Rock Bottom

[Coldwater_Canuck]

What's a rock bottom time?

Rock bottom pressure I meant ... what this topic is about.

 

[AndyNZ]

It was an SI shop where I learned the skill. PADI and NAUI did not cover what you do with a SAC rate after you figure it out.

Not strictly speaking true.

There are plenty of PADI standards in various courses (OW, AOW and Deep) that actually say (paraphrased) "determine how long a tank of air lasts at depth".

I can't speak for NAUI, but there is nothing in the PADI system that precludes teaching gas management at OW level or any other course. Personally, I deal with it conceptually at OW (explain the concept of minimum gas reserve and apply thirds/halves of usable gas) and then do the math in either AOW, Nitrox or Deep.

 

[Adobo]

Not strictly speaking true.

There are plenty of PADI standards in various courses (OW, AOW and Deep) that actually say (paraphrased) "determine how long a tank of air lasts at depth".

I can't speak for NAUI, but there is nothing in the PADI system that precludes teaching gas management at OW level or any other course. Personally, I deal with it conceptually at OW (explain the concept of minimum gas reserve and apply thirds/halves of usable gas) and then do the math in either AOW, Nitrox or Deep.

Not to try to learn to dive in the internet but, when would you recommend to your students to use thirds of usable gas when diving recreational profiles?

 

[scubadada]

I'm sorry, I just can't do this rock bottom stuff. I'd lilke to get in my own enjoyable dive. I'm not coming up from 100 ft with 1300 psi in my 80 cu ft Al tank. Chastise me all you want, I'm showing up back on the boat with +/- 500 psi. If you don't like it, I'm not your buddy, I'm certainly not going to ascend with you (but would be more than happy to watch you start up while I finish my dive, I've done that for a number of reasons, usually gas consumption)

Good diving, Craig

Bring on the insults, shields are up, full power

 

[MXGratefulDiver]

I'm not going to 100 feet on an AL80 ... I'd rather spend a nice, relaxing 65 or 70 minutes at shallower depths on a tank that small.

... Bob (Grateful Diver)

 

[Gombessa]

I'm not coming up from 100 ft with 1300 psi in my 80 cu ft Al tank. Chastise me all you want, I'm showing up back on the boat with +/- 500 psi.

The takeaway isn't that you should do a dive to 100ft and come up with 1600psi in your AL80 (and just to note, you COULD do a dive to 100ft and still "be back on the boat with 500psi" while adhering to rock bottom pressure).

Rather, you just won't see too many divers who adhere to rock bottom doing 100ft dives in an AL80--they'd choose an appropriate tank(s) for the dive.

 

[HenrikBP]

I'm sorry, I just can't do this rock bottom stuff. I'd lilke to get in my own enjoyable dive. I'm not coming up from 100 ft with 1300 psi in my 80 cu ft Al tank.

It is my understanding that Rock Bottom Pressure is *not* a static pressure carved in stone prior to the dive. If you ascend from that 100 ft at your pre-determined rock bottom pressure - for that depth - to say 50 ft, then a new rock bottom pressure is now in effect.

A more complete understanding of Rock Bottom may make it more palatable

Lamont's paper on Rock Bottom is a great read and very well worth the time:

Rock Bottom and Gas Management for Recreational Divers

Henrik

 

[Bismark]

It is my understanding that Rock Bottom Pressure is *not* a static pressure carved in stone prior to the dive. If you ascend from that 100 ft at your pre-determined rock bottom pressure - for that depth - to say 50 ft, then a new rock bottom pressure is now in effect.

A more complete understanding of Rock Bottom may make it more palatable

Lamont's paper on Rock Bottom is a great read and very well worth the time:

Rock Bottom and Gas Management for Recreational Divers

Henrik

Bing! We have a winner

 

[amascuba]

Its been on my mind for a while, but I've finally learned a bit about gas management and exactly what Rock Bottom is and I am wondering why this isnt taught in OW classes ? It seems like such a crucial concept and one that might not really be considered by begining divers unless they were exposed to it.

I also wonder if experienced recreational divers actually adhere to it when making and diving a plan ?

Based upon my observations from reading many posts by instructors; they feel that the generic open water student isn't capable to or doesn't want to learn the math involved to calculate even just generic gas management. (Hence, be back on the boat with 500 psi...) I'm sure that some would feel that formulating a solid dive plan based around rock bottom would be to complicated to teach.

On the other hand, there are instructors who do actively teach gas management, in fact I know of at least two instructors in your area who are capable to teach it effectively.

I'm aware that I may be stirring a hornets nest here, but it is what it is.

 

[MXGratefulDiver]

The problem with "be back on the boat with 500 psi" is that it's not planning ... it's reacting to circumstances.

And unless you can formulate HOW to do it, it's like giving someone driving directions by telling them to turn left two blocks before the red light.

... Bob (Grateful Diver)