extending a recreational dive into short deco?

[kafkaland]

May I assume from this you had not agreed on max. depth and bottom time before the dive started? In case of two different computers there's no way of telling which one will signal first or even if there is a true deco obligation.

And no, I don't trust computers for this kind of decision making I prefer to calculate on forehand and stick to the plan not the computer.

Well, there is something to that. As to maximum depth, we didn't bring a shovel, so that defined it, but we have admittedly been sloppy when it came to planning bottom time. Even with a plan of "use the NDL limit per computer", I recall looking at the plan feature and saying something like "this should give us about x minutes at 120'. Had my buddy done the same, he might have noticed a slightly shorter time due to mix (he was on 28%, I had 29%) and possibly algorithm. This would have tipped us off that he would likely be the first one to signal and I mighty have prompted him when I was getting close my limit. If the deco obligation was mostly due to differences in the dive profile, though, this wouldn't have helped much.

 

[kr2y5]

So doing the extra five minutes is no big deal? Well, at that point my dry suit was leaking and during those long, cold extra five minutes I was cursing my buddy for the deviation from our plan

I hear you, but to be fair, let's look at it from your buddy's perspective: you did not inform him ahead of the time that your drysuit was leaking, and that you were getting so cold that another 5 minutes would have been a big deal. I think it's safe to assume that there's usually a little bit of responsibility for the lack of communication / anticipating problems on each side. IMO, just as it's good to leave a bit of a buffer in terms of gas and NDL/deco, it's also good to have some buffer in terms of thermal comfort, so that you don't have to suffer if you are delayed for some reason.

 

[Jack Hammer]

Not too long ago I was on the other end of a scenario like that, and didn't appreciate it much, to say the least:

New buddy, Great Lakes wreck dive to about 120 ft. He had doubles, I was in sidemount. Neither of us had deco training. The plan was to stay within NDL, but do an extended five minute safety stop because we knew it would be close and the water was cold. The dive itself went smoothly, I had about 2 minutes of NDL time left when we started to ascend. When we reached safety stop depth, the big surprise: buddy signaled ten minutes of deco. He might have dipped a little deeper than I had, one percent leaner nitrox blend, a different algorithm, etc. We had plenty of gas, even if one of us lost everything. So doing the extra five minutes is no big deal? Well, at that point my dry suit was leaking and during those long, cold extra five minutes I was cursing my buddy for the deviation from our plan, and an otherwise very nice dive had turned into something less.

Scenarios like this are easy to get into when pushing NDL's. It's really why basic technical training is recommended before making a dive like this that can appear relatively simple. ☺

 

[doctormike]

Scenarios like this are easy to get into when pushing NDL's. It's really why basic technical training is recommended before making a dive like this that can appear relatively simple. ☺

Yeah, that's a good point. If you are in the habit of doing dives right up to the NDL in 120 feet of cold water, and you are carrying enough gas to get you into deco, it's probably a good time to take the AN/DP training. If nothing else, it will let you spend more than 15 minutes at depth, which is a good thing by itself. If you are both already comfortable with doubles or sidemount, it sounds like a good set of training buddies!

 

[kafkaland]

Yeah, that's a good point. If you are in the habit of doing dives right up to the NDL in 120 feet of cold water, and you are carrying enough gas to get you into deco, it's probably a good time to take the AN/DP training. If nothing else, it will let you spend more than 15 minutes at depth, which is a good thing by itself. If you are both already comfortable with doubles or sidemount, it sounds like a good set of training buddies!

You bet. It's for these dives and also for the caves in Mexico. I finished full cave down there earlier this year, and now that I'm diving to thirds I'm struggling to stay out of deco on many dives. But finding a good AN/DP instructor who teaches this course in sidemount in the Great Lakes has not been easy. I prefer to do it here in my heavy sidemount configuration, with big steel tanks, Halcyon Contour harness and dry suit, as I think what I learn here will translate easier to warm water, Al tanks and Razor harness than the other way around. I first looked into this about a year ago, and had little luck, now I got a referral to an instructor in Canada who dives regularly a configuration similar to what I'm using, but scheduling something with him has so far been impossible. I may just have to give up on doing it here and take a trip to Florida, or just go the easy route and do it in Mexico and figure out the tank mounting etc. in my Great Lakes configuration on my own. (Sorry for derailing the thread...)

 

[doctormike]

(Sorry for derailing the thread...)

Hah! No worries, sounds like you have some great diving ahead of you.

 

[Jack Hammer]

You bet. It's for these dives and also for the caves in Mexico. I finished full cave down there earlier this year, and now that I'm diving to thirds I'm struggling to stay out of deco on many dives. But finding a good AN/DP instructor who teaches this course in sidemount in the Great Lakes has not been easy. I prefer to do it here in my heavy sidemount configuration, with big steel tanks, Halcyon Contour harness and dry suit, as I think what I learn here will translate easier to warm water, Al tanks and Razor harness than the other way around. I first looked into this about a year ago, and had little luck, now I got a referral to an instructor in Canada who dives regularly a configuration similar to what I'm using, but scheduling something with him has so far been impossible. I may just have to give up on doing it here and take a trip to Florida, or just go the easy route and do it in Mexico and figure out the tank mounting etc. in my Great Lakes configuration on my own. (Sorry for derailing the thread...)

Mike Ridgeway is a cave and deco instructor out of the Chicago area who is highly recommended. I believe he can/will teach it for sidemount