Might be a stupid question but.....

[rick00001967]

Sorry, there was more hiding between my sentence...I was more referring to a cavern certified diver diving thirds... and wanting to drop a bottle in a cavern for their cavern dive if a) team separation, b) double gas failure c) some other scenario.
_R

i def see you concern. i can assure you, i do not actively dive caverns and NEVER have gone beyond that zone. if i am lucky, i get to dive a couple of cenotes maybe once a year.

although the "rule of thirds" was discussed during training, it was also discussed that using this as a gas planning rule is not usually recommended as a more conservative approach is usually needed in this type of diving.

for the rest....my question was a hypothetical one. it was based on a "cave" dive scenario, not a cavern dive, and yes, it was assuming the worst possible circumstances while planning "as if" a diver was solo. perhaps i am assuming incorrectly that most cavers plan as if they were alone ?

 

[rick00001967]

It’s very unlikely that more than one person would need it. 1 extra tank is better than none and you can’t have too much gas. I personally would not have a problem with each member dropping a safety bottle but that could make a mess of the line on a busy day.

this was my thinking as well. and the small inconvenience of dropping a tank seems to be more than offset by the possible up side. but i guess that is a feeling not held by all.

now your last comment about making a "mess of the line" would not be something i would have thought of. hence my original question. i would imagine that depending where you dive, some sites may get quite busy at times. so there may be a valid argument that it is just not practical and may in fact do more harm than good. thx !!

 

[OTF]

Not a cavern diver, but wreck diver. We occasionally leave an 80 of air or nitrox at the bottom of the line on wreck dives. This is NOT a stage that's part of the normal dive plan (we always carry those), but a backup for use in the event of an emergency.

 

[rick00001967]

More reserve on your back eliminates all that. You can share it. You can isolate it. You can monitor it. Its *with you* at all times.
Keep it simple.

so the lesson being, if you really believe you may need the extra gas, it may be better to just carry it with you.

i guess in my newbie mind, i was maybe comparing my hypothetical scenario to what i have read and seen done on wreck penetration dives and deep dives. perhaps this was a mistake. but i know many wreck divers will leave stages at the entry point of a wreck for example. (someone mentioned this earlier) or a deep diver may leave a spare bottle on a decent line "just in case".

i guess it comes down to the details of that particular dive. you may feel the need to have extra gas, but perhaps carrying it through a certain section of the cave for instance, may not be possible or practical. in these cases it "may" be better to leave it, rather than keep it with you. but barring this, your advise would be to keep it simple and keep it with you. thx !!

 

[rick00001967]

Not a cavern diver, but wreck diver. We occasionally leave an 80 of air or nitrox at the bottom of the line on wreck dives. This is NOT a stage that's part of the normal dive plan (we always carry those), but a backup for use in the event of an emergency.

and this was my way of thinking as well. sorry, my terminology may not have been accurate. my use of the term "stage bottle" was meant for any bottle left somewhere along the way. but i understand your distinction.

 

[macado]

It depends. As others stated for teams of 2, thirds is not really conservative. This is over-simplifying it but thirds essentially allows two divers to share the gas burden in the event the third teammate has a catastrophic gas loss. Most people recognize that diving to 1/3s is not really conservative in a two person team but I suspect most people do it anyway all the time.

Having more gas in the cave is never a bad thing but sometimes it's a balance between efficiency and "do you really need to carry that extra bottle?" Carrying an extra bottle does add drag especially in a high flow cave. You need to stop to drop it, clip it to line, turn it off check/pressure. I realize that only takes a minute or so but when you combine that with the extra drag you may have found you could have gotten further without carrying the extra bottle.

I do sometimes leave bottles in the cave for extended periods of time. Most of the time these are simply "safeties" for rebreather dives. This is very situational and may not be the scoop of your question.

A couple easily examples would be Eagle's Nest or Ginnie Springs. If I'm going to be diving over multiple days in a row I'll do a setup dive and leave bottles in the cave for the next few days. It's really convenient to have bottles already deployed. You will want to check them and verify they're still full otherwise they're not really safeties at that point.

If I am solo I often leave "safeties" in the cave that I don't factor into my gas planning. This applies to scootering as well. If I plan for a scooter failure I may need a lot more gas to get out than I did to get in.

TL;DR - solo / scootering / rebreather dives are typical scenarios when I will take "extra" bottles with me. A normal OC dive with in a team of 3? I don't usually bother for that but if we're planning something complicated or new to me then maybe.

 

[p_kos]

It depends. As others stated for teams of 2, thirds is not really conservative. This is over-simplifying it but thirds essentially allows two divers to share the gas burden in the event the third teammate has a catastrophic gas loss. Most people recognize that diving to 1/3s is not really conservative in a two person team but I suspect most people do it anyway all the time.

Having more gas in the cave is never a bad thing but sometimes it's a balance between efficiency and "do you really need to carry that extra bottle?" Carrying an extra bottle does add drag especially in a high flow cave. You need to stop to drop it, clip it to line, turn it off check/pressure. I realize that only takes a minute or so but when you combine that with the extra drag you may have found you could have gotten further without carrying the extra bottle.

I do sometimes leave bottles in the cave for extended periods of time. Most of the time these are simply "safeties" for rebreather dives. This is very situational and may not be the scoop of your question.

A couple easily examples would be Eagle's Nest or Ginnie Springs. If I'm going to be diving over multiple days in a row I'll do a setup dive and leave bottles in the cave for the next few days. It's really convenient to have bottles already deployed. You will want to check them and verify they're still full otherwise they're not really safeties at that point.

If I am solo I often leave "safeties" in the cave that I don't factor into my gas planning. This applies to scootering as well. If I plan for a scooter failure I may need a lot more gas to get out than I did to get in.

TL;DR - solo / scootering / rebreather dives are typical scenarios when I will take "extra" bottles with me. A normal OC dive with in a team of 3? I don't usually bother for that but if we're planning something complicated or new to me then maybe.

Yah, takes about 5-10 seconds to drop/pick up the safety bottle once you get the hang of it, the team doesn’t even have to stop swimming most of the time. Leaving the bottle on the line when doing multiple dives is fine, same with primary reel (although leaving a primary for multiple days is generally frowned upon).

 

[halocline]

hey all. i am only cavern certified. this question is for information only. i do not dive caves.....EVER.

...if i am using doubles with 3000psi each, i must turn the dive with at least 2000psi in each (in reality the dive should be turned before that)..... so why not leave a stage at a point in the cave when you reach 2500psi in each tank (half way in) ?

i understand many might say this is unnecessary as you would have at least one buddy with extra gas. but from the standpoint of planning AS IF you were solo and being self reliant, is this something anyone would do ?


thx
rick

I have a couple of comments to offer:

1. If you are planning as if you were solo, you would not dive to thirds. Solo cave diving is a different world with lots of extra training and there is a plausible argument that it's never safe. So I would just leave out the 'planning as if you were solo' part altogether. Cave diving is taught as a team sport, and teammates rely on each other for all sorts of things. Dive with reliable team mates. That's ultra important.

2. If you are concerned that you don't have enough gas to exit in a worst-case scenario (that is within the realm of reality, not just imaginary) then you have to turn sooner, it really is that simple. What you are talking about is a de-facto use of a stage to extend a dive past the point where you would feel comfortable with just your back gas. That technique typically has it's own training and that usually comes well after full cave. There are added complexities of stage diving and you'll likely appreciate that when/if you take a stage class with a good instructor.

Thirds is aggressive with a two person team, more and more cave divers are not comfortable with thirds, although IMO the flow, navigation, and any other dive specifics will determine appropriate penetration limits.

I wouldn't feel badly at all about posing this question even as a cavern diver, because it's always interesting to discuss stuff like this. I would just keep in mind that generally speaking, deeper penetration dives are riskier (or at least more complex) and require more experience and training. Not just more gas, which kind of what you are suggesting.

 

[lostsheep]

Since the next course in the Cave curriculum is diving 1/6ths or 1/3 of 2/3rds while going past the cavern zone... and then you progress to thirds...

1/3 of 2/3?...2/9ths?

 

[flymolo]

I was taught to drop one Al80 of EAN32 (typical back gas in Florida) per team about 400’ into a cave when diving in a team of 3 within NDL limits and using the rule of 3rds as part of NAUI Cave 1. Just as a backup if things really go pear-shaped and given that statistically most drown within about 400’ or less of a cave’s exit point. Overkill? Perhaps, but not much of an inconvenience so worth it in my opinion. Gets you practice dropping/picking up stages if nothing else, good perpetration for Cave 2 where stage dropping becomes a necessity.

I'm not a huge fan of this strategy. If I'm bringing an extra AL80, I'm breathing it on the way in, and preserving my backgas.