastrophe to bring the people I know of to empty at the end. Oh, and that isn't even counting in the buddy's long hose. (or pony)

EDIT - - - - Oh, looky, I brought it back on topic. ^ ^ ^

 

[FWADIVER]

sorry everyone misunderstood what i was saying, lake county diver got it right, your have a 50% chance that rule of thirds works in your favor, 2 tanks, assuming total gas failure (tank oring extrude) depending on which tank it was, even at worst case 1/3 turn pressure one take will have more air than the other. I am not advocating rule of thirds, but it is the least conservative option, which should leave you with just enough gas to make it to your stage/deco tanks, not saying its ideal, but its better than if you had manifolded doubles imho. (oring extrude causes gas loss from both cylinders before you can isolate, and then you can only use one cylinder after that). that also assumes its not something like a first stage failure where you can use the gas by feathering, or switching regs... just pointing out how the math supports not needing a long hose if diving a sidemount only team. As i posted above, i use one for peace of mind, but I can understand the opinion of guys that use short only. I really dont want to de-rail this any further with gas management and what is ideal for conservative enough, it was more a discussion on why people use certain hose setups for sidemount.