Big Plans and Big Disappointment

[ScubaInChicago]

That's one hella of a walk to haul all your own gear without a support crew...

 

[ucfdiver]

Indeed. I also had the indignities of the worse possible vis in history in our dives in Seattle that we did as alternates and then a flight home.

Definitely good to see more examples of contingency planning for more complex cave dives.

Definitely I think helps once you start thinking of stages/doubles as "distance at a given depth" --- the planning makes more sense that way.

I think this type of planning needs to be introduced at the c2/full level. In low flow systems, 1/3rds isn't enough, and suggesting backing off by 100, 200, 300psi, etc is random and an uneducated decision at best.

At a certain point, you need to decide on a safety margin and realize what failures could kill you. Diving 1/3rds and believing nothing will happen is usually correct, but if you can't prove it from any reasonable failure in the dive, IMO it's not a well thought out plan.

 

[BabyDuck]

i'm sure someone will (& reasonably could) poke holes in your planning, but i appreciate your commentary on what you were thinking. i also think that there are only so many failures you can plan for at once before it gets silly & too 'little house'-y.

 

[rjack321]

I think this type of planning needs to be introduced at the c2/full level. In low flow systems, 1/3rds isn't enough, and suggesting backing off by 100, 200, 300psi, etc is random and an uneducated decision at best.

I've never thought of it as random. I've always thought of e.g. -200psi off thirds as a "percent slower".

E.g. for easy thinking, no stages, Al80 doubles... 1/3rds is 1000psi subtract 200psi is minus 1/5th of the third. Put 2 divers on those tanks at max penetration. 200psi of futz time at the OOA brings us to actual thirds (admittedly a fudge) now we can be 20% slower on the exit or use 20% more gas or a little bit of both (10% slower and 10% increased consumption)

Actually this isn't much different than thinking of the remaining gas (2/3rds plus 200psi) as a "distance at depth" or "speed at depth"

Minus 100psi only allows you to be 10% slower with an OOA at max pen., minus 300 allows for 30% slower exit. Gets a little more complicated with 3600psi fills but same concept applies.

 

[ucfdiver]

i'm sure someone will (& reasonably could) poke holes in your planning, but i appreciate your commentary on what you were thinking. i also think that there are only so many failures you can plan for at once before it gets silly & too 'little house'-y.

I'm open to discussing things, no offense taken if you had a comment on something :cool2:

I've never thought of it as random. I've always thought of e.g. -200psi off thirds as a "percent slower".

E.g. for easy thinking, no stages, Al80 doubles... 1/3rds is 1000psi subtract 200psi is minus 1/5th of the third. Put 2 divers on those tanks at max penetration. 200psi of futz time at the OOA brings us to actual thirds (admittedly a fudge) now we can be 20% slower on the exit or use 20% more gas or a little bit of both (10% slower and 10% increased consumption)

Actually this isn't much different than thinking of the remaining gas (2/3rds plus 200psi) as a "distance at depth" or "speed at depth"

Minus 100psi only allows you to be 10% slower with an OOA at max pen., minus 300 allows for 30% slower exit. Gets a little more complicated with 3600psi fills but same concept applies.

I guess. I like to think of things in time rather than %. If you have to patch a line, that takes 2-3 minutes at 20 or 300ft, same for entanglements, lost buddy drills, etc. If you have 5 hours of bottom time, a 20% reserve is an hour, more time than anything would take (aside from silt or slower dpv), but 20% on a 20minute dive doesn't leave much room for error, with a 4 minute cushion.

 

[Cave Diver]

This one is a bit long, I really debated posting it, but I think in this area of the forum it can be of some use, I would request that it not be copied anywhere because of the math it discusses. I suppose that if I don't post a dive report, I can't complain about only hearing reports on the grand traverse, bats, or godzilla circuit yet again.

Thanks for posting. Very interesting reading and the freedom to post numbers and planning is one of the advantages to having this forum.

I also really appreciated some of your reasoning, such as the examples listed below.

I swam here once and promised myself I'd never come back without a scooter...this is 100% scooter cave, as you can see by the sign, which prohibits swimming there!

Pfcaj was nice enough to loan me a second scooter for the dive, which was nice because I didn’t have to rent one…and it gave me someone else’s scooter for the further reaches of the cave, so if we had to lose one 10,000ft back, it wouldn’t be mine!

 

[rjack321]

I guess. I like to think of things in time rather than %. If you have to patch a line, that takes 2-3 minutes at 20 or 300ft, same for entanglements, lost buddy drills, etc. If you have 5 hours of bottom time, a 20% reserve is an hour, more time than anything would take (aside from silt or slower dpv), but 20% on a 20minute dive doesn't leave much room for error, with a 4 minute cushion.

I guess I have always thought that bigger dives needed progressingly larger cushions because there's "more" to go wrong. Not that all hell can't break loose on a short dive, but there's just less of everything to cascade out of control. Obviously still requires some common sense, let's scooter in 20mins to 1/3rds of a 1500psi fill puts you in a world of hurt regardless.

In any case I have always translated minus-X psi from 1/3rds into a % (time or speed) delay to make it relevant to me and put it in context.

 

[BabyDuck]

no, i didn't mean me - i have no experience planning something big like that dive, your stuff sounded good. i meant that your planning seemed reasonable and that even if someone had some holes to poke, once everyone has typhoid & there's a blizzard & the food's all gone, there's no way to plan for that.

 

[Dive-aholic]

I think this type of planning needs to be introduced at the c2/full level. In low flow systems, 1/3rds isn't enough, and suggesting backing off by 100, 200, 300psi, etc is random and an uneducated decision at best.

At a certain point, you need to decide on a safety margin and realize what failures could kill you. Diving 1/3rds and believing nothing will happen is usually correct, but if you can't prove it from any reasonable failure in the dive, IMO it's not a well thought out plan.

This is something I teach in my decompression courses and reiterate in my full cave courses. Planning is based on RMV, swim rate, volume matching, etc. It's enough for a non-stage, non-scooter dive. Planning for stage and/or scooter dives is a big part of the stage and scooter courses. While some will argue that this could/should be a part of cave training, there's already enough to deal with without adding in additional information that's not going to be absorbed as well. I do add some basic stage planning in my IANTD cave courses (since IANTD allows the use of a stage under specific circumstances).

 

[LiteHedded]

This is something I teach in my decompression courses and reiterate in my full cave courses. Planning is based on RMV, swim rate, volume matching, etc. It's enough for a non-stage, non-scooter dive. Planning for stage and/or scooter dives is a big part of the stage and scooter courses. While some will argue that this could/should be a part of cave training, there's already enough to deal with without adding in additional information that's not going to be absorbed as well. I do add some basic stage planning in my IANTD cave courses (since IANTD allows the use of a stage under specific circumstances).

meh you never know what you'll get with one of those.