Dangerous lies?

[Patoux01]

Interesting but I have never seen a diver doing the "inbetween" alternative

Anyone not going to NDL is doing an "in-between".

If the switch from air to nitrox extends your NDL by 20 minutes (completely virtual case) but you only use 10 more minutes of that NDL before being gas limited, you are technically "safer" from a gas loading point of view than having gone up to NDL be it on air or nitrox. Therefore you're doing "in between".

 

[Freewillow]

I understand PAtoux but I do not believe that this is what was meant by the op.

What I have never seen is , for example, a diver with nitrox 32 dive with his computor meant for nitrox 28.

Plus, I see potential problems with the MOD, doing this. So safe? I am not sure.

 

[kelemvor]

Interesting but I have never seen a diver doing the "inbetween" alternative

I almost always do in between. My dives tend to be gas limited or buddy limited or boat time limited.

 

[Damselfish]

Interesting but I have never seen a diver doing the "inbetween" alternative

I pretty much always do the "inbetween" alternative, as I suspect most people do whether they think of it that way or not. It would take some effort for me to do otherwise.

I understand PAtoux but I do not believe that this is what was meant by the op.

What I have never seen is , for example, a diver with nitrox 32 dive with his computor meant for nitrox 28.

Plus, I see potential problems with the MOD, doing this. So safe? I am not sure.

I do think it is what was meant, but I also don't think it matters. Whether you're setting your computer to a more conservative (for NDLs) percentage and dive closer to what it says, or leave the O2 setting accurate and just not diving to the NDL given, is the same as far as your body is concerned.

I don't think a lot of divers do the 32/28 type of thing you're describing, but I'd bet some do. (f I see that an ops Nitrox tanks are inconsistent, I sometimes set my percentage to the lowest I am seeing and just leave it there, instead of messing with it all the time. So probably more of a 32/30 thing, but I do that too.)

I don't see potential problems with MOD. It's pretty easy to remember what your MOD is. I don't rely on any sort of alarm to tell me about it. You don't mention accumulated O2 time, but you would also have to work kind of hard at that in rec diving to make it the limiting factor.

 

[BRT]

Interesting but I have never seen a diver doing the "inbetween" alternative

We do almost every dive.

 

[MXGratefulDiver]

Interesting but I have never seen a diver doing the "inbetween" alternative

Seriously? Unless you dive to the limit of your NDL, that's exactly what you're doing any time you dive ...

... Bob (Grateful Diver)

 

[boulderjohn]

Interesting but I have never seen a diver doing the "inbetween" alternative

I'll join the chorus--most people diving nitrox do the "inbetween" alternative. Just as one example, if you use the PADI air tables, you have an NDL of 25 minutes at 90 feet. If you are using EANx 36 and do the same dive, you have an NDL of 40 minutes. Most people would not have enough gas to get to 40 minutes on such a dive and would probably quit at maybe 32 minutes.

When I am doing recreational dives in South Florida, a typical first dive is a wreck at a depth of 100-110 feet, followed by a reef dive at about 50 feet. I usually show up for such a dive sequence with a tank of 32% and a tank of 36%. Over the past few months I have charted both dive profiles in posts on this topic, showing that after the two dives I have racked up considerably longer bottom times than I would have on air, and I am considerably farther away from NDLs.

 

[*dave*]

"If you don't have enough weight, just allow some water into your BCD and it will add enough weight to allow you to descend"

That gem came from an IT/IC for SSI

 

[boulderjohn]

"If you don't have enough weight, just allow some water into your BCD and it will add enough weight to allow you to descend"

That gem came from an IT/IC for SSI

Amazing.

I would guess that if the person saying that had not thought about it before and had been given that as a problem on a test of dive physics, he or she would have thought it through and realized it had to be wrong. I think that is an example of something I have long observed--if people get an idea in their heads, they will cling to it even though it is so clearly wrong you would think it would be obvious. I first observed this when bicycle riding with a friend in high school, and we came to a fork in the road that offered two different paths to our destination. The first was over a dam and followed the shoreline of a reservoir--unquestionably completely 100% flat every inch of the way. The second was a winding path that my friend insisted we should take because it was downhill the entire way. I told him it was downhill for a long way, and then it was steeply uphill. He insisted it was not uphill at all--he remembered distinctly that it was a downhill thrill ride the entire way. I asked how it was possible for one route to be perfectly flat and the other completely downhill and still arrive at the same final point. He insisted. We took the different routes, and I had to wait an hour for him to arrive, thoroughly exhausted from his strenuous climb. This friend was in the honors program at school, bound for a major university.

I have since seen this in many, many places. People will firmly believe the most outrageous nonsense, and once they believe it, they will not be dissuaded. Recent research, in fact, indicates that for some people, providing absolutely solid contradictory evidence makes them hold to their beliefs even more strongly than before. Scuba certainly offers many such examples.

 

[KevinNM]

I have since seen this in many, many places. People will firmly believe the most outrageous nonsense, and once they believe it, they will not be dissuaded. Recent research, in fact, indicates that for some people, providing absolutely solid contradictory evidence makes them hold to their beliefs even more strongly than before. Scuba certainly offers many such examples.

So, did your friend ever tell you again how it was all downhill?