Going into deco

[TSandM]

Okay . . . It's confession time. This came up over the weekend, where my husband did a repetitive dive and racked up what his Mosquito told him was 22 minutes of deco (which is kind of absurd on a dive with a max depth of 90 feet, but where the vast majority of the dive was spent around 50 to 60, but that's what the instrument said). Since it wouldn't give him any credit for time served below 20 feet, he ended up with about a ten minute hang at 10 feet, which he did. Gas was no issue.

Yeah, I know, I know, you shouldn't do decompression diving unless you're deco certified and are diving doubles and have appropriate decompression gases and do your gas management ahead of time. But I suspect that Peter's not the only one who's ever done this. In fact, I know Catherine does deco from time to time.

My question is: Who has deliberately gone into deco on a recreational dive, and how did you figure out how much deco to do? Did you do what your computer asked for? Did it make any sense?

 

[SparticleBrane]

Never once.

 

[Gil57usa]

Normally I dive doubles and do the proper gas management plan to extend bottom time past NDL's. On a couple occasions I did slide a bit past the NDL's. Fortunately my computer is a cochran EMC-16. Not only did it tell me I was in Deco, it told me what depths to stop at and did the appropriate countdown for each stop. No problems.

 

[MXGratefulDiver]

Lynne, I'll betchya that Peter did a reverse profile (going deeper on the second dive than on the first) ... Suunto computers penalize you heavily for doing that.

I go into deco regularly (according to my Vytec) ... all I do is come up very slowly from 60 feet ... spending progressively longer intervals at the 40, 30, 20, and 10 foot levels. The computer is usually satisfied long before I am ...

... Bob (Grateful Diver)

 

[nereas]

I have not deliberately gone into deco on a non-deco dive.

Sometimes there are features in the software of the dive computers that trigger an extended stop for various reasons, such as because of a rapid ascent, or a spike dive profile, or something similar. It is not always a case of merely having extended your bottom time too long.

I believe it is a good idea to follow the computer in waiting out these extended stops, as long as you have enough nitrox or air left in your tank(s). The computer is supposed to help you dive a safe dive. If you don't follow it, then what good is the algorithm in it for you?

 

[SparticleBrane]

I think I see where this is going.

 

[DandyDon]

I take it that Mosquitoes are the more conservative ones that penalize the diver so they can advertise they're safer...?

 

[Sharky1948]

a reverse profile (going deeper on the second dive than on the first)(Grateful Diver)

Well, usually I'm in violent agreement with Grateful Diver. However, in this case I'd like to point out that a "reverse profile" generally refers to a single dive in which the latter part is deeper than the first. That is linked to higher probabilities of DCI.

In the case of a second dive being deeper than the first, recent evidence is that it has no impact on DCI incidents.


With respect to the OP, prior to deco training and doubles I did trust my computer for limited deco diving. The only time it "surprised" me was when I over compensated and came up too slowly, creating additional deco obligation.

 

[do it easy]

While we are all confessing...

This happened to me once when I was practicing with multiple stages and lost track of which bottle I was breathing. :11: I thought I was breathing the stage, but I was actually breathing my backgas. I spent most of the dive at 50', but I did spend around 20-30 minutes at 80' (off the top of my head, the details are a bit fuzzy). Anyhow, on the way out of the deep section, I realized I had racked up some deco time from the 80' excursion AND that I had lost track of my gasses. I think I had about a 12 minute hang at 20', but I knew I was cutting it close on the amount of air (maybe that explains the fuzziness?) As my regs got harder and harder to breathe, I would switch to one that was easier. I finally finished my time, but it was pretty close. I was able to unscrew my regs without turning the tanks off. :no

The computer I was using was fairly conservative and liked to deco at shallow depths. Given my profile and the fact that I didn't spend all the time at 80', I could have probably shaved some time off if I needed too, but there was no immediate need to shorten my deco time.

 

[nereas]

I think I see where this is going.

Nice twin tanks in your avatar, Sparticle. Are those twin 130s or twin 140s? They look really huge.