A week later, still can't see the problem.

[Ste Wart]

I was on a technical dive charter last week. The previous evening the owner had rung me and asked me what gasses I would like for the dive. He mentioned that others on the boat would be diving a 20/30 with a 50% deco; the dive would be 55m. After some quick calculator bashing I replied that I would like a 20/20, which would give me an END of 40m. Also the water was about 20 degrees C on the bottom, not cold, with great viz and no penetration.

The next day I went into analyse the gases prior to the dive. The 50% I has chosen was spot on. But when I analysed the back gas I found it to be a 20/30. 10% more helium that I asked for. When I mentioned this the reply was 'this is what the team is diving'.

So?

I wasn't in the team. The other 3 divers were running ratio deco, I was running GAP on a 20/85 GF. To me there was no team, for all purposes I was diving solo, with other tech divers in the water. When I ran the gasses against each other (on Decoplanner; GAP was at the dive charter), I found there was only a 1 minute variation in the schedule, and that was on the deco gas not the bottom gas. The guys doing RD also ran a longer deco than me. So in the event that I did need to share deco gas with anyone, I would be doing more deco than I'd originally planned, no harm there. Same for them if for some bizarre reason they needed to take any of my bottom gas, had I had the 20/20 it would have reduced their required deco, again making the actual deco completed more conservative.

So what was the reason for ignoring my gas request?

 

[Red Sea Shadow]

So what was the reason for ignoring my gas request?

Lack of knowledge?

 

[Tortuga68]

Sounds like a question for the owner. Laziness maybe

...if for some bizarre reason they needed to take any of my bottom gas, had I had the 20/20 it would have reduced their required deco, again making the actual deco completed more conservative

How does 20/20 require less deco than 20/30?

 

[Ste Wart]

Sounds like a question for the owner. Laziness maybe




How does 20/20 require less deco than 20/30?

The math? No idea. But here's what I got off Decoplanner.

20/30 + 50% at 21m

55 20
27 1
24 1
21 1
18 1
15 1
12 1
9 3
6 17

20/20 + 50%

55 20
27 1
24 1
21 1
18 1
15 1
12 1
9 2
6 17

Ok, it is only a minute off at 9m. But it's my bank account the extra 10% is coming out off.

 

[Tortuga68]

Oh, you're using Buhlmann. Good luck with that

 

[Ste Wart]

Oh, you're using Buhlmann. Good luck with that

Wellllll...

I do like messing with the Gradient factors to find the balance in my body.

 

[Red Sea Shadow]

I do like messing with the Gradient factors to find the balance in my body.

Just for my info, if you found an alternative to the GFs, another mean of adding conservatism to Buhlmann's model I mean, would you try it?

 

[Diver0001]

So what was the reason for ignoring my gas request?

I probably would have told him I'd be willing to dive it but that I was only paying for the fill that was ordered...

On the surface of it, it looks like a non-issue in terms of the actual dive and if everyone else feels more comfortable knowing that they can share air with you without thinking about what it will do to their deco schedules then ... yeah....

R..

 

[waterpirate]

Oh the woes of the travelling tech diver are worse than the travelling rec diver. The dive ops statement about the "team" of which you were not a part points to the gas provided to you as being the result of blending laziness.

If the other divers were a "real team" they would have chosen death before they went outside of the team for help, is my experiance. Your gas really had no bearing on them, it only impacted you if you found yourself in a charlie foxtrot. That being the case I would accept anything offered to breathe if I needed it short of a tox mix.

When I travel I have found that fill stations do bank what they consider to be standard mixes. Those standard mixes are seldom what I would mix for myself. When in rome I do as the romans to not agitate the fill station operator, the cost of the helium not withstanding. I avoid the situation you describe by trying my best to talk with the dive op's prior to arrival to sort these things out/or have time to find another fill station.

short answer
prolly laziness on the part of fill station operator.
Eric

 

[Colliam7]

I was on a technical dive charter last week. The previous evening the owner had rung me and asked me what gasses I would like for the dive. . . . But when I analysed the back gas I found it to be a 20/30. 10% more helium that I asked for. When I mentioned this the reply was 'this is what the team is diving'.

I am curious why the owner even 'asked'. When he called initially, he could have said that the op preferred to have all divers on the same gasses (and schedules), he could have said he wanted the other divers in the group to know that you had asked for a different mix before agreeing to it, or that he normally considers all tec divers on a charter to be a single team, etc. etc. I don't happen to agree with those views, but I can understand ops that take that position. In other words, he could, and should, have let you know before you showed up to analyze the gas that there might be an issue. As you suggested and most have agreed, the difference in terms of dive parameters (deco schedules, gas compatibility across divers) was trivial. The only thing not trivial was the additional costs to you. Perhaps, some would even say the difference in cost was trivial (at least compared to the overall cost of the charter and the 20% helium to begin with), but that is your call and not someone else's. I REALLY don't like someone else telling me what gasses I am going to dive, without my input, and that issue has little to do with money. Having said that, I don't know the usual and customary procedures with the charter op you were using, the personality of the owner, etc. And, I don't think there would have been anything wrong with him telling you - when he first called - that 'policy' required you do what the rest of the 'team', or simply the majority of divers, was doing, and that would have given you the opportunity to choose to stay or bail in advance.