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

[rjack321]

I am not cave certified and I am in no way looking for advice on how to perform cave dives. I always dive within the limits of my training and experience, and implore others to do the same. I am, however, very interested in cave diving, and I ask these questions as an intellectual exercise. If I ever reach this level of training, I'm sure this will be covered in classes, but in any case it will be many years from now, so I ask now to satisfy my nerdy curiosity...

In the latest video on BlueWorldTV, they dive in Jackson Blue and make a jump to a downstream passage off the main line. That immediately made me think about gas planning. I've read about strategies for diving downstream (siphons) using 1/6th of usable gas for the penetration, but what about dives with both upstream and downstream sections?

How would you approach gas planning on a dive like this?

- Recalculate when you get to the jump, so you use 1/6th of the remainder of your 1/3?
- Plan the whole dive at 1/6? Or an intermediate like 1/5?
- Other strategies?

You won't get an answer because "it depends". Apart from lots and lots of padding...

In some downstream passages the flow is so strong that you are in a delta-P situation and no matter how much gas you reserve you won't be able to exit and you die. Parallel lines isnt that small & fast but some places are.

JB's flow can vary significantly so you can't on the surface make some mathematical plan which will assuredly work in all situations either. In some flow regimes (esp with a big camera) just getting to their jump can take a 1/3rd of your available gas.

The "normal" way to plan a tourist swim like the one in the video is to talk to the locals about the flow conditions at the time, then come up with a reasonable 1/Xs amount of gas, Y distance, or Z time for the downstream section. Recalculate gas, distance, and time when you make the jump and turn around in the downstream section when one of those 3 turn markers is met. When you get back to the jump you should still have 2/3rds of the gas you used on the swim into that point/time. We way over emphasize turning gas here in SB, but really time is a huge factor in many cave turnarounds (if deco is accumulating) or distance can be a big factor too when flow is carrying you along and you exert barely any effort for the entry but may have a hard swim out.

e.g for the video dive

1. start with 3600psi in lp85s
2. swim in on 600psi
3. you have 3000psi at the jump minus 1200 is 1800psi usable
4. plan for 300psi downstream, 500psi return upstream, 1000psi reserve
5. you swim downstream and turn at 2700
6. takes you 600psi to swim back to the jump (harder swim than you thought)
7. arrive back at the jump with 2100psi
8. either recalculate again and head up the mainline and into the flow or exit that cave surfacing with 1500psi

Although to get to the jump to parallel lines in 600psi in lp85s would take a very low flow day in the first place (meaning going downstream wasnt a big deal), or an exceptional SAC rate.

 

[steinbil]

Thanks for the replies, everyone. Even though the thread took some twists and turns, and my questions might have been too simplistic, I have learned something. Thanks @grantctobin and @Jack Hammer for the good read, @tbone1004 for the description of the dive and honesty of a disputed practice, @rjack321 for the breakdown, @L13 for the support and @lostsheep for the popcorn.

My takeaways
- simple rules are too simplistic for complex diving
- thirds is not adequate for low flow or 2-person teams
- calculate the actual dive based on actual conditions, no shortcuts, use local knowledge
- you need a bigger reserve than you think when sh*t hits the fan
- i have much to learn

I’m looking forward to taking cave training in a few years (I hope), and until then I will continue to enjoy OW diving.

 

[L13]

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

Yes, a certified cave diver who doesn't know enough not to break that rule thinks he knows enough and doesn't think he needs to know more (or maybe he is right, and his detractors replace him as the ones who think they know but don"t). But, uncertified divers who know they don't know enough want to know more.

And some here think secret knowledge is the solution.

You are right, the irony is amazing

 

[kensuf]

There is no gas rule for siphons because different siphons will require more or less gas to exit.

In a spring, the rule of thirds really only works properly in a 3 person team or a high flow cave because the two non-OOG divers can split the workload of sharing gas with the OOG diver or the flow may help with the exit speed.

However, in a really high flow cave, the rule of thirds may not be sufficient in a 2 person team because really high flow can hinder your exit if you become entangled or snag on something; a friend and I did our best to kill each other when we got entangled in a line in a high flow cave several years ago. Big boy decisions.

Visual jumps are stupid. If you verified the circuit you can just set it up properly. Again, big boy decisions.

 

[L13]

Cave diver A:

I know! ​

The right way is X. Doing Y will get you killed. Only cave divers (who should already know this), should have access to cave diving knowledge.​

​

Cave diver B:

I know!​

The right way is Y. Doing X will get you killed. Only cave divers (who should already know this), should have access to cave diving knowledge.​

​

Diver C:

I know I don't know.​

Please give me knowledge about X and Y so that once I am certified I can be safe.​

​

Cave diver A and Cave diver B:

Heresy! The non-cave diver shall not be allowed to know The Secret Knowledge! ​

 

[lostsheep]

Because Mr Boomer above misunderstood my position, let me clarify.

I do favor sharing information on the forums despite the risk that something might be misunderstood, something subtle might be omitted, or an unqualified person might take the info and do something stupid with it.

That said, trusting someone on the internet to give you advice that might make the difference between life and death seems like a good way to win a Darwin Award.

WRT not maintaining a continuous guideline at all times, I don’t think that’s a very smart thing to do but I’d be lying if I said I’d never done it. On a related note, there’s been times when someone suggested we do visual jumps and I said absolutely not and I’m REALLY glad I did. I do not disagree that there are times the continuous guideline is debatable but I’m not going to pretend I’m not breaking a rule on some technicality. It’s a very real and unnecessary risk that is easy to avoid.

 

[berndo]

And some here think secret knowledge is the solution.

Information about gas planning for cave diving should not be shared on the internet. Should be pretty obvious why from just reading the opening post and seeing how much OP got wrong about what he thinks he knows.

I've read about strategies for diving downstream (siphons) using 1/6th of usable gas for the penetration, but what about dives with both upstream and downstream sections?

He read something on the internet or watched a youtube videos and think he's learned something. He didn't and the source was total horse manure but couldn't tell.
A lot of these cave diving videos do a massive disservice to cave diving as a whole.
Thinking there can be a gas rule for siphons is obviously nonsens.

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.

Yes, only trained cave divers should be allowed to know, because otherwise we have people that think they understand something (which they don't) go and kill themselves. Has happened more than once and people confuse random stuff they see and read on the internet with training.

A cave diver forum should probably restricted so only certified cave divers can read and post. There is zero upside in letting OW divers 'learn' about gas planing and cave diving techniques.

 

[PfcAJ]

Information about gas planning for cave diving should not be shared on the internet. Should be pretty obvious why from just reading the opening post and seeing how much OP got wrong about what he thinks he knows.

He read something on the internet or watched a youtube videos and think he's learned something. He didn't and the source was total horse manure but couldn't tell.
A lot of these cave diving videos do a massive disservice to cave diving as a whole.
Thinking there can be a gas rule for siphons is obviously nonsens.

Yes, only trained cave divers should be allowed to know, because otherwise we have people that think they understand something (which they don't) go and kill themselves. Has happened more than once and people confuse random stuff they see and read on the internet with training.

A cave diver forum should probably restricted so only certified cave divers can read and post. There is zero upside in letting OW divers 'learn' about gas planing and cave diving techniques.

That’s a load of trash.

 

[Wibble]

Information about gas planning for cave diving should not be shared on the internet. Should be pretty obvious why from just reading the opening post and seeing how much OP got wrong about what he thinks he knows.

He read something on the internet or watched a youtube videos and think he's learned something. He didn't and the source was total horse manure but couldn't tell.
A lot of these cave diving videos do a massive disservice to cave diving as a whole.
Thinking there can be a gas rule for siphons is obviously nonsens.

Yes, only trained cave divers should be allowed to know, because otherwise we have people that think they understand something (which they don't) go and kill themselves. Has happened more than once and people confuse random stuff they see and read on the internet with training.

A cave diver forum should probably restricted so only certified cave divers can read and post. There is zero upside in letting OW divers 'learn' about gas planing and cave diving techniques.

On the other hand, this is a place to learn and think.

Someone who comes here, reads these comments then immediately goes off to "plan" and then dive a complex -- or even simple -- overhead dive is violating Rule#1 of cave diving: GET TRAINED.

If they're stupid enough to ignore this, the ultimate penalty is death. Only the trained (and practiced) divers get cake.

 

[PfcAJ]

Information about gas planning for cave diving should not be shared on the internet. Should be pretty obvious why from just reading the opening post and seeing how much OP got wrong about what he thinks he knows.

He read something on the internet or watched a youtube videos and think he's learned something. He didn't and the source was total horse manure but couldn't tell.
A lot of these cave diving videos do a massive disservice to cave diving as a whole.
Thinking there can be a gas rule for siphons is obviously nonsens.

Yes, only trained cave divers should be allowed to know, because otherwise we have people that think they understand something (which they don't) go and kill themselves. Has happened more than once and people confuse random stuff they see and read on the internet with training.

A cave diver forum should probably restricted so only certified cave divers can read and post. There is zero upside in letting OW divers 'learn' about gas planing and cave diving techniques.

Thought police. Nice.