Doing 'Light Deco' as a recreational diver

[lamont]

There's a difference between "riding your computer up" and having a minute or two of mandatory decompression.

Riding your computer up means diving to 100 fsw, bumping up against the NDLs, then ascending to say 70 fsw and staying there long enough to max out your NDLs again, then going up to 50 fsw and maxing out your NDL. That puts you in a gas loading situation which is not terribly well understood/modelled and it would be good to do longer stops at 20 fsw and 10 fsw when coming up from that.

Simply diving to 100 fsw, going a few minutes into mandatory deco and then ascending to decompress at <= 30 fsw is not 'riding' the computer up.

The big issues with "Lite" decompression is if you are prepared to deal with the worst case at depth. That means that right when you're about to turn when you've already got a deco obligation your buddy has a free-flowing regulator. How fast can you gain control of the situation and start ascending? Do you have enough gas to both deal with the issue at depth and get both of you through the ascent and the mandatory stops? Are you trained to deal with problems at depth? What happens if he kicks your mask off during the air share? etc...

Now with only a few minutes of mandatory decompression on a computer like a Suunto you're probably going to be fine even if you blow it off entirely (but 1 @ 30,20,10 would be a really good idea at a minimum to offgas fast compartments and avoid type 2 DCS). But if you don't have any training you're probably putting yourself at some risk.

How much training is enough? Dunno... I was doing dives like that back when I had 100 dives (75 dives post-DIRF) and on single-130s (but at dive sites that I knew well). After going through RecTriox I learned I was probably a little bit overconfident. YMMV.

One thing that I liked to do back when I dove a computer was to leave the computer in 21% mode while diving EAN32 and then just deco the computer out. That puts you into simulated deco (assuming you know enough to stay out of going into actual deco on EAN32 without needing the computer to tell you), but you have the flexiblity to blow it all off (except the 3 minute stops) if anything truly hairy happens (or you just get too damn cold).

 

[Daryl Morse]

I dive with an Apeks Quantum, versions of which are sold by Dive Rite, Tusa, etc. This computer is quite conservative as compared with Oceanic and other similar computers. Some my buddies dive with Suunto or Mares computers which are also quite conservative. When I do a deep (100+ fsw) and/or long dive on air, my computer has called for DECO (up to 5 - 6 minutes or so) on quite a number of occasions. Normally the DECO obligation clears by the time I get above 40 fsw, occasionally it doesn't clear until I get up to 20 fsw. I've only had to hang once or twice and then only for 2 or 3 minutes. Since it's a conservative computer, this doesn't concern me in the least.

In a way, you have answered your own question in the quotation at the bottom of your posts. Different computers call out different NDL and deco obligations. A few weeks ago, I was diving in Cozumel. We did a deep dive (130 fsw) followed by a dive to around 80 fsw. For those of us with conservative computers, DECO was called for on both dives. For the diver with an Oceanic, it only got one step into yellow. The important thing is to know if your computer is conservative or liberal. If I was diving with an Oceanic computer, I would be much more concerned if it was calling for DECO, but then again, how often would that happen since it is so liberal?

As was pointed out by someone else, diving with a single tank inherently limits the amount of DECO obligation you will incur due to the limited amount of air you are carrying, at least if you want to get back in the boat with air left in your tank.

Also, as was pointed out by someone else, you can avoid the computer calling for DECO by diving with nitrox, which I am doing more and more frequently for this very reason as the length of my dives increases.

 

[Hank49]

I found that some of the people on the dive had their computers show a deco obligation.

is this a fairly common practice?

Thanks

Bjorn

First off, I'm not advocating this practice...I realize the dangers, but yes, I believe it is common, but perhaps not in your area. I've dived soley in the tropics and when I was working and living in the Philippines I can testify that it was common among working divers who were having fun on their time off.

 

[jeckyll]

Lamont: I'm trying not to get overconfident. It's of course hard to say. From what I hear from other, much more experienced divers, they seem to consider me rather conservative

Daryl: I dive the Quantum as well (I think we talked about that before). I wasn't so much asking what I should do, I'm comfortable with the diving I do, but more about what is observed elsewhere. I actually dive my Quantum with the conservatism set higher (SF1) and when it enters deco my buddy still shows 10 minutes of NDL on his old Aladin.
In talking with some folks who recently came back from Mexico, they had the same comments as you. It seems to be SOP down there...

 

[lamont]

Lamont: I'm trying not to get overconfident. It's of course hard to say. From what I hear from other, much more experienced divers, they seem to consider me rather conservative

Yeah, all my current mentors have been hammering on my team to get off our butts and take Tech 1 -- having more experienced divers tell you not to slow down but to speed up is a the better side of that equation to be erring on...

I don't know. Realistically on a Suunto with 5 minutes showing (2 mins mandatory + 3 mins safety stop) you're not in much danger at all. You can probably even go across that by another 5 mins at depth and while the Suunto will probably be telling you 10+ mins of deco to do, you'd be fine blowing it off if the absolute worst case happened to you.

The real question is if you're reserving enough rock bottom gas at that point to deal with a normal ascent plus 10 mins of deco for 2 divers, which comes to around an additional 400 psi for HP130s, or about 1400 psi at 100 fsw -- which gives you 2100 psi usable which is still good for a 30 minute dive at 100 fsw. Given that plan, given at least DIRF or Cavern level of skills, comfort doing OOAs and mask-off, etc and particularly if you're getting mentored by local technical divers then "Lite" decompression sounds not so bad.

If you're just blindly going over your decompression limits on your computer, mindlessly following what deco schedule it gives you and doing so on an Al80 with no idea how much gas you need -- well, that's an accident waiting to happen.

 

[Meng_Tze]

Lamont,
You are on a roll here on SB, in two/three days I have seen so many excellent posts come from you. Truly admirable

 

[H2Andy]

Lamont,
You are on a roll here on SB, in two/three days I have seen so many excellent posts come from you. Truly admirable

SOCK PUPPET!!

:14:

 

[Meng_Tze]

SOCK PUPPET!!

:14:

yeah, yeah charlie

 

[lamont]

Lamont,
You are on a roll here on SB, in two/three days I have seen so many excellent posts come from you. Truly admirable

I've been sick for three weeks and I'm not diving, so I'm doing a lot of posting... Enough posts and some of them have got to be decent... =)

 

[rjack321]

I've been sick for three weeks and I'm not diving, so I'm doing a lot of posting... Enough posts and some of them have got to be decent... =)

You're not still sick from MX are you?? Damn that would be some bad shrimp.