Multi Gas Computers...worth it?

[texdiveguy]

In addition to my statement above,,,,I have yet to see a He computer and companion software for OC trimix diving I feel totally good about. It is a fact that most DCS incidends involving OC trimix dives involves divers using He computers as primary. The safest and best method is sticking to the basics---timers/gage mode computers and cut tables.

Now for NDL recreational diving profiles on air or nitrox a computer is a great thing. **The VEO 180 is a good basic computer for the money.

 

[loosebits]

To all the people who just say "cut tables", what do you do in a deep cave? For example, say I'm diving in Peacock 3 (around 50 - 60') and I jump off to Henley's Castle (around 180') and hang out there for about 5 mins.. that would be fairly difficult to plan on tables without knowing exactly how long it's going to take me to make the jump.

Now, after I dive it a few times and I get a feeling for how long it takes me to reach that jump I can cut some decent tables but the first couple of times I may be doing a 90 min dive with 5 min at 180' and the bulk of it at 60'. That's a lot of uneeded deco.

I understand WKPP people just use ratio deco but I'd trust a Nitek He or VR3 more than that.

 

[grazie42]

I´m not full cave but I am taking that course in the fall. (Which basically means I know nothing of cave deco and since I´m only cavern, not much about cavediving either)

BUT in the process of evaluating instructors for my course I asked this same question.
The answer I got (from all of them) was to play around with deco software and look for patterns. If you use the same gasses (BG and deco) you´ll find that 1 minute @ depthrange a-b will equal x minutes of deco, @ depthrange c-d 2x minutes etc...

WKPP people aren´t the only people using some form of "ratio deco"...

P.S What kind of gas are you breathing that lets you go from 60 to 180ft on a whim, and how often do you do it 11

 

[PerroneFord]

I understand WKPP people just use ratio deco but I'd trust a Nitek He or VR3 more than that.

I wouldn't. But that's just me.

But to your example, if I plan my dive at 60ft, then I will do a 60ft dive. I'm not just going to "take a detour" from 60ft to 180ft on a whim. First, my backgas would kill me. Second, I'd be configured differently. Third, I wouldn't bounce dive to 180ft for 5 minutes.

But I am not a technical diver, so maybe others might feel this is legit. I'd think if I were going to do a jump from 60-180, I'd wanted to have planned for that in advance, taken the proper mix, and the proper gear.

 

[texdiveguy]

Just getting back to this post..... Mr. L., I would like to hear more detail to your 180' bounce dive within that cave system......your 'planned' profile/back and deco mixes/team member (re)actions,,etc......or maybe you were just thinking aloud,,,,say in the context of an extended range air dive like was common place in years past.

 

[loosebits]

I wouldn't. But that's just me.

But to your example, if I plan my dive at 60ft, then I will do a 60ft dive. I'm not just going to "take a detour" from 60ft to 180ft on a whim. First, my backgas would kill me. Second, I'd be configured differently. Third, I wouldn't bounce dive to 180ft for 5 minutes.

But I am not a technical diver, so maybe others might feel this is legit. I'd think if I were going to do a jump from 60-180, I'd wanted to have planned for that in advance, taken the proper mix, and the proper gear.

This isn't "on a whim". Lets say I'm planning to make that jump which is some distance back in the cave which most of it will be at 60'. I can't plan it as a multi-level dive because I don't know how long it will be before I reach that jump.

P.S What kind of gas are you breathing that lets you go from 60 to 180ft on a whim, and how often do you do it (

)

I've never done this dive, I've only got 15 cave dives or so since I got my full cave card. My understanding is most people do the bulk of the dive on 32 (in stages) and then 18/35 for their backgas.

Just getting back to this post..... Mr. L., I would like to hear more detail to your 180' bounce dive within that cave system......your 'planned' profile/back and deco mixes/team member (re)actions,,etc......or maybe you were just thinking aloud,,,,say in the context of an extended range air dive like was common place in years past.

I was just looking for an example where you have a multi-level dive (where the bulk of the time is spent shallow) but you don't have enough information before your first dive there of how long it takes to get to your maximum depth. This generally wouldn't happen on wrecks, you plan to be at 180 for 20 min and then 90' for 20 mins, you have the ability to execute that exact plan. In caves, the cave and your swimming speed determines the profile.

 

[PerroneFord]

I was just looking for an example where you have a multi-level dive (where the bulk of the time is spent shallow) but you don't have enough information before your first dive there of how long it takes to get to your maximum depth. This generally wouldn't happen on wrecks, you plan to be at 180 for 20 min and then 90' for 20 mins, you have the ability to execute that exact plan. In caves, the cave and your swimming speed determines the profile.

Ok, Hypothetical.

Lets say your team and my team are going to make this dive. You guys are faster swimmers than we are. Both of us take 18/35 on backgas, and 32 on stages. We both plan a 2 hour run time. For the sake of argument, none of us bring oxygen or a rich deco mix.

Your team gets to the jump at 35 minutes, my team gets to the jump at 45 minutes. We both spend 10 minutes exploring at 180ft, come up, and exit following our plan. We both exit the cave at exactly 2hrs.

Here is the magic question. Does it make any difference at all in the gas plan, that we hit that jump 10 minutes later than you? I'd be curious what decoplanner, vplanner, GAP, or Nautilus have to say.

 

[loosebits]

Probably not... but let's make it a 3 level dive... 60' for some distance, 150' for some distance and then a pre-determined duration at 180' before turning.

It just seems that there is a real benefit of using tables for gas planning (over-estimate all of your times) but then use the computer for the execution so you don't have all the excess deco. On a wreck, I don't really see a lot of benefit to computers but it seems to make sense in a cave if you don't trust ratio deco.

 

[PerroneFord]

but it seems to make sense in a cave if you don't trust ratio deco.

On this, we agree. However, I'll probably still dive my table, and use the computer information if need be for an aborted dive, or something else that falls outside the scope of my cut tables. Meaning we are exiting earlier than planned. Buying a computer expressely for this purpose locks me into a VR3 or something similar if I start to do trimix dives. For nitrox dives, this wouldn't be necessary.

But Ratio Deco or equivalent is just as viable in my opinion.

 

[Jay Roy]

Probably not... but let's make it a 3 level dive... 60' for some distance, 150' for some distance and then a pre-determined duration at 180' before turning.

It just seems that there is a real benefit of using tables for gas planning (over-estimate all of your times) but then use the computer for the execution so you don't have all the excess deco. On a wreck, I don't really see a lot of benefit to computers but it seems to make sense in a cave if you don't trust ratio deco.

Just out of curiosity, why dont you trust ratio deco?