Geezer Gas

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You are still working with the assumption that you MIGHT be gas limited which should then result in having a gas saturation difference.

No, I'm working on the assumption that I don't HAVE TO dive as close to the NDL on nitrox as I do on air to be happy with my bottom time. Which means that even if I dive nitrox on nitrox tables, or with my PDC set to nitrox I might very well have a gas saturation difference. It's not an either/or thing, you can have your cake and eat it too.

My NDL times are longer on nitrox, and there are many reasons that I might surface before my NDL time. Gas reserves is the most obvious one to me.


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No, I'm working on the assumption that I don't HAVE TO dive as close to the NDL on nitrox as I do on air to be happy with my bottom time. Which means that even if I dive nitrox on nitrox tables, or with my PDC set to nitrox I might very well have a gas saturation difference. It's not an either/or thing, you can have your leftover cake and eat it too.

My NDL times are longer on nitrox, and there are many reasons that I might surface before my NDL time. Gas reserves is the most obvious one to me.


--
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Typos are a feature, not a bug

I fixed it for you. :D

Still sounds like a rather haphazard dive plan. If I see a risk, I am going to take specific steps to mitigate the risk, not hope for some leftover benefit that may or may not be there dive to dive.
 
Still sounds like a rather haphazard dive plan.
Haphazard? I guess there's a first time for everything. My mates usually grumble about me being too anal.

You might benefit from a refresher course in reading comprehension, though. I believe I already mentioned that I monitor both my NDL and my tank pressure. If that's haphazard, I'd really like to know what makes it haphazard.

Sometimes, when my air consumption is on the high side of normal, I hit minimum gas pressure before NDL, so it's my gas reserve that makes me go shallower. Sometimes, when my air consumption is on the low side of normal, I get uncomfortably close to the NDL before I hit min gas pressure, so it's nitrogen saturation that makes me go shallower. The dive is planned on the basis of both NDL and expected gas consumption. If that's haphazard, I'd really like to know what makes it haphazard. In fact, I believe that most rec divers don't care about min gas pressures at various depths, as long as they're back on the boat with 50 bar/725psi (or 500psi, which I understand is the norm on your side of the pond) left in the tank. Which incidentally, is far from enough for a controlled ascent from 20+ meters' depth while donating gas to an OOG buddy, with enough reserves to do a proper safety stop before surfacing.

Now, to reiterate my previous reasoning, in small, bite-sized pieces:

  • If your gas consumption is similar to mine, your gas reserves won't allow you a very much longer bottom time on nitrox than on air.


  • Sometimes, your gas reserves can limit your bottom time, not your NDL. This depends on tank size and personal gas consumption rate.
  • This is a fact no matter whether you plan/follow an air table or a nitrox table (alternatively PDC set to air vs nitrox).
  • This means that if you dive nitrox you surface with a lower saturation no matter whether you folllow an air table or a nitrox table.


  • Sometimes, your gas reserves allow a somewhat longer bottom time than your air NDL.
  • Your gas limited bottom time may still very well be shorter than your nitrox NDL.
  • This means that if you dive nitrox you still surface with a lower saturation even if you follow a nitrox table.


  • It's only if your gas reserves allow bottom times close to the nitrox NDL that your saturation is just as high on nitrox as it would be on air.

Do you get it now? BTW, there may be other reasons for wanting to surface before your (nitrox) NDL is reached, like a full bladder, or freezing fingers. You can still benefit both ways: Longer bottom time and reduced nitrogen saturation.
 
No need to get personal and lob a bunch of veiled insults based on geographic location or that I don't share your view. This is SB, no one agrees with anyone, get over it.

First, monitoring air and NDL is not the same as planning. One is proactive, one is reactive.
Second, good divers use rock bottom or similar. I don't care what bad divers use. Good/Bad divers are not restricted to geographic location.
Third, yes my gas consumption is most likely better than yours. That matter about as much as your penis size. To many other variables to dwell on.

We simply have a different view on dive planning.
- You are touting that using the unplanned but leftover time before NDL is a tangible benefit.
- I am saying if it's not planned and followed all the time, its not really worth anything.

The difference is if one is looking at a microscopic level of one dive or day of diving or a lifetime of diving. I am going for the long haul.
 
monitoring air and NDL is not the same as planning. One is proactive, one is reactive.
Yes, of course. Before the dive, you plan (i.e. are proactive). During the dive you monitor (i.e. are reactive). I don't know about you, but IME the real, experienced gas consumption will usually differ from the consumption estimate used during planning. Sometimes it's a little higher, sometimes it's a little lower. That's why I monitor both bottom time and pressure, because my plan includes two ascent indicators: Time and pressure.

You are touting that using the unplanned but leftover time before NDL is a tangible benefit.
This is where your error lies. I was touting that using the leftover time before NDL is a tangible benefit. I never said anything about unplanned leftover time.

You automatically and erroneously assumed that I don't plan my dives since I was talking about gas reserves vs NDL times. And that assumption gave you a reason to snark abut my dive planning practice.
 
I should have said using leftover time to NDL to to give you an added safety buffer. I was not clear, my bad.

It is incredibly easy to miss understand what someone else is saying on a board. At this point, its not worth any more of either of our effort, we are generating a lot of heat and no light. Have a great weekend and best wishes for safe and fun dives.
 
I should have said using leftover time to NDL to to give you an added safety buffer. I was not clear, my bad.

It is incredibly easy to miss understand what someone else is saying on a board. At this point, its not worth any more of either of our effort, we are generating a lot of heat and no light. Have a great weekend and best wishes for safe and fun dives.

Do you really follow your dive plan that closely? We plan our dives. Approximate max depth, etc. but the dive ends up being what actually happens. If interesting things are found at shallower depths the dive may be extended. If we have to swim against current the dive may be cut short. If we end up staying longer at depth we leave air to do an extended safety stop to get our computers away from the "caution" zone. We don't know when we start what we will see so it is impossible to know exactly what we will do. I can understand "plan the dive, dive the plan" for tec diving but even then things may change. In my recreational world the plan may consist of hitting the end of the jetty if the current isn't carrying us out and if it is carrying us out to stay in shallower. If the octopus is out playing around before the end of the jetty that dive plan will go away. Dive times will vary with what we actually find.
 
Do you really follow your dive plan that closely? We plan our dives. Approximate max depth, etc. but the dive ends up being what actually happens. ...

That’s my plan when diving for fun. Meander around following what is interesting while keeping in mind where the anchor is and end the dive based on gas supply or NDLs — OK, sometimes a little over when carrying hard reserves and conditions are benign.
 
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Do you really follow your dive plan that closely? We plan our dives. Approximate max depth, etc. but the dive ends up being what actually happens. If interesting things are found at shallower depths the dive may be extended. If we have to swim against current the dive may be cut short. If we end up staying longer at depth we leave air to do an extended safety stop to get our computers away from the "caution" zone. We don't know when we start what we will see so it is impossible to know exactly what we will do. I can understand "plan the dive, dive the plan" for tec diving but even then things may change. In my recreational world the plan may consist of hitting the end of the jetty if the current isn't carrying us out and if it is carrying us out to stay in shallower. If the octopus is out playing around before the end of the jetty that dive plan will go away. Dive times will vary with what we actually find.

Which part of the dive plan are you questioning?

In terms of how how close to NDL (or how much deco I will assume) and what my rock bottom is, those are carved in stone.
If I decide I need a buffer in my dive plan, I won't cut into that buffer mid dive just because I stumbled into something cool.

If you are referring to where I am (depth or position) at what time, of course not.
Screwing around at the end of the dive near the anchor / exit is a time honored tradition of extending a safety stop, built into most of my dive plans.
 
Which part of the dive plan are you questioning?

In terms of how how close to NDL (or how much deco I will assume) and what my rock bottom is, those are carved in stone.
If I decide I need a buffer in my dive plan, I won't cut into that buffer mid dive just because I stumbled into something cool.

If you are referring to where I am (depth or position) at what time, of course not.
Screwing around at the end of the dive near the anchor / exit is a time honored tradition of extending a safety stop, built into most of my dive plans.

My dive plan always includes not going into decompression. With my Oceanic pucks that doesn't mean that people around me are not in decompression. My plan includes an extended safety stop if needed to get my computer out of the "caution" zone. If an emergency comes along that makes it so I can't do the safety stop, then I'm going to take a chance on my computer being right about not being in decompression and hit the surface. If my computer fails I'm going to look at my identical backup. If both fail I will abort unless I know the time and depth are within tables.

Rock bottom air? I probably am willing to stretch that further than I should. I'm pretty comfortable heading up from 100' with 600#. I know people do math that says it won't work but I think my wife and I can both swim to the surface on 600# even under stress. I've done it enough times taking 10 minutes or more and still had air left that I think we can do it together if we have to.

Pretty simple dive plan, isn't it. And it leaves a lot of room for what we want to see.
 

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