Survey question rebreathers

[Superlyte27]

I was looking for an example of how you (Jason) would plan for a failure: gas, time, etc.
Bob

Florida...
I don't think he's a CCR diver. I could be wrong, but that's probably why he doesn't have examples.

[H2Ocaver]

Take this a step farther, if you are doing 10k at 100'-you are going to do a setup dive and clean up on the way out. That becomes a 6k dive and a second dive past 6k. Assuming that a dive that far will be at least partially in a spring (not a siphon). This increases safety and lessens the unknown cave conditions that would turn the dive early. If trying to go 10k by just dropping the tailgate and jumping in, that's not safe to begin with, even if you planned to carry a bunch of BO gas. A safe way to plan for gas at this point would be to put one AL80 every 2k in up to 6k on a setup dive and then everyone carries 2 AL80's up to 8k. then the team decides if conditions warrant an 8k drop or run the rest of the way with both 80' on each diver. That's 9 al80's
(3 man team carry 2 each and one at 2k, one at 4k, and one at 6k) with 720 cft of gas, and at an expected exit at 50 per minute there would be about 640 cft of gas ( at .8 sac) used by one diver swimming out from max p'. This also puts the multiplier up against reg failures and distance needed to swim to fresh gas. Also, the fact that there would be four scooters lessens the likelihood of swimming total distance. The setup dive could be done with each diver carrying only one 80 to drop. of the two they would use for the dive and even at 6k there would be the other two 80's on the floor on the way out. This is what I would do as a minimum of BO gas and dive prep/planning.

I chuckled a little when I found out what Odin's real name is.

So, last week I planned a scooter dive to the far end of a cave. The goal was 10k' I plan my bailout pretty much the same all the time. How long will it take me to swim out? I'm assuming my CCR is going to die, my scooter crapped out, and my buddy didn't notice and kept on scootering, leaving me alone in a cave. I was teased a bit for this approach when we started planning our dive.

So, how much gas would you bring to a cave dive with an average depth around 100' back 10,000'. It was three divers, all CCR. 4 Scooter. My dive buddies wanted to bring 2 AL80's each. Sure, if we all brought AL80's that would be 464.6cu' split between 3 people. But what if I lost my buddies, will 155cu' get me out of a dive 10k back? Sure, maybe, if I had perfect breathing, no anxiety, and nothing else went wrong.

Imagine, swimming 10k'. What pace can you keep up? 80fpm? That's 125 minutes. What's your gas consumption going to be? You're all alone in a dark cave, your scooter and rebreather have just taken a crap. Can you maintain a .5sac? I don't think so, but who knows. Let's assume a .6 sac. So lets figure .6 x 3.73ata x 125 minutes = 280cu'. And frankly, I don't believe you can maintain both 80' per minute because of the winding/up & down nature of the cave and a .6sac rate. So for me, I think it's more realistic to calculate 75pfm and a .75 sac rate. Remember, who knows how bad things got when scooter and rebreather got screwed up, how long is it going to take you to gain composure? So, now we're at .75 x 3.73 x 133 = 372cu' of gas.

Sure, this is assuming several things went wrong. And I agree, 99 out of 100 times, you're not going to have both things die and you lose your buddy. But what happens that 1 out of 100 times? I don't ever want to count on my buddy to survive. I also don't ever want to count on my one scooter to survive. I'm just not that trusting. And the peice of mind that comes with enough gas to swim out makes for stress free diving.

That's my perspective anyway.

[Greenwood_60]

Peter is correct, I'm not a CCR diver. Bob know that though. My point was thinking about it only from only a quantity of gas point of view was wrong, ccr or oc. Peter's is a perfect example. Multiple things can go very wrong and he'll still have the gas at hand to survive.

[PfcAJ]

Take this a step farther, if you are doing 10k at 100'-you are going to do a setup dive and clean up on the way out. That becomes a 6k dive and a second dive past 6k. Assuming that a dive that far will be at least partially in a spring (not a siphon). This increases safety and lessens the unknown cave conditions that would turn the dive early. If trying to go 10k by just dropping the tailgate and jumping in, that's not safe to begin with, even if you planned to carry a bunch of BO gas. A safe way to plan for gas at this point would be to put one AL80 every 2k in up to 6k on a setup dive and then everyone carries 2 AL80's up to 8k. then the team decides if conditions warrant an 8k drop or run the rest of the way with both 80' on each diver. That's 9 al80's
(3 man team carry 2 each and one at 2k, one at 4k, and one at 6k) with 720 cft of gas, and at an expected exit at 50 per minute there would be about 640 cft of gas ( at .8 sac) used by one diver swimming out from max p'. This also puts the multiplier up against reg failures and distance needed to swim to fresh gas. Also, the fact that there would be four scooters lessens the likelihood of swimming total distance. The setup dive could be done with each diver carrying only one 80 to drop. of the two they would use for the dive and even at 6k there would be the other two 80's on the floor on the way out. This is what I would do as a minimum of BO gas and dive prep/planning.

Really overcomplicating it.

This dive (especially if it's where I think it is) is a thing you can do safely on OC with less effort than you're describing.

But sure, by all means go nuts.

[H2Ocaver]

If this is too complicated, may I suggest golf?


It's a setup dive and a 10k dive w/clean up. 32 thousand feet of cave diving in two dives and the most effort is that everyone carry a third stage on the way out.
Unless you just want to drop a glory marker and run out, that is a lot of cave to just zoom by and not appreciate.
But, I'll just go nuts.
It would be easier if I was an Eagle scout.

Really overcomplicating it.

This dive (especially if it's where I think it is) is a thing you can do safely on OC with less effort than you're describing.

But sure, by all means go nuts.

[PfcAJ]

An Eagle Scout would probably bring even more stuff

IMO if you place a priority on propulsion (towed scooters, switched at a reasonable interval) it's reasonable to do a 10k dive without a setup/a bunch of safety bottles dropped along the way.

Whenever I longer scooter dives, I put enough scooters in the water so that swimming out isnt really needed unless an absurd amount of stuff breaks. With a good buddy, you'd have to lose 4 scooters before you're swimming.

Everyone does it differently I suppose.

[FW]

An Eagle Scout would probably bring even more stuff

IMO if you place a priority on propulsion (towed scooters, switched at a reasonable interval) it's reasonable to do a 10k dive without a setup/a bunch of safety bottles dropped along the way.

Whenever I longer scooter dives, I put enough scooters in the water so that swimming out isnt really needed unless an absurd amount of stuff breaks. With a good buddy, you'd have to lose 4 scooters before you're swimming.

Everyone does it differently I suppose.

A lot depends on whether you have extra scooters, or extra tanks to stage

[Superlyte27]

Really overcomplicating it.

This dive (especially if it's where I think it is) is a thing you can do safely on OC with less effort than you're describing.

But sure, by all means go nuts.

It was pretty simple for me. I sidemounted LP108's and tail dragged a AL80. That's just about 370cu' I dropped the 80 on the way in.

-edit-
I only own one scooter. Two scooters would allow me to plan differently.

[nakatomi]

I only own one scooter. Two scooters would allow me to plan differently.

I've never had a serious/catastrophic gas failure that made (all) my gas inaccessible, nor do I know anyone who had this happen.
However in my measly 50 DPV cave dives so far, I already had two scooter failures that forced me to swim out.
Clearly in both cases it was more or less my fault, but it still happened.

Based on the chances of tanks vs. scooters failing, I'd personally prefer redundant OC reserves/bailout over backup scooters any day.
One bad charger can screw up a charge for N scooters. Scooters are much more likely to fail than a simple tank with a valve.

[PfcAJ]

I always view scooters as the most suspect, and ive had a few failures myself but never to the point of having to swim out.

My suspicion of them makes me tend to plan a bit more "scooter heavy" than others.