how to dive with non-DIR divers?

[rjack321]

Now, if I'm diving with an experienced DIR diver that proposes RB numbers lower than mine, I'll be a lot less likely to assert that my figures are the correct ones.

DIR divers should never ask you to do a "trust me dive". Work through the numbers together and chose the more conservative plan.

It should take <5 mins. A unified gas plan is part of the system.

 

[PerroneFord]

Now, if I'm diving with an experienced DIR diver that proposes RB numbers lower than mine, I'll be a lot less likely to assert that my figures are the correct ones.

If s/he is truly DIR, then that diver will dive the more conservative numbers.

 

[Phil K.]

Now, if I'm diving with an experienced DIR diver that proposes RB numbers lower than mine, I'll be a lot less likely to assert that my figures are the correct ones.

LG - The essence of DIR is team diving, which underpins the use of standard gear and standard gas mixes. RB pressure, or BTW what GUE now calls "Minimum Gas," is gas reserved for the other members of the team in the event one of them has an OOG emergency. It's their gas. The so-called "experienced DIR diver" in the scenario you described who insists on using his lower Minimum Gas number (presumably in order to extend the BT of the dive) is foolishly allowing his gas in your tanks to drop below the amount needed so that you can both safely ascend to the surface if he has an OOG emergency. Minimum Gas is non-negotiable. It is what it is for each diver and to protect the interests of each team member, the diver with the highest Minimum Gas must be used as the team's Minimum Gas and the basis for determining the team's Turn Pressure. You should never give into peer pressure to fudge your Minimum Gas. I'd rather be safe than have a couple of minutes added to the BT. This is a "rock bottom" safety issue. If you did that on a dive with me, I'd never have you on my team again.

Next time you confront a diver not inclined to limit the dive based on Minimum Gas, ask him at what minimum pressure should the team begin its ascent so that on the surface the divers have 500psi or whatever sort of PADI, recreational rule he's using.

 

[LG Diver]

LG - The essence of DIR is team diving, which underpins the use of standard gear and standard gas mixes. RB pressure, or BTW what GUE now calls "Minimum Gas," is gas reserved for the other members of the team in the event one of them has an OOG emergency. It's their gas. The so-called "experienced DIR diver" in the scenario you described who insists on using his lower Minimum Gas number (presumably in order to extend the BT of the dive) is foolishly allowing his gas in your tanks to drop below the amount needed so that you can both safely ascend to the surface if he has an OOG emergency. Minimum Gas is non-negotiable. It is what it is for each diver and to protect the interests of each team member, the diver with the highest Minimum Gas must be used as the team's Minimum Gas and the basis for determining the team's Turn Pressure. You should never give into peer pressure to fudge your Minimum Gas. I'd rather be safe than have a couple of minutes added to the BT. This is a "rock bottom" safety issue. If you did that on a dive with me, I'd never have you on my team again.

Next time you confront a diver not inclined to limit the dive based on Minimum Gas, ask him at what minimum pressure should the team begin its ascent so that on the surface the divers have 500psi or whatever sort of PADI, recreational rule he's using.

Phil, I think I may have misrepresented what I meant to say, and the specific situation that it was applicable to (lack of coffee will do that). The extent of my diving with DIR divers thus far is a couple of dives this past weekend where I was in a single LP95 and the two other divers were in double X7-100's. Point being that they were not reliant on the gas in my tank for their backup as a) they had tons more gas than me, and b) they had each other as backups. Likewise, I had no concerns that they would not have enough gas to support me in an OOG, as my single tank and my horrible SAC rate would be the limiter on both dives. We discussed RB in the pre-dive review and we all acknowledged that I would be the limiter. In this case we set my RB at 500 PSI with a max anticipated depth of 40', so with 2500 PSI in my tank at the start, diving halves, the turn pressure was agreed at 1500 PSI. There was no confrontation, argument, or peer pressure in this instance.

My prior comment was more hypothetical. My point being that I'm now armed with a little bit of information (how to calculate RB) but my assumptions may not be real-world. For example, my calculations of RB might include 2 min at depth to sort the problem out, and then two divers ascending at 60'/min at a stressed SAC rate of 1 cfm each, with a 3' safety stop at 15', and a 200 psi pad on top of that. Being relatively new, I have basis to know whether this is a ridiculous amount of padding, so if my calculation puts RB at 1000 PSI but a more experienced diver suggests an RB of, say 800 PSI I might be inclined to listen to them judgement of what an acceptable amount of padding is. I may be totally off on this, but this was the reasoning behind my previous comment- not that anyone pressured me into diving with a lower RB than I was comfortable with. In any case, thanks for the comments.

-John

 

[rjack321]

John if you and I were diving together...

1) we would go through RB calculations together since your new at these and a bit of scubamath practice never hurt anyone.

2) we would pad the RB calculation, the max depth and whatever else to suit the most conservative diver. Whether that conservatism was due to tank size, or experience level, comfort, or some other factor wouldn't matter.

In your example case, you really weren't part of the team planning yet. But if I'm in doubles and you're in a single I still plan on you being part of my reserves. Having another 3rd teammate along doesn't mean you or your resources are unimportant - the reserves should get bigger not just the liabilities.

BTW, Its not just gas, but lights, SMBs, masks, spools, etc.

 

[Phil K.]

John,

I think it's great that you are being inquisitive about these issues. Most of us gravitated from recreational diving and had to learn a lot of new things and re-learn some others to make the transition. When you take DIR-F, this will become clearer to you. No matter how much formal training you get, one of the essential ways of progressing is to dive with better trained and more experienced DIR divers than yourself as often as you can. The DIR divers I know want to expand the circle of divers they are comfortable diving with and understand that we all need mentoring to get better at it. This forum is really a reflection of that. However, one thing, we can't do here is substitute for a solid foundation beginning with a fundies class. More likely we'll end up confusing you and that's not good. Even if you don't feel ready for fundies, your willingness to seek out DIR divers and ask questions and soak up what you can shows that you're headed in the right direction. My guess is, just like the rest of us, one question leads to another leads to many many more and you quickly realize the need to start formal training.

Phil

 

[Ben_ca]

John and I did dive together and here's how the gas planning went....
3 divers
1 X single 95 @ 2400
1 double 100 @ 3500
1 double 85 @ 2500

training site...
can surface anywhere (1/2's)
max depth is around 45 FSW

limiting factor is single 95... rb calculations were:

1 min = emer
3 min = stops
X 2
8 Cu Ft @ tank factor of 3.5
228 psi

default to min Rock bottoms... of 500 psi

We were a bit fast in the calculations... This was John's first dive with DIR trained (fundies) divers so we did the pre dive SADDDD (haven't gone over the GUE EDGE yet) and didn't want to "instruct" him on anything... just dive and observe.

As far as his involvement in the briefing and planning it was fast and probably some of it went over his head..... but then again we all have the standard training places where we already have run the math a dozen times (our bunny slopes) so the SADDD goes a bit faster.

Fire away

:flame:

 

[Phil K.]

Well, for starters you didn't specify John's SAC rate, but more importantly you didn't multiply the result by the average ATAs before dividing it by the GUE tank factor and multiplying by 100. Assuming SAC = 1.0 and avg ATAs = 1.675 (based on max depth = 45 fsw) you'd get Minimum Gas of 383 psi. True enough, you'd still round this up to 500 psi, but your computation was seriously flawed and, but for the shallow maximum depth, could have resulted in a significant understatement of John's Minimum Gas.

 

[rjack321]

That's how I would have done it (except for maybe slowing down a bit... )

My comments were addressing the thinking that: those two doubles divers are each others redundancy, I'm just along for the ride. :no

No free DIR rides

 

[Ben_ca]

Well, for starters you didn't specify John's SAC rate, but more importantly you didn't multiply the result by the average ATAs before dividing it by the GUE tank factor and multiplying by 100. Assuming SAC = 1.0 and avg ATAs = 1.675 (based on max depth = 45 fsw) you'd get Minimum Gas of 383 psi. True enough, you'd still round this up to 500 psi, but your computation was seriously flawed and, but for the shallow maximum depth, could have resulted in a significant understatement of John's Minimum Gas.

I used 1 for his SAC...
and 1 for ATA's

The max depth is 45... most of the dive was planned for the training area around 30 FSW...

So going back to the OP's questions of how you dive with non-DIR divers... how would you have done it?