Mix choice

[Superlyte27]

Rjack, it was a joke and a shameless plug for my favorite shop, nothing more. Try not to take it too literally

 

[rjack321]

Generally, air in an area in which trimix is too costly or not available. Or, the dive might not pan out and you are burning an expensive fill. Air is "good" to 130 according to cave diving standards for END and it definitely has greater range if needed.

Air is worthless if you want a decent survey at any kind of depth. This is above and beyond any consideration of entanglements, silt on the floor or having to crawl through silt, percolation, blah blah. The realistic range for good survey data on air is about 50ft...

From what you describe, I'd say you are right with the 25/25 or 21/35. But, if you want to split the difference use 18/55 (boost helium a bit beyond the DIR standard gas content) because it's a 200 foot gas extended to 220 if you wanted to increase the PPO2 to 1.4 ATA. A Nitrox32 top-up around 1400 psi will give you the UTD standard gas of 25/25 which can be used at 140 - 150 feet at ppO2's of 1.3 and 1.4 ATA. A rock bottom plan should keep more gas in the tanks from which to top and keep the gases close to "standard" mixes for remaining dives. You can still get a third dive in the range of 28/11 with another Nitrox32 top-up to take the edge off a 120 - 130 foot dive.

Sure I could bring a compressor (I even have one). I have 3 sets of suitable SM tanks right now so though so filling in the field is a waste of time. What I don't have is the luxury of multiple sherpa days getting tanks down and back out of a cave.

 

[ucfdiver]

18/45 always

18/45 doesn't go real far if he's limited to Hp100s.

If you're only going to use o2 deco, I would say that's the limiting factor, stick with 21/35. You can't go much below 150ft in a cave and still maintain rock bottom with only one deco gas any ways-- unless it goes deep fast and you don't burn gas getting to the deep section.

 

[LiteHedded]

Rock bottom? C'mon...
Ur gonna plan yourself out of a dive.

 

[Dive-aholic]

21% O2 so I could get down to 185 if needed and the least amount of helium you are comfortable with at the MOD of the O2. For me it would be 35% helium. If you feel you need a little more for survey then boost it up, but keep in mind that this will increase you decompression obligation. You may want to sacrifice one for the other.

 

[rjack321]

18/45 doesn't go real far if he's limited to Hp100s.

If you're only going to use o2 deco, I would say that's the limiting factor, stick with 21/35. You can't go much below 150ft in a cave and still maintain rock bottom with only one deco gas any ways-- unless it goes deep fast and you don't burn gas getting to the deep section.

I don't realistically have a way to get bigger tanks down there. Unless they are full of helium and just drift down with the draft

Rock bottom? C'mon...
Ur gonna plan yourself out of a dive.

LOL you think 140ish was just plucked outa thin air?

 

[LiteHedded]

i mean, you're controlling that deco obligation. not the gas. the difference between 18/45 and 21/35, deco-wise, isn't even worth discussing on an exposure like this.
but if 140 is your max there's no harm and dialing it back some. I'm interested to hear how it shakes out and what you find there

 

[rjack321]

i mean, you're controlling that deco obligation. not the gas. the difference between 18/45 and 21/35, deco-wise, isn't even worth discussing on an exposure like this.
but if 140 is your max there's no harm and dialing it back some. I'm interested to hear how it shakes out and what you find there

I'm considering splitting up my double 95s/119s (I have a set of each) this gives me a little more range and if I'm lucky the sherpas won't notice the extra size & weight... I'm not really a solo kinda guy, but there's nobody else willing and interested in diving stuff like this around here. So the 140-150ft max isn't a hard limit, its more of a common sense/psychological decision not to hang myself way out there by myself, hours and hours from anywhere, just for a cave.

But for all I know, the cave piddles along at 20ft in a nice clean tube before spitting me out in the ocean!

 

[Dive-aholic]

i mean, you're controlling that deco obligation. not the gas. the difference between 18/45 and 21/35, deco-wise, isn't even worth discussing on an exposure like this.
but if 140 is your max there's no harm and dialing it back some. I'm interested to hear how it shakes out and what you find there

Really? Based on no O2 and a max depth of 140, the difference between 18/45 and 21/35 is 19 minutes of cold decompression time. I think that's worth discussing.

 

[LiteHedded]

what bottom time? what algorithm? how much time at 140? let's pick a realistic profile here...