BradJ
Guest
How many of you actually practice "rock bottom" when doing an open water, recreational dive?
Rock Bottom
- Thread starter BradJ
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vodolaz
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Why wouldn't I?BradJ:
WJL
Contributor
BradJ:
But DIR is not "everyone else."
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BradJ:
I view 500 PSI as the end goal, and "Rock Bottom" as the methodology that tells you how to achieve it.
... Bob (Grateful Diver)
MHK
Guest
BradJ:
Brad,
The sad part is that, as you say, "everyone else is doing the 500 psi routine" Sadly, everyone is doing something that makes no sense.
For example if you are doing a dive to 130', how much air do you need to have in your tank if an OOA situation happens for you and your buddy to get home, including stops?
If you are doing a 100' dive, how much gas do you need to reserve??
If you are doing a 60' dive how much gas do you need to reserve??
Telling someone to be back on the boat with 500psi leaves the diver lacking critical information, is poor planning and is an incomplete thought. It certainly isn't how I would approach a dive..
Ask yourself what is the more important question, how much to have in your tank when you arrive on a boat -v- how much to reserve so if your buddy comes up to you OOA that you'll have enough to get both of you home and not blow off any stops or violate your ascent rate strategy just because one team member ran OOA??
Once you answer that question, you should conclude that doing the "500 psi routine", isn't the safest way to approach a dive.
Hope that helps.
Later
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Perhaps this isn't the place to get into gas management vis-a-vis "DIR vs. everyone else". What I think, however, is that it isn't a mutually exclusive thing. Nor do I think it's accurate to say "everybody else is doing something that makes no sense". Because, frankly, there are other agencies and instructors out there who teach perfectly sensible gas management techniques ... many bearing a striking resemblence to what DIR teaches (physics is pretty agency-independent, after all).
To a degree, I understand where you're coming from. However, what's missing from the standard "500 psi routine" is the methodology for actually figuring out ... based on profile, SAC rates (both divers), and cylinder volume ... how much gas you need to safely surface from a given depth if an OOA occurs. That's the value of "rock bottom".
The "500 psi thing" is a rule of thumb ... a simplistic way of saying, "don't surface with an empty cylinder". What makes no sense is giving someone a rule of thumb without giving them the tools for figuring out how to achieve it. That's not gas management at all ... it's a guessing game.
Where our opinions differ is in the concept that "everyone else" does this. I understand the concepts of gas management fairly well ... including how to calculate rock bottom. I didn't learn it in a GUE class. So obviously, there are other people out there who are teaching these things.
... Bob (Grateful Diver)
To a degree, I understand where you're coming from. However, what's missing from the standard "500 psi routine" is the methodology for actually figuring out ... based on profile, SAC rates (both divers), and cylinder volume ... how much gas you need to safely surface from a given depth if an OOA occurs. That's the value of "rock bottom".
The "500 psi thing" is a rule of thumb ... a simplistic way of saying, "don't surface with an empty cylinder". What makes no sense is giving someone a rule of thumb without giving them the tools for figuring out how to achieve it. That's not gas management at all ... it's a guessing game.
Where our opinions differ is in the concept that "everyone else" does this. I understand the concepts of gas management fairly well ... including how to calculate rock bottom. I didn't learn it in a GUE class. So obviously, there are other people out there who are teaching these things.
... Bob (Grateful Diver)
MHK
Guest
NWGratefulDiver:
Bob,
Didn't mean to suggest that anyone couldn't learn this, what I was offering was my response to Brad who stated that everyone does the 500psi thing. I'm not trying to split hairs or play games of semantics, but my comments were in response to the stated fact by someone else that "everyone else is doing teh 500psi thing"
In my view, the 500psi thing, that I agree is commonplace doesn't go far enough because it gives the end result, but doesn't give the student any meaningful information. What a student [ or diver for that matter] needs to know is how much gas do I need to get from the bottom, allowing time to square away the accident, allowing time for 30fpm ascent rates and allowing for appropriate stops..
Hope that clears up my comments and sorry if they were taken another way.
Regards
VTernovski
Contributor
BradJ:
I found this to be an invaluable tool, and I am shocked it never occurred to anyone (including myself) to teach me this simple concept before taking the DIR-FUN class. Now, mixing this and other concepts of calculating NDL, and remaining gas based on your depth and tanks (all without a computer), and then realizing that your depth gauge now becomes your backup bottom timer just completely blows my mind and leaves me in a perpetual state of euphoria... so, to answer your question, hell yeah, of course I am using it!
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