Question Advanced gas planning for complex cave dive (upstream/downstream)

[happy-diver]

I feel fortunate that someone dared teach me English before I became a diver so I could learn along the way

The KISS mysteries of diver education, keep them stupid simple

 

[steinbil]

By "really" understand RB, I mean understand it's a) only as good as the assumptions you make and b) that you can apply it more than once. The point of RB in open water is you know you have enough to get you+buddy from where you are (the bottom) to somewhere else (the surface). Gee, what if you need to get back to the anchor before ascending? It's the same concept, although rather than depth, it's dependent on how far away you swim. With the assumption of no current and no difference in breathing rate on the shared return, it turns out RB is 2x what you used going away. This is precisely where the Rule of Thirds comes from. When you do it a second time like this, it's more commonly known as Modified Thirds (subtract off the ascent gas from what you have now and use 1/3 of the remainder to explore).

A good understanding of RB would also tell you that Thirds (Modified or otherwise) ain't going to cut it if the consumption rate changes or you're swimming into current on the return. However, you should also know how to modify your calculations to reflect those new assumptions. If it turns out you need 3x what you used going away, well that's (Modified) Fourths. Etc.

Nothing changes in a cave. It's all the same math as you would do for an open-water dive (assuming you want to ascend where you descended). Circling back, the takeaway should be gas planning is only as good as the assumptions you put into it. Hopefully that's enough to satisfy your inner nerd until you can discuss safe numbers for those assumptions with your cave instructor (someday, right!). In the meantime, plan your OW dives with Rock Bottom and Modified Thirds (or Fourths, Fifths, or Sixths) for excursions away from the anchor.

Thanks for detailed answer. Luckily this was part of my OW training, it's just called mingas and usable gas in GUE lingo. The nature of the diving I usually do around here often means "all usable" (but we always have mingas/rock bottom), although we often use halves when it's more convenient (but not required) to return to the entry point. I'm trained to calculate thirds on top of mingas for when you need to return, accounting for conditions like current.

 

[L13]

We must be thoughtful of not “teaching you how to think and calculate” gas planning. Many people will read this -who are not certified to be diving in a cave - and therefore should not be learning from us how to plan your gas.

How depressing that so many people think ignorance is a good safety principle.

If only certified cave divers are allowed to know something because partial knowledge is dangerous, then this forum would be pointless, since all certified cave divers should know everything.

The world if full of knowledge that can be dangerous if incomplete or misused, but gate keeping knowledge is a bad idea in every domain. "Keep the masses ignorant" is an insidious evil that infects many otherwise good people.

 

[Norwegian Cave Diver]

How depressing that so many people think ignorance is a good safety principle.

If only certified cave divers are allowed to know something because partial knowledge is dangerous, then this forum would be pointless, since all certified cave divers should know everything.

The world if full of knowledge that can be dangerous if incomplete or misused, but gate keeping knowledge is a bad idea in every domain. "Keep the masses ignorant" is an insidious evil that infects many otherwise good people.

The OP states he/she isn’t cave certified. If that would be different then the entire post would be a completely different. We would be having a hearty discussion on how to manage your gas with and without a stage etc. Diving in open water is entirely different that diving in a cave. In open water you can be at 100 feet and be on the surface in 3-4 minutes. But in a cave when something goes wrong could easily mean you have a 1+ hours of swimming to get to your exit.

Cave training is extensive and far beyond just gas management.

It is an easy place to make a mistake and be dead just not know it yet.

It is unfair of you to criticize me for withholding that information to a non cave certified diver.

 

[steinbil]

The OP states he/she isn’t cave certified. If that would be different then the entire post would be a completely different. We would be having a hearty discussion on how to manage your gas with and without a stage etc. Diving in open water is entirely different that diving in a cave. In open water you can be at 100 feet and be on the surface in 3-4 minutes. But in a cave when something goes wrong could easily mean you have a 1+ hours of swimming to get to your exit.

Cave training is extensive and far beyond just gas management.

It is an easy place to make a mistake and be dead just not know it yet.

It is unfair of you to criticize me for withholding that information to a non cave certified diver.

I think I also made it pretty clear that I had no intention of ever diving beyond my training. To follow your example, I could have easily lied about (or withheld) the information about my certification status. And what if I as an non-cave diver reads a similar thread made by a certified cave diver? If this is indeed the intention, then the forum should only be accessible to certified cave divers. At the very least, there should be forum rules about what could be discussed.

I'm not certain that withholding knowledge is the best policy. In my case it wouldn't really matter either way, as I respect the limits of my training. For the reckless divers, I'm not sure withholding that information will stop them. Maybe there is a contingency of internet-educated divers on the fence that would get the "last piece of the puzzle" and feel competent to execute these dives without training. I'm sure there are people smarter than me with more experience that have given this more thought, so as I said I would defer to the community on this.

 

[Wibble]

The OP states he/she isn’t cave certified. If that would be different then the entire post would be a completely different. We would be having a hearty discussion on how to manage your gas with and without a stage etc. Diving in open water is entirely different that diving in a cave. In open water you can be at 100 feet and be on the surface in 3-4 minutes. But in a cave when something goes wrong could easily mean you have a 1+ hours of swimming to get to your exit.

Cave training is extensive and far beyond just gas management.

It is an easy place to make a mistake and be dead just not know it yet.

It is unfair of you to criticize me for withholding that information to a non cave certified diver.

Diving in Open Water means you need enough gas to get you to the surface when ONE FAILURE has occurred. This means for a simple deco dive:

• should your backgas fail, you must be able to save some gas by shutting down a cylinder
• should your deco gas fail you must be able to complete the dive on backgas alone

For deeper/longer dives this means that you will carry two (or more) deco gasses and you must similarly cater for one failing and be able to run the deco on only one deco gas.

Planning for CCR's the same: bailout must be sufficient to cope with the time you've had on the bottom when the rebreather catastrophically fails. More often than not, the amount of bailout you can carry is the limiting factor for dive duration.

Cave diving on CCR is not much different. You must have sufficient bailout to cope with the CCR failure and get out alive.


For ALL of the above, you need to know your SAC and do some basic maffs to ensure there's enough gas in reserve.

 

[L13]

The OP states he/she isn’t cave certified. If that would be different then the entire post would be a completely different. We would be having a hearty discussion on how to manage your gas with and without a stage etc.

So the knowledge is secret, unless one claims to know the secret handshake? then it is given freely even though it is readable by the world? Isn't that a bit irrational?

But in a cave when something goes wrong could easily mean you have a 1+ hours of swimming to get to your exit.

Has nothing to do with whether knowledge should be kept secret. Actually, I think it is a better argument for sharing knowledge.

Cave training is extensive and far beyond just gas management.

Maybe, but depending on the teachers involved, some cave training will be far more extensive than others. You have no idea what any particular persons training is, regardless of whether the claim a cave cert or not.

It is an easy place to make a mistake and be dead just not know it yet.

Which is exactly why knowledge should be actively disseminated, not secretly hoarded.

It is unfair of you to criticize me for withholding that information to a non cave certified diver.

Actually, it is perfectly fair for me to criticize the behavior. It is a fundamentally flawed philosophy.

 

[lermontov]

I'll say it because no one else will. The way this is typically dove if you plan on going past where // pops back out is that divers will blind jump into // lines because through most of the passage you can actually see and get back onto the gold line every 30-50ft or so, then blind jump back onto the gold line and carry on until they hit turn pressure and coast out on the gold line. The slightly less bad way is to jump into // and blind jump back onto the gold line but you should verify said gold line if you're going to do that knowing that it's not the way you're supposed to do it. If you've verified it though it still maintains a continuous guideline to the exit.

why blind jump - i thought this was the antithesis of cave diving practice

 

[lostsheep]

We have two posters arguing about whether or not info should be shared publicly plus one guy suggesting breaking one of the fundamental rules of cave diving all in the same thread. The irony is amazing

I think I’ll just sit back and watch the show.

Someone pass the

 

[Eastman]

We have two posters arguing about whether or not info should be shared publicly plus one guy suggesting breaking one of the fundamental rules of cave diving all in the same thread. The irony is amazing

I think I’ll just sit back and watch the show.

Someone pass the

Although the person suggesting breaking one of the fundamental rules of cave diving is a cave diver himself, making your point fairly moot.

People are going to do what they do, no matter what cert they have. Knowledge should never be withheld.