Bottom Timer/Wrist Computer Question

[limeyx]

For something that far off the map I'd use Vplanner. Rainer and I are planning a 2 hour dive at 80, and even for that RD is punishingly long.

I'll ask Nick how they run long cave dives.

All of my longer dives so far have been in Mx where we definitely use average depth for 99% of caves, and if there is a steep incline (say like at the Blue abyss where you go 25 down to 100 and up to 25, we just do a slow ascent or min deco up)

I see this in terms of breaking the dive into segments where I am happy to average depths.

I would kind of see this as I will average segments of a dive in the

60-100 feet
100-150
150-200

if a cave goes from 200 to 60 almost vertically, then doing a simple average is not really going to work out that well as you have do do at least *some* deco on the way up.

I dont see how decoplanner or v-planner helps too much here. I guess if you know the exact cave profile in advance and dont deviate then you could use it, but you need a good map or a lot of dives to get the depths.

In a cave obviously you also may do different deco than OW to some extent as you may have a long shallow swim after a deep portion of the dive, so you could conceivably do say less deco on a 50% nitrox bottle but more backgas deco on the exit due to the shape of the cave, and then more O2 deco.

I think to an extent it's all experience, talking to other similarly trained people who use similar gases/approaches etc.

 

[LiteHedded]

All of my longer dives so far have been in Mx where we definitely use average depth for 99% of caves, and if there is a steep incline (say like at the Blue abyss where you go 25 down to 100 and up to 25, we just do a slow ascent or min deco up)

I see this in terms of breaking the dive into segments where I am happy to average depths.

I would kind of see this as I will average segments of a dive in the

60-100 feet
100-150
150-200

if a cave goes from 200 to 60 almost vertically, then doing a simple average is not really going to work out that well as you have do do at least *some* deco on the way up.

I dont see how decoplanner or v-planner helps too much here. I guess if you know the exact cave profile in advance and dont deviate then you could use it, but you need a good map or a lot of dives to get the depths.

In a cave obviously you also may do different deco than OW to some extent as you may have a long shallow swim after a deep portion of the dive, so you could conceivably do say less deco on a 50% nitrox bottle but more backgas deco on the exit due to the shape of the cave, and then more O2 deco.

I think to an extent it's all experience, talking to other similarly trained people who use similar gases/approaches etc.

i just ask others who've done the dive before. i'll compare that with the maps etc. and plan for a range of bottom times

 

[limeyx]

i just ask others who've done the dive before. i'll compare that with the maps etc. and plan for a range of bottom times

Yes, like I said, if there are others who dive similarly to you in terms of gases, profiles and convervatism in diving then thats a great way to do it.

Of course someone(s) had to be the canary

And if everyone did that, then some of the bigger dives would be just impossible or impractical as if you look at standard deco profiles, it's obvious they are far too long for certain dives.

You also still need to take into account your personal willingness in what profile you will run when the cave drastically changes depth in a short distance. Tables aren't always going to give you a reasonable answer here...

 

[LiteHedded]

Yes, like I said, if there are others who dive similarly to you in terms of gases, profiles and convervatism in diving then thats a great way to do it.

Of course someone(s) had to be the canary

And if everyone did that, then some of the bigger dives would be just impossible or impractical as if you look at standard deco profiles, it's obvious they are far too long for certain dives.

You also still need to take into account your personal willingness in what profile you will run when the cave drastically changes depth in a short distance. Tables aren't always going to give you a reasonable answer here...

yea exactly. these are all just tools. if all else fails I just get out of the water.

 

[Scott L]

Min deco (RD for recreational profiles) wasn't covered in your GUE-F class? That's rather shocking.

You weren't taught how to use average depth in place of max depth with NDL/MDL tables (and how to adjust this average based on the actual profile)?

If you're not using a computer and you're not using average depth, what are you using? Max depth only? I'd pass...

Yes, as it related to rec diving and the 120 rule. I do not remember the concept being labeled as such though. I am a DIR neophyte... It will not take much to trip me up at this juncture in time...

 

[ucfdiver]

yea exactly. these are all just tools. if all else fails I just get out of the water.

Give it your best estimate and let DAN pay for it if you're off, right?

...that's what I do. So far I'm a good ways over 100 deco dives and DAN's gotten off pretty easy

 

[Rainer]

That's how it was covered in my class, too. 120-rule (with 20% depth credit for 32%) or 130-rule (32%, no depth credit; this is slightly more conservative) on top of average depth. Discussion covered how to average depth (5 min segments, comparison between gas used over time given known SCR, what to do when going shallow->deep vs deep->shallow, etc). The same principles basically apply to deeper dives where you come up with an average and then can apply either RD or pre-cut tables. In all cases, though, depth average plays a role. As noted by many, this isn't necessarily the same average that a gauge might be trying to give you, so as always, don't turn off your brain.

Yes, as it related to rec diving and the 120 rule. I do not remember the concept being labeled as such though. I am DIR neophyte... It will not take much to trip me up at this juncture in time...

 

[LiteHedded]

Give it your best estimate and let DAN pay for it if you're off, right?

...that's what I do. So far I'm a good ways over 100 deco dives and DAN's gotten off pretty easy

that's where the fitness part of it comes in

 

[limeyx]

Give it your best estimate and let DAN pay for it if you're off, right?

...that's what I do. So far I'm a good ways over 100 deco dives and DAN's gotten off pretty easy

Are you here for a reasonable discussion or just looking to create an argument?

 

[ucfdiver]

Are you here for a reasonable discussion or just looking to create an argument?

Sorry Nick, just joking with Brian. We're friends in "real life" and dive together semi-often, so please understand that wasn't trying to piss him off. I figured this discussion has basically drawn to a conclusion. If there's still open discussion about what anyone's doing, I'd be glad to participate, but frankly litehedded and I do things darn near identical, and it sounds like you're applying some of the same concepts to ratio deco as we're applying to the use of tables.

All of these algorithms and methods are reasonably well tested. I'm a fairly firm believer that hydration, rest and fitness make substantially more difference than slight variations in deco schedules. Once we narrowed it down to what everyone was doing, I just can't see discussing it much further without getting the image of "measuring with a nanometer and cutting with an axe" in my head.

I know a decent amount of people who have been bent-- at least 10-15, and nearly every one of them was either:

• Overweight
• Dehydrated during the dive
• Not well rested.

Of course, these 3 seem to come together a lot around NFL, as many people are drinking heavily on Friday night and doing a 2 hour dive on Saturday morning.