RMV math…

[tursiops]

Are you really defending this practice???
Are you actually saying you never ever gas planned even one dive like this (because you don't know your RMV) and are just stair-stepping from prior successes? That is pretty close to the definition of Normalization of Deviance, IMO.
I'm really glad this thread was moved to Advanced. New divers shouldn't see this nonsense (not that they can't anyway).

LOL! Can you imagine his gas-blending procedures? Or regulator tuning? "There, that seems about right." Let's hope he always uses the same size tank....

 

[scubadada]

I would never take @60plus diving recommendations as safe. Know your gas consumption and plan your dives,

 

[Kendall Raine]

Now that the thread has been moved to Advanced,

Which, in the big picture, is kind of a shame since the concepts of gas management and dive planning (SAC; instead of "return with 500 psi" or "I know how long a 12 L tank will last" or whatever other gibberish) really are basic concepts, which, in the interest in pushing bodies/dollars through intro classes, often get left until much later.

Anyway, good for you for trying. Valiant effort. Not wasted, except perhaps on 60plus.

 

[rsingler]

Which, in the big picture, is kind of a shame since the concepts of gas management and dive planning (SAC; instead of "return with 500 psi" or "I know how long a 12 L tank will last" or whatever other gibberish) really are basic concepts, which, in the interest in pushing bodies/dollars through intro classes, often get left until much later.

Anyway, good for you for trying. Valiant effort. Not wasted, except perhaps on 60plus.

Then in the Basic Forum, make a comment in
Thread Why Surface with 500 PSI?
which will bring it back to the top of the Basic Forum for further discussion. I'm really not just promoting my old thread, but responding to your comment about the nonsense of "return with 500 psi", which is a subject I feel strongly about...

 

[tursiops]

Which, in the big picture, is kind of a shame since the concepts of gas management and dive planning (SAC; instead of "return with 500 psi" or "I know how long a 12 L tank will last" or whatever other gibberish) really are basic concepts, which, in the interest in pushing bodies/dollars through intro classes, often get left until much later.

Anyway, good for you for trying. Valiant effort. Not wasted, except perhaps on 60plus.

Thanks. I think I'll try and write a post for Basic that gives a progression from "trust your dive guide" to "come back with 500 psi" to ..... The key will be to encourage moving from the starting blocks without terrifying someone afraid of math or numbers. The key always is to give someone something to do....rather than telling them what not to do....

Then in the Basic Forum, make a comment in
Thread Why Surface with 500 PSI?
which will bring it back to the top of the Basic Forum for further discussion. I'm really not just promoting my old thread, but responding to your comment about the nonsense of "return with 500 psi", which is a subject I feel strongly about...

I'll have to reread that thread and see if it has gone in a useful direction or is it now just omnidirectional noise...

 

[rsingler]

I'll have to reread that thread and see if it has gone in a useful direction or is it now just omnidirectional noise...

What? A ScubaBoard thread that has gone Off Topic!?!
Yeah, time for a new one, @tursiops . Go for it!

 

[Kendall Raine]

Thanks. I think I'll try and write a post for Basic that gives a progression from "trust your dive guide" to "come back with 500 psi" to ..... The key will be to encourage moving from the starting blocks without terrifying someone afraid of math or numbers. The key always is to give someone something to do....rather than telling them what not to do...

A post on planning and gas management in Basic would be great.

 

[60plus]

The obsession with SAC / RMV must be an American thing. It is not in the PADI manual and I have never heard it mentioned at numerous dive centres. Neither do I hear it mentioned on recreational club dives. We discuss intended dive time and depth and note pressure at buddy check but never calculate gas usage. The emphasis is on regularly checking your SPG and NDL time. Some of these divers I dive with are very experienced OC and CCR divers who are certified any gas / any depth and when deep diving they do do calculations on how much bailout gas they might need, but if something goes wrong at 100m plus late in the dive they only carry enough bail out gas between 4 of them for 1 diver, so they are depending on no more than 1 CCR failing.
Diving to 40m within NDL limits is regarded as "No stop" diving, ie you can if necessary ascend straight to the surface without decompression or safety stops at a rate of 1 ft per second. From 40m that is only 2 minutes 11 seconds for which very little gas is needed. If you are into a bit of deco and you have an OOA your are going to grab your buddy, get on their octopus and get up to 15 or 10m sharpish.

Is NASA just stair stepping from from prior success? Why not just calculate it and go for the Moon or Mars first flight?
Why return to the surface with 500 PSI ? (generally 50 bar on this side of the Atlantic) The answer is "to surface with any more is a waste of valuable dive time"

 

[scubadada]

Do what you like, Blind Faith (fitting), 1969

 

[60plus]

Was Eric Clapton a Scuba diver? did he calculate gas consumption?

PS my elder sister was an avid vinyl collector in the 60s

As is now probably clear I cannot understand this obsession with SAC. To go back to the gasoline car analogy. If on a full tank I can get from A to B and have 1/2 a tank left, then surely I should be able to get from A to C on a full tank if A to C is only 1 & 1/4 the distance between A and B. I do not need to know the mpg. What is useful to know is the factors that could vary that mpg, not its absolute value.