I have a dumb question about cave training

[ScubaSquatch]

I was looking at TDI's course outlines and it says "Rule of 1/3's for single tank and 1/6th for doubles" I understand the rule of 1/3's but why after cavern and during intro do they cut that back to a 1/6th when you're on SM or BM doubles? You have twice the amount of gas but they limit you to effectively the same amount as if you were on a single tank. It did say after full cave you're allowed 1/3's. Is it to keep the dives shorter?

 

[Chris H]

Yes.

 

[fish149]

To limit the linear distance into the cave.

 

[PfcAJ]

Much of the learning at the intro level is gathered in the first part of the cave. Running line, a lot of the dramatic depth changes are in the beginning, keeping the team together, sorting out pace, etc.

1/6 gas rule keeps you close to the door with a relatively large amount of reserve gas and lets you do two dives comfortably on a set of doubles.

1/3 of a single is dumb. Don't do that.

 

[KevinNM]

Thirds is the minimum, not what you 'should' be doing. There is no margin for errors on thirds. Like the error in this report:
Two German divers drown at Gran Cenote Kalimba at Tulum

 

[The Chairman]

For one thing, it will encourage you to get additional training so you can dive thirds. My cynical mind tells me that's all there is to it.

 

[rjack321]

I was looking at TDI's course outlines and it says "Rule of 1/3's for single tank and 1/6th for doubles" I understand the rule of 1/3's but why after cavern and during intro do they cut that back to a 1/6th when you're on SM or BM doubles? You have twice the amount of gas but they limit you to effectively the same amount as if you were on a single tank. It did say after full cave you're allowed 1/3's. Is it to keep the dives shorter?

They (nonsensically) allow you to dive a single tank for cavern & intro.
Because they made a mistake allowing that in the first place, they have to make a second mistake and to allow you enough gas to actually do something besides duck your head under and turn around. So they allow 1/3rds on a single.
Agencies can be dumb sometimes.

Smart agencies start you off in cavern and intro in doubles and diving 1/6ths. That gives you tons of reserve which you will probably end up dipping into when you have to do OOA gas sharing exits or light-less blinds exits.

 

[Lorenzoid]

Smart agencies start you off in cavern and intro in doubles and diving 1/6ths. That gives you tons of reserve which you will probably end up dipping into when you have to do OOA gas sharing exits or light-less blinds exits.

I think I recall reading that NSS-CDS ditched the Cavern course entirely, requires Apprentice (the new first-level course) to be done in doubles, and because there is so much variation in tank sizes, they set a particular volume of gas as maximum for penetration--50 cf?

But yeah, to answer the OP directly, it's to keep us (I myself being at just such an intro level) on a short leash. It occurs to me that if I have to solve a problem, it may take me a lot longer than someone with more experience. Knowing I can afford to be methodical while I solve it because I have all the gas in the world should help keep me calm.

 

[rjack321]

I think I recall reading that NSS-CDS ditched the Cavern course entirely, requires Apprentice (the new first-level course) to be done in doubles, and because there is so much variation in tank sizes, they set a particular volume of gas as maximum for penetration--50 cf?

Its more like GUE's and NAUIs three step GUE-F/ITT then Cave1/Cave2 progression now.
Cave Diver - NSS-CDS Training Program
CDS Basics / Apprentice / Cave

Since cavern and intro are often combined (when offered in 2 parts) anyway.

 

[Manatee Diver]

I think I recall reading that NSS-CDS ditched the Cavern course entirely, requires Apprentice (the new first-level course) to be done in doubles, and because there is so much variation in tank sizes, they set a particular volume of gas as maximum for penetration--50 cf?

Cavern is still in the NSS-CDS Curriculum but is a pure recreational class only done in singles and doesn't count toward cave training at all.