"Accidental" deco with 1-day group, what to learn?

[scubadada]

Ummm how would doing side by side comparisons between a series of dives in multideco or VPM using nitrox 32 (the actual gas) compared to side-by-side plans using a Suunto diving the same SIs, depths, and BTs diving nitrox 36 be invalid again? If they have comparable deco schedules you have just demonstrated the validity of Fritz's approach to the Suunto "problem"
I'm sure you'll argue that they can't possibly be identical so this is invalid. I'm continually baffled by the deco micrometer you guys bring to the table.



No really its not. Gaming a computer has ben going on for a decade+ in tech diving circles. Using what you know about a computer (since we don't actually know what's going on in a Suunto) you can adjust it using tools other than just the L0-3 settings. @fmerkel and his wife looked at the issue intelligently - it wasn't a random change and they weren't ignoring it. They adjusted the algorithm, just not through a Suunto approved button.

I can't wait until someone reopens the ratio deco repetitive diving can of worms again.

So if the Suunto algorithm is too conservative, why not get a more appropriate one and dive it according to specs.

 

[Diver0001]

Well.... calling it "gaming the computer" or anything else is just giving it a label to make it sound legitimate somehow. In a similar way we called the 120 rule a "rule" as if it were something other than just a big-ol-ordinary coincidence. I get that.

I know that back when RGBM first came out we needed a strategy to try aligning it with Buhlmann for deco diving in order to be able to make stops at nearly the same depth. There were potentially serious complications because we suddenly had ascent strategies that were vastly different that could force a team to split up during a crucial phase of the dive. As you know we had various solutions to that, none of which I would describe as "pretty" no matter what label we gave it.

However; this is not what is happening here. There are not practicalities of the ascent to be dealt with and nothing about these two computers that would force the divers to take a different ascent line during a no-stop dive. What this diver is doing is looking for a "give me more NDL" button on his computer and there isn't one. That's what's going on here.

His solution for the missing button is to use a fudge (or whatever label we want to give it) and aligning it to another algorithm on the assumption that if you align it at one point that it will automatically be aligned at all points. This assumption is something that intuitively does not make sense given that we do not know what either one of those algorithms (Suunto most of all) is really doing under the hood..... We've had this discussion before and Dr. Powell explicitly warned against making this assumption and since he's one of the most knowledgeable people on the planet about deco theory, I would tend to listen to that. Ergo, I believe if Mr. Merkel is making this assumption that it needs to either be backed up with hard data or it needs to be challenged.

R..

 

[doctormike]

Ummm how would doing side by side comparisons between a series of dives in multideco or VPM using nitrox 32 (the actual gas) compared to side-by-side plans using a Suunto diving the same SIs, depths, and BTs diving nitrox 36 be invalid again? If they have comparable deco schedules you have just demonstrated the validity of Fritz's approach to the Suunto "problem"
I'm sure you'll argue that they can't possibly be identical so this is invalid. I'm continually baffled by the deco micrometer you guys bring to the table

Think of it this way.

Four dives on two days, non-square profiles. That is an essentially infinite number of decompression stress patterns. But yes, you could take any one of those patterns (a specific dive profile and SI), and figure out what EAN fudge factor will get you to line up the ascent profiles between your Suunto and your Aeris. But even that would only be valid for that specific set of dives. It's not like you can say "add 4 to the EAN percentage and it will turn your Suunto into an Aeris", and that is exactly what this advice sounds like to a new diver.

And even if you do figure out the perfect fudge factor for your dive plan, the whole POINT of computer diving is that it tracks what the diver is actually doing, since most dives don't follow the plan exactly, and they give you credit for shallower time and penalize you for deeper time.

What you are really saying is that you can cut a dive plan ahead of time, and then just manipulate the Suunto to follow your desired plan. To which I say, just put that profile on a slate and put the Suunto into gauge mode. At least you will be diving the profile that matches your plan.

They adjusted the algorithm, just not through a Suunto approved button.

They didn't adjust the algorithm, they put in data that didn't correspond to their dive. The computer uses depth, time and mix to model decompression stress. How is entering a fudged mix any better than entering a fudged depth by carrying it 10 feet above you on a float, or entering a fudged time by sending it up 10 minutes early on an SMB? The only difference is that it's a lot easier to fudge the mix.

Normalization of deviance.

 

[NYCNaiad]

....
The learning, or take-away as I see it:
1) Don't dive with a group (>3), especially when you are the least experienced diver and will feel peer pressure to 'go along' well past your comfort.

2) If you are forced into this... Make sure you clarify what your profile limits are, or what your "turn criteria" is. So that nobody will be surprised, or disappointed when you 'thumb' the dive.

3) Get nitrox certified asap. I saw your post about avoiding 'task loading', but it sounds like you are already doing the dives. For the average diver, using Nitrox should not add much stress to the dive, and would have kept you out of deco on this dive. For a ~100' dive, EAN 30-32% should get you around 23m..

Totally agree with #3. Nitrox doesn't really task load & can make a huge difference to the dives. #1 & 2 have me a bit concerned.

re: #1: As a diver, I believe you need to be your own advocate. Regardless of whether you are in a group or not, there will likely be some times that you are put in a situation where you have to decide that your safety is more important than someone's feelings or enjoyment. I think the OP needs to learn to better stand up for himself rather than eschewing groups.

re: #2: There is no reason a diver needs to explain why they are thumbing a dive or worry about disappointing/surprising any other diver. You can end a dive at any time for any reason no explanation or prep necessary. It also seems as if you are suggesting that going into deco is something a diver needs to proactively state to a dive shop they don't want to do. If this is what you are suggesting, I don't agree. By definition, a recreational dives does not involve deco and, therefore, a diver never needs to note this...unless the dive shop indicates this is what they plan on doing ahead of time. At that point, it makes sense for a diver to note their feelings.

 

[NYCNaiad]

...
Honestly, pushing NDL past 1 minute remaining exceeds my comfort zone. To credit the DM, he never "left me on my own" -- he was never more than ~4m away (a distance I was comfortable I could cover fast in an out-of-air situation) and I was comfortable with the plan as-briefed. But as-briefed didn't include any mention of accruing 20+ minutes of mandatory deco!
...
I've always been loth to give the "thumbs up" signal (i've only terminated a dive early once in 75 dives), but in this situation it was probably the right thing to do.
...
One of the reasons I call myself a "conservative diver" is that I do play those scenarios out in my head a fair amount; I read Diver Down a few years ago and that's made me much more mindful of "what if" scenarios. That's one of the reasons I feel so uneasy about how this dive went.
...
I think you're right in that I should have been more aggressive in terminating the dive. I'll learn that for next time..

I applaud you for trying to think of how best to manage things like this in the future. I have a conservative computer as well and am a conservative diver. I don't want to go into deco either and agree with you that you should have thumbed the dive.

I am a little worried about your "I've always been loathe to end the dive" and waxing poetic on only terminating a dive once before. Ending a dive early is not something to be embarrassed about & never ending dives early shouldn't be thought of as positive. I'll repeat what I said a little earlier in the thread...a diver can end a dive at any time for any reason with no explanation. I say this because I'm in your same situation...I am often in a group with an insta-buddy or just the DM. Your safety is of paramount importance & only you can take responsibility for it.

Side note: You said you came up having to pee. You gotta learn to pee in the wetsuit! Gross yes, but way better than needing to pee all the time.

 

[fmerkel]

So if the Suunto algorithm is too conservative, why not get a more appropriate one and dive it according to specs.

Honest simple answer - because the damn thing cost $900. In retrospect probably should have gotten a Peridex but we didn't even know they existed at the time.

Just because we've made some "adjustments" does not mean a we assume everything is now OK. We compare profiles on each dive. We've been diving together a long time. Which ever buddy needs to turn the dive can, which kind of means the most conservative computer. Right now they're kind of equivalent.
I'm not entirely sure what it means yet. Be assured this discussion is putting me on full alert and on a steep learning curve.

 

[gfaith]

Side note: You said you came up having to pee. You gotta learn to pee in the wetsuit! Gross yes, but way better than needing to pee all the time.

You Go girl...

 

[NYCNaiad]

Honest simple answer - because the damn thing cost $900. In retrospect probably should have gotten a Peridex but we didn't even know they existed at the time.

Just because we've made some "adjustments" does not mean a we assume everything is now OK. We compare profiles on each dive. We've been diving together a long time. Which ever buddy needs to turn the dive can, which kind of means the most conservative computer. Right now they're kind of equivalent.
I'm not entirely sure what it means yet. Be assured this discussion is putting me on full alert and on a steep learning curve.

You could still sell it for a portion of the price & buy a different computer on sale/used.

 

[Caveeagle]

re: #1: As a diver, I believe you need to be your own advocate. Regardless of whether you are in a group or not, there will likely be some times that you are put in a situation where you have to decide that your safety is more important than someone's feelings or enjoyment. I think the OP needs to learn to better stand up for himself rather than eschewing groups.

True enough, but I think my point is still valid. When diving as a buddy pair, its pretty simple. Pay attention to your buddy, communicate, dive your plan, and each diver has 100% authority to call the dive. It is much harder to keep communication straight between a team of 3 (or more). And like it or not, there is often some sort of peer pressure NOT to call a dive when you know the group wants to keep going. You have much more control, and its much easier to communicate expectations before the dive begins. And if you have a reason to believe, you will be the first to turn the dive, you should make that clear, maybe even adjust the team/groups based on that.

re: #2: There is no reason a diver needs to explain why they are thumbing a dive or worry about disappointing/surprising any other diver. You can end a dive at any time for any reason no explanation or prep necessary. It also seems as if you are suggesting that going into deco is something a diver needs to proactively state to a dive shop they don't want to do. If this is what you are suggesting, I don't agree. By definition, a recreational dives does not involve deco and, therefore, a diver never needs to note this...unless the dive shop indicates this is what they plan on doing ahead of time. At that point, it makes sense for a diver to note their feelings.

Of course this is true, But if you don't at least recognize that some peer pressure can exist, you are in denial. (probably made even worse when part of a larger 'team', and subordinate to a DM) ..and I stated earlier, that the OP should have called the dive. My point (#2) was that the situation might have been avoidable during the dive planning process.

 

[fmerkel]

You could still sell it for a portion of the price & buy a different computer on sale/used.

True, but so far I wonder why. This is working.
I've heard the warnings. Some of those warnings are being handed down by people that certainly have a LOT more experience and knowledge than me. OTOH, the way I'm looking at it a lot of computers are black boxes, some of them have 'adjustments', and it's not at all clear WHAT THOSE ADJUSTMENTS ARE, or what tweaks have been made to the base algorithm.
When I change my Aladin I have no actual clue what I've done but it's now more conservative simply going from L0 > L1. I can't imagine diving it at L5, it would be teeth chipping conservative. OW1 students might be going in to deco.

We've made an adjustment. It's also becoming evident that we don't know what those adjustments will do across the entire course of a dive and even more on multi-day, multi-dive vacations. But we do know exactly WHAT we did. For now we dive it and watch. We aren't really going to know until that multi-day, multi-dive vacation.

Note - there is always a backup computer on board seeing how that's prudent and the damn thing has a frustrating tendency to refuse to cooperate once in awhile, usually the transmitter, but occasionally the main computer. Don't ever give up your analogue SPG!