Tank size and air consumption

[RN]

Rob, I'm interested on your gas plan and gas switch thoughts in that configuration.

It really depends on the cave and the dive, Larry. Just like I teach in my stage classes, whether you use 1/2+200 or 1/3s in your stage will depend on the dive you're doing. My choice depends on whether I'm scootering or swimming, where I will be putting my stage cylinder once I take it off, and what kind of navigation I'll be doing in the cave. It also depends on the sidemount cylinders I'm using. With all AL80s I do something different as well.

[DA Aquamaster]

Thanks Rob, it sounds like what we're doing is in the right ballpark as we tailor the plans to the dives and not be locked into any single method. It's the diving with 3 more or less equal sized tanks in SM that promoted the question.

[SuPrBuGmAn]

I do get longer dives out of LP95s(and the HP130s before that), however my wing is inflated more and there is (barely) an increase in tank diameter and drag. If I can get away with diving 72s, I will.

Hell, if I can get away with diving 40s, I will.


I don't WANT to carry heavy tanks.

[aquadog196]

If you're diving the tanks to 1/3rds then 1/3rds is 1/3rds ..no additional reserve gas regardless of tank size.

[PfcAJ]

Thirds of 85s does not equal thirds of 104s...

[a64pilot]

If you're diving the tanks to 1/3rds then 1/3rds is 1/3rds ..no additional reserve gas regardless of tank size.

Yes and no, 1/3 of course is still 1/3, but 1/3 of a big tank will get me further than 1/3 of a small tank, at least time wise, and definitely going with the flow.
Let me see if I can make sense of that, just about any size tanks will get me to the EOL of JB on a scooter with thirds, but if something happens and I have to swim out, I'd rather have 2/3's of big tanks to get out than 2/3's of small tanks.

[aquadog196]

Yes, of course...and the 104's if dived to their 1/3rd will most likely get you farther into the cave than the 85's but they will have no more reserve gas to exit than the 85's dived to their 1/3rd.

[PfcAJ]

The argument presented is that smaller tanks get you farther into the cave than bigger tanks. If this is the case, then no, you don't have the same reserve. You have less with smaller tanks.

1/3 of 104s is always bigger than 1/3 of 85s. You still have more time (gas) to fix things with bigger tanks if things go tits up. Math.

[DA Aquamaster]

This isn't a difficult concept to get.

It's about distance and time, and the argument is that smaller tanks allow greater efficiency (in either greater speed or better SAC, or both). But if the emergency is such that you can't maintain that same speed or efficiency during the exit (and most of us would agree this could be the case) , I'd rather have a "third" of 104s to cover a slightly shorter distance than have a "third" of 85s to cover a slightly longer distance.

[Sludge]

This isn't a difficult concept to get.

Apparently, it is.