Stage planning in caves

[RTodd]

Let's say that you were doing a dive in Madison Blue (no scooters). Would you double stage it, and go to 1/3's on backgas, or would you only stage the 80's and not touch the backgas?

Assuming that you are staging 80's, and diving 1/2+200, you would use approx 70cf of gas. Now a set of 120's run at thirds would give you 80cf of gas, without the drag of the stages.

I guess my question is, on a double stage dive if you're not going to touch your backgas, would it not be more efficient to dive the doubles to 1/3's instead of staging?

Thanks

You get these nonsensical results in theory only. This is partially in answer to the question below too.

First, a double stage in Madison isn't a very good idea. That puts you with two stages going through crossover or one through rocky horror. So, I would single to Rocky Horror, dive the stage to halves and then use about 1/4 of total gas if it was a squared away team that could quickly exit that cave in a gas share.

You need extra gas on scooters and stages usually = scooters. So, two stages and full back tanks that don't get touched on a scooter dive which allows you to cover much greater distance and allows your SAC rate to stay much lower than swimming makes perfect sense to me.

There is nothing wrong with having too much gas. Now, a simple swim dive where the objective can be reached on back tanks to thirds. Probably wouldn't bother with stages in the first place because you cover much more distance without them swimming.

 

[rjack321]

don't personally do anything remotely on this scale, so can't really comment definatevely on where the line is. They did use open circuit out past 10k feet in Wakulla. Not many caves of this magnitude and depth. Also, keep in mind that a .5 SAC rate even completely stressed is unlikely for divers at this level and that few caves have an actual average depth of 10ATA. So, you are looking at more like 10+ minutes of trigger time and some stage changes are done mostly on the fly. Having dived with some of these guys when they were doing this open circuit and had the get it done fast attitude, I can tell you that causing the team to spend 2 minutes on a stage drop would cause you to catch an enormous amount of grief. I used to wait ready to go at drops with Danny and Chris thinking what is taking these guys so long. Now that I have the take your time and be careful attitude of stage drops more appropriate to Mexico, they are back to waiting on me since my ability to do the drops carefully is slower than theirs.

LOL Lamont and I have our SACs in the 0.5 neighborhood completely relaxed! Although when the water is warmer than 55F mind you I can get into the low 0.4? range. I have yet to do a dive with it below 0.40 even in MX.

Thanks for the primer on stage usage at the Cave2+ level, it is helpful to bone up on these planning/mathematical exercises to free up class bandwidth for other complexities.

 

[do it easy]

Also, keep in mind that a .5 SAC rate even completely stressed is unlikely for divers at this level and that few caves have an actual average depth of 10ATA.

Just curious, what kind of SACs are we talking about? What do divers are this level use for gas planning purposes?

I know to some extent that SAC is dependant on the individual, but what would you consider a decent SAC rate for a "world class" explorer?

 

[Mike Edmonston]

Just curious, what kind of SACs are we talking about? What do divers are this level use for gas planning purposes?

I know to some extent that SAC is dependant on the individual, but what would you consider a decent SAC rate for a "world class" explorer?

World class explorer, I AM NOT! But when I am on a true exploration dive, (tight caves, looking for passages etc...) my sac rate really sucks (pun intended). The workload, and excitement trump ANY semblance of a descent sac rate.

YMMV

 

[rjack321]

Just curious, what kind of SACs are we talking about? What do divers are this level use for gas planning purposes?

I know to some extent that SAC is dependant on the individual, but what would you consider a decent SAC rate for a "world class" explorer?

I think what Rtodd was getting at is that the "world class" don't have highly elevated SACs when stressed. So their "normal" 0.22 to 0.25 (which is about what Danny Riordan's is) goes to a whooping 0.3 when stressed. Vs. the rest of us mortals who can't even dream of 3 hrs and 6000ft of swimming (albit at 25ft) on a single set of AL80s and finishing with 1400psi.

 

[do it easy]

Thanks- that helps. I was trying to get an idea of how low it can get and what kinds on numbers are used for planning.

 

[SparticleBrane]

Sheesh I thought my SAC at 0.48-0.5 was decent. :11:

 

[Doc Intrepid]

Heh...I'm delighted just to be breathing each morning when I wake up.

My SAC rate inside caves is probably .8 or so...I don't know, I never measured it. I was too busy trying to not freak out and pull some bonehead move that would silt the place out...

 

[coldsmoke]

I've noticed that I sometimes get minor headaches after dives. I searched here and the other boards to see if I could find a reason and read somewhere that it could be due to low SAC rates. I don't remember where I found it, but basically it was because of less than ideal CO2 expulsion. Anyway, I went back through my wetnotes (this is where I keep a dive log so to speak - not much, just gas used, time, depth, avg depth, etc.) and the dives that I remembered having headaches were dives with lower than normal SAC rates for me. My normal is between .4 and .5, usually a little closer to .5. And the ones I could remember that I had headaches were high .3's very low .4's. I don't have a lot of reliable data on this so my conclusion may be entirely coincidental.

Seeing the SAC rates above, obviously, low SAC rates can't be the answer. Perhaps if your SAC rate is lower because you are consciously trying to reduce consumption, but that wasn't the case with me and I'm sure it's not the case with those mentioned above.

Kinda off on a tangent, but seeing others with such low SAC rates got me thinking that what I thought was causing the headaches might not be. Anyone have any ideas?

Thanks.

Hunter

 

[TSandM]

It's a little off topic, but I think you are entirely right to think it's CO2 retention.

The SAC rates of people like Danny are not achieved by underbreathing, but by an EXTREME efficiency of movement (Danny never moves any part of his body that doesn't directly contribute to what he wants to do in the cave), absolute stability, relaxation, and an inhuman degree of fitness.