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[tomfcrist]

130ft isn't something that I know of anyone that would use 21/35 on that, but that depth is part of why 25/25 and 30/30 exist. That said on those dives for that depth you should be using 50% instead of O2

I get that. However while referring to AJs post, I deliberately used the most reasonable of the WKPPs standard gasses.

 

[PfcAJ]

I get that. However while referring to AJs post, I deliberately used the most reasonable of the WKPPs standard gasses.

No one on the Wkpp would do the dive you described. Nor would they use those gases.

 

[stuartv]

@stuartv why ppO2 of 1.4?
remember that IMO the biggest benefit of standard gases is mixing convenience *provided you don't do ratio deco, where the ease of that is definitely the biggest advantage* so while you may end up with 28% for your ideal fO2, if you blended it the way we blend standard gases you'd end up 28/13. That would be perfectly fine to choose for that depth if you want 1.4, though I don't.

Two big arguments against standard gases are the fact that they target a bottom ppO2 of 1.2 instead of 1.4, and they put a lot of helium in compared to others by keeping the ppN2 around 2.7.

The question was to figure out what you thought was the "best" ppO2 and ppN2 to target to see what real benefit you thought you were getting.

Why 1.4? Because it gives me a longer bottom time and less deco than 1.2.

I take my cylinders to get them filled. I tell them what mix I want. I come back, analyze them, and take them away. It costs me the same and takes the same effort from me whether I get 28/20 or 21/35 or 18/45 (apart from the difference in cost of the helium itself).

So, 1.2 is DISadvantageous. Ease of blending is irrelevant (to me). I don't do Ratio Deco, so no advantage for me there.

Having a gas that gives me a longer NDL or less deco is advantageous to me.

And, finally, if I'm doing something where a Standard Gas DOES give me some advantage (e.g. blending, or it's available in banked form or whatever), my Best Mix training totally permits me to use that gas and have that advantage. If I were limited to only using Standard Gases, then there would be many times I would have gases that are less optimal than with Best Mix - for no advantage.

This debate seems to be sort of like people only learning to drive an automatic transmission and insisting that that is better because it's easier. Yes, Best Mix means I do one simple calculation to determine the optimal gas for my planned max depth. SG is easier because you just look up the gas on a chart. After that, it's the same (presuming you're planning using a computer). Learn the one extra calculation and you can drive either kind of car and choose which is right based on what you're doing. You can still drive an automatic, if you want to. Learn only the automatic and you are limited, in comparison.

TBH, @tbone1004, I feel like you aren't a true Standard Gas person. You are simply an "easy blending" person. That means you happen to usually use Standard Gases, but it's a function of logistics/convenience, not that limiting yourself to Standard Gases has an advantage, per se. I have no problem at ALL with using a gas that is a few points off from "optimal" for the sake of convenience. Or even for the sake of money. I have dived Air a number of times when Best Mix would have been 24 or 25%, simply because it's cheap and easy to get an Air fill. And then dived on Air to 150 or 160! OMG! Because my training allows me to do that without throwing off my method for calculating deco.

I only have a problem with the statement that Standard Gases is "more flexible" or that Standard Gases somehow allow a diver to get in more dives than they might if they use Best Mix. That is just bunk.

 

[PfcAJ]

It’s not unheard of. But I agree it’s unusual. I wanted to streamline the pattern for you...fewer variables as you would say.



I agree that it’s unlikely. But if we are going to use an extreme example of unlikely dives and their outcomes...I’ll refer to Simons reasoning for the rediculousness of the NEDU profiles...”it’s all for science”. If we are going to highlight the disparity between gas efficiencies, we need to make it stupid enough to note the difference.

The only reason I added deco gasses at all was because it’s completely unrealistic to do a dive like that without having some kind of bailout deco gas.



Yeah I get that...so add a helium percentage to the back side...it doesn’t change the deco obligation.



You aren’t good at math evidently...

A 2 person team slinging 2 85’s each can make that dive. 1 with O2, 3 pumped up with bottom gas.

So the only way you can make a point is to create a totally made up dive profile? This isn’t an NEDU study, dude. Come on man. Get it together.

Team bailout is such a ridiculous protocol that (again) you have to cook up an unrealistic and unsafe profile for it to even seem reasonable.

You’re an instructor? Bless your heart.

 

[tomfcrist]

No one on the Wkpp would do the dive you described. Nor would they use those gases.

What gas would they dive at 130’?

 

[stuartv]

Can someone clue me on on why 75 minutes of BT at 130', on a CCR, in the ocean, is so unbelievable? (I really wanted to say unfathomable, but I couldn't keep a straight face while I typed it )

I realize it's a far cry, but I did 47 at 135' last summer, on OC, using only 1 deco gas, on the wreck of the Tarpon, off NC. It seemed like a long-ish hang, but not remotely "undoable".

I'm not (yet) a CCR diver, but 75 at 130 on a CCR doesn't seem like it would be that much of a stretch. I mean, with all I read about people doing 6, 8 or 10 hour cave dives on a CCR, which is a 3 hour dive on an ocean wreck so preposterous?

I'm not to be snarky or argumentative. I am calling out my own ignorance and trying to learn something.

Is it because it would be unwise to commit to being in the water that long when ocean conditions can change so rapidly? Is it because of the bailout gas requirements?

Don't the guys doing wreck dives in the 300 - 400' range have in-water times that are as long? One friend of mine is doing those kind of dives. I'll have to ask him what he thinks....

 

[tomfcrist]

So the only way you can make a point is to create a totally made up dive profile? This isn’t an NEDU study, dude. Come on man. Get it together.

Team bailout is such a ridiculous protocol that (again) you have to cook up an unrealistic and unsafe profile for it to even seem reasonable.

You’re an instructor? Bless your heart.

LMAO. I’ll go do a 75 minute BT ocean dive at 130’ tomorrow if you’d like...it’s not totally made up. It’s completely doable.

Team bailout isn’t nessecary until you go batshit with the profile...at a certain point it becomes nessecary...unless you are in a cave.

 

[PfcAJ]

What gas would they dive at 130’?

50% as first deco gas, oxygen as last gas, and 18/45 on the bottom.

21/35 isn’t a gas we use for anything except 190 deco gas, and even then the helium content is often higher.

 

[tbone1004]

@tomfcrist how does slinging lp85's with only one of the of O2 count as compliant with NAUI's tech program?
You can't do that dive with 85's though, you need 340cf of gas for your 1.5x diver rule and cave filled lp121's are pushing it. No way you could do it with 85's.

also, no one slings 85's of O2, nor would anyone of sound mind use O2 on that dive to 130ft. EAN50 is a much more logical gas for that, especially if there's any helium. For the run times you described you'd need two bottles anyway so you split it up with 50% and 100%, or since it's the ocean and you're in the mid-atlantic, probably 80%

@stuartv on a CCR it isn't unreasonable, but on a CCR you'd carry a lot more helium in the mix because you didn't plan on using it outside of bailout. 21/35 is what would be in all of my buddies dilout tanks for a 130ft ccr dive, ESPECIALLY if it was for over an hour.

What do you see as the downsides of running 1.4? sure it racks up less deco, but it's not without fault, especially as you are getting into trimix depths....

 

[PfcAJ]

2hrs plus in the ocean (especially when you could break that up into shorter dives) isn’t responsible. Conditions change too fast.