"Riding your Computer Up" vs. "Lite Deco"

[halocline]

The more conservative deco ascent gives more effective off-gassing than just a 3 minute mandatory stop for the exact same dive.

I can see that, but you really don't need to follow a more conservative computer's required deco plan to get the same (perceived) safety benefit. You just need to alter your dive behavior to maximize off gassing. To my knowledge, within recreational limits, this is achieved by spending longer at shallow stops. To me it doesn't matter whether my computer is telling me to do it or not. But again, my motivation is more about feeling better after a day of diving than about avoiding clinical DCS.

 

[redacted]

If you are diving with a group that allows or accepts that procedure, then no problem. Otherwise, you need to think about how your behavior might adversely effect others.

 

[dumpsterDiver]

You are diving natural reef right off the inlet in 115 ft? I am guessing? Possibly diving deeper stuff than normal and trying to stay in clear water? That is kinda deep for no redundancy and past what i consider light deco.

 

[lowviz]

I can see that, but you really don't need to follow a more conservative computer's required deco plan to get the same (perceived) safety benefit. You just need to alter your dive behavior to maximize off gassing. ...

Yes, I could alter my behavior. That is what I’m doing. On the first dive, that’s a pretty easy thing to do. But a conservative DC keeps track of everything and suggests a second dive based on the same level of conservatism as my first dive. It calculates everything based on the level of conservatism that I want to maintain.

It also remembers and rewards/penalizes me for what I actually did on the first dive. It is more than a convenience, I don't know how I would track all that. Sometimes, I’m quite surprised at those rewards/penalties.

 

[RainPilot]

With respect to diving two different algorithm computers, I know of some tech divers who have 2 different GF set on their 2 computers. One is what they want to do and have planned for, and the other for a "it's all gone wrong" moment when getting out of the water is priority. Some do it by changing GF in the dive where the DC allows.

I see no difference with doing the same in rec diving. If the conservative DC goes into light deco then I would adhere to it, knowing exactly where i could blow off that deco in the case of a recall, emergency etc. The principle of using two redundant systems and following the most conservative one is a well known and respected strategy. Utilizing the DC's this way makes the conservative one more of an ascent management tool than a deco-device if that makes sense...

The fact that one of them goes into deco should not be an issue, ask yourself "If I only had the aggressive DC would I still be in rec limits?"

Iff the answer is yes, then no worries. If not, you need to re-evaluate whether you are still in the rec realm or not, especially from an insurance / liability point of view.

 

[KenGordon]

I saw a good (meaning bad) example of what I would not call lite deco today on a recreation drift dive. Four divers plus guide. All lobstering and 1 also carrying a speargun. Sporty seas so the captain asked us to dive as a group. First dive was deepish. About 110 max. I floated at about 80 till I spotted a bug but 2 others dove mostly at depth. They had to have bumped into NDL limits. I had total about 5 minutes deco on the Petrel set for max VPM and cleared on ascent. Cressi never in deco.

Second dive max 115 and again two divers stayed low. We lose one diver early on but the other continued with us. I had about 5 minutes into deco when I went up to hang around 30. Eric and the guide came up shortly after and we hit the safety stop. I now have just the 3 minute safety stop on my Cressi and the Petrel cleared. Finely the last diver joins us. Sure enough he swims over to the guide and shows him his computer. The guide signals deco and 15 minutes then tries to tell him what to do. Several times throughout that stop the diver in deco would show his computer to the guide and the guide would signal level and time.

Fortunately Eric and I had plenty of gas so we chose to stay with the diver and guide. It turned into a 22 minute safety stop. On the boat I found out the diver was diving Oceanic and I believe it was DSAT.

That diver is not how I would define lite deco.

This is a mistake by that diver. If he wasn't doing it deliberately I don't think that is the behaviour which is being discussed on this thread. My understanding is that this is about deliberately doing short, back gas stops.

Of course it illustrates an extra peril, not paying attention. If you are planning for 10 minutes of stops and get distracted and end up with 30 minutes then you are at significant risk of your tea being cold and the rest of the divers having eaten all the cake by the time you get back on the boat.

 

[KenGordon]

I have a hard time believing that DSAT would be more conservative than VPM, or, particularly Cressi RGBM. There must be more to this story, his profile, computer settings, something. The Cressi RGBM is among the most conservative of the commercially available decompression algorithms. DSAT is 2nd to Cochran as the most liberal. There's more to every story....

I think you are extrapolating no stop times to stop times. Just because a computer gives long NDL times does not mean it will give short stops.

 

[scubadada]

I saw a good (meaning bad) example of what I would not call lite deco today on a recreation drift dive. Four divers plus guide. All lobstering and 1 also carrying a speargun. Sporty seas so the captain asked us to dive as a group. First dive was deepish. About 110 max. I floated at about 80 till I spotted a bug but 2 others dove mostly at depth. They had to have bumped into NDL limits. I had total about 5 minutes deco on the Petrel set for max VPM and cleared on ascent. Cressi never in deco.

Second dive max 115 and again two divers stayed low. We lose one diver early on but the other continued with us. I had about 5 minutes into deco when I went up to hang around 30. Eric and the guide came up shortly after and we hit the safety stop. I now have just the 3 minute safety stop on my Cressi and the Petrel cleared. Finely the last diver joins us. Sure enough he swims over to the guide and shows him his computer. The guide signals deco and 15 minutes then tries to tell him what to do. Several times throughout that stop the diver in deco would show his computer to the guide and the guide would signal level and time.

Fortunately Eric and I had plenty of gas so we chose to stay with the diver and guide. It turned into a 22 minute safety stop. On the boat I found out the diver was diving Oceanic and I believe it was DSAT.

That diver is not how I would define lite deco.

Sorry, did not realize the diver had significantly different dive profiles. Not planning, and being surprised by a relatively long obligation, is not light deco, it's stupidity. Good thing the diver had assistance and enough gas to do the deco. Sounds like the diver may not have been sufficiently familiar with the dive computer either.

In October, we did a dive on the Castor. One of the divers was on air, but agreed that it was a good 1st dive and discussed the limited bottom time with the captain. One of the other divers found him at the safety stop with 25 minutes of deco on a nearly empty AL80. Apparently, he was very surprised when the deco was pointed out to him. He briefly shared air with 2 divers while another went up, switched out tanks, and completed the deco with him. Obviously, he sat out the 2nd dive while we decided to do a 2nd dive on the Castor. He was very lucky others assisted him, who knows what would have happened otherwise.

Light deco is planned, relatively short deco, with more than adequate gas available. Stupidity, ignorance, and/or carelessness, is something else altogether and is not what we started off discussing.

 

[redacted]

Awap. Let me try and explain it as I practice it. The conservative dive computer tells me, based on more then just bottom time, where that conservative line in the sand lands. Then I can make a judgement call based on many factors if I follow that conservative line and not cross it, or if I have a little leeway to cross the conservative NDL line but then use other factors as an added safety margin, such as ascent but also longer and now manditory safety/deco stops, longer SI, shorter second dive, etc.

Yes, I could modify my Petrel, even during a dive, to give me almost any dive I want but then that line in the sand is blurred. If I have one computer set conservative then I always know right where I stand in relationship to that line and can make more informed choices about the rest.

Remember, conservative computers are not just about shorter bottom times, in fact they may give longer dive times on that first dive, but rather are mutifactorial in calculating NDL's

This works for me. It may not work for you.

So you are really getting multiple lines in the sand and choose to use the most conservative. But then you have no problem crossing that first line because you know it is conservative. So, where does that leave you in relation to the alternative lines you have that you could!d use. That is, have you really put a hard ceiling over your head during a recreational dive or are you actually pretending that ceiling is there so you can be guided through a more conservative ascent. Why not run your bottom time on a more liberal algorithm, honor that limit, and then switch to a more conservative algorithm as you begin your ascent,. That way you can enjoy whatever advantage there may be in the more conservative ascent profile with little risk of actually incurring a hard ceiling. I do suspect that a deep stop could push the liberal algorithm into deco but you could even check that on the fly if a problem arises.

 

[redacted]

The more conservative deco ascent gives more effective off-gassing than just a 3 minute mandatory stop for the exact same dive.

I do not think that is entirely correct. Unless the risk of surfacing is too high, the most effective place to off-gas is at the surface. Artificially elevating the risk of surfacing does not really change that.