Gas management skills...

[MikeFerrara]

NetDoc once bubbled...
covers SAC and gas/dive management in detail. Although, I only present the concept of SAC in BOW and how Boyle's law creates a different DAC as well.

Lets face it, there is a lot to learn about diving. Not sure I could convince many to take a two year course to get it all in :tease:

But Mike, there are lots of people who invent these tools to help them cope, only to find that there are lots better tools out there.

The addition of basic gas management only adds a little extra time to the class at a level that'll work for a new diver at shallow depths. I also try to give them enough so they understand the magnitude of deciding to do vacation trust-me dives and the kind of gas planning that needs to be done for deeper dives. Like they say "you don't know what you don't know".

The other night I was talking with the father of a 16 year old student of mine. He was telling me about some of his dives. I turned the discussion to the planning of those dives. After all, my student is going to be diving with this guy. LOL Anyway we got around to gas planning and when to start the ascent. Well, long story short I got a blank stare.

It's amazing how many never consider the possible need to have enough gas to get two people to the surface or how much that might take. I guess there is always the rapid ascent as a backup plan right?

 

[MikeFerrara]

Big-t-2538 once bubbled...


Certainly you do not want to take credit for Split Fins do you?

No. LOL but I may have been one of the first to realize that they don't work cuz they're broken up the middle. It wasn't til much later that I understoof the brilliance in it though. I mean really...knowing how so many divers are tought to kick and the frequency of cramps. All that was missing was a fin that didn't meet resistance in the water. Not a chance that many would notice the loss of control since they never had any in the first place.

 

[Walter]

"All that was missing was a fin that didn't meet resistance in the water. Not a chance that many would notice the loss of control since they never had any in the first place."

I love it!

 

[detroit diver]

I've never seen a dive op look at my SPG when getting back on the boat. I usually ignore the "500 psi" garbage because I use a rock bottom number, which is always higher.

Before learning rock bottom, I used to surface with about 50 psi. Not too bright, but, hey, what did I know?!!

NetDoc once bubbled...
I have seen the 500-700 psi given by charters and some instructors misinterpreted to the extreme. Incredibly, divers have blown off safety stops and shortened deco stops to MAKE SURE they got on the boat with the prescribed minimum. Sorta makes my jaw drop.

 

[fins wake]

I have seen the 500-700 psi given by charters and some instructors misinterpreted to the extreme. Incredibly, divers have blown off safety stops and shortened deco stops to MAKE SURE they got on the boat with the prescribed minimum. Sorta makes my jaw drop.

Good point! This is scary stuff, and I guess we've all seen it. I think Bret Gilliam once wrote something along the lines of 'what are you going to do with that extra air at the surface, trade it in?' This is really something which OW instructors should impress in students from the start, never cut safety stops for the sake of having the minimum ...

The addition of basic gas management only adds a little extra time to the class at a level that'll work for a new diver at shallow depths. I also try to give them enough so they understand the magnitude of deciding to do vacation trust-me dives and the kind of gas planning that needs to be done for deeper dives.

Good stuff. Wish there were more instructors like you and Pete out there ...

 

[The Chairman]

I cover the concept during Boyle's law... how/where do you do it? I am always willing to add more info.

 

[ElectricZombie]

Rule of 1/3 or Rock Bottom Calculation

 

[MikeFerrara]

NetDoc once bubbled...
I cover the concept during Boyle's law... how/where do you do it? I am always willing to add more info.

I the context of a PADI course layout...

In an effort to tie related things together, while discussing boyale's law (though the OW text doesn't name the law just explains how it works), I reference the effects on gas consumption. I bring it up again in module 2 where the buddy system is covered. I talk about it in module three which deals in part with emergency management and I make a big deal about it in module 4 which covers dive tables and planning.

 

[GreenDiverDown]

...that I don't remember being taught much about gas management thru PADI all the way up to and including OWSI.

I now use rock bottom. But unlike others who seem to "get on the boat" with their TOTAL RB, I begin the ascent before reaching RB and "get on the boat" with only my BUDDY'S PORTION of the calculated RB...not BOTH my gas AND his gas. And sometimes I might stay at my safety stop and burn his gas as well since at that point in the dive he no longer needs it to surface. So there are times when I surface with less than the typical "500" .

I also use my rock bottom figure and calculate out and back...half out and half back after subtracting RB. This works for almost all of my diving.

Also, my RB figures might be a little skinny compared to others. I use a .6 working and .4 at rest for my gas and 1.0 working and 1.0 at rest for my buddy. Ascent time is rounded up to the next whole minute. Ascent ATA is the avg. depth of the ascent. I use a 15 ft safety stop when teaching but deep stops if just diving. The gas calculations come out the same BTW...because of the way that I round up. If I want to be more conservative I can quickly just double my buddy's gas or 1.0 for both divers working and at rest.

SA

 

[Charlie99]

Stephen Ash once bubbled...
[BAlso, my RB figures might be a little skinny compared to others. I use a .6 working and .4 at rest for my gas and 1.0 working and 1.0 at rest for my buddy. Ascent time is rounded up to the next whole minute. Ascent ATA is the avg. depth of the ascent. I use a 15 ft safety stop when teaching but deep stops if just diving. The gas calculations come out the same BTW...because of the way that I round up. If I want to be more conservative I can quickly just double my buddy's gas or 1.0 for both divers working and at rest.[/B]

I have done similar calculations, but some different assumptions (3cfm total for me and excited buddy, 1 minute delay before ascent, 50fpm. Alternative requirement is just me, and multiple deep stops, slow ascent). After doing all of the math, for the depth range of 70' to 110', the old 100psi / 10' of depth is pretty darn close when using an AL80.