Doing 'Light Deco' as a recreational diver

[Daryl Morse]

Depends on the computer algorithm. I just ran 3 consecutive air dives on my GAP-RGBM dive planner to 130 ft for 10 min (not incl. descent time), 60 min SI's. I got 3 min of deco at 10 ft. during the last dive, which imo is not a big deal and more or less what I'd do anyway as a "safety stop." I don't know if Suunto's use 5 or 10 min for NDL at 130 ft but even repeating the profiles for 15 min BT I still got only 4-5 min of deco on the last dive. RGBM tends to be on the liberal side though for these types of profiles.

I did the same thing with the pc simulator that comes with my Apeks computer. I used 66 f/m for descent and 33 f/m for ascent. I ascended to 20 fsw for the deco/safety stop.

For the first dive, it went into deco after 8 minutes at 130 fsw, calling for a max of 2 minutes. Cleared deco in less than 2 min, and surfaced after 3 min safety stop. Did 60 min SI.

For the second dive, it went into deco at exactly the same point and cleared at the same rate. Did 60 min SI.

For the third dive, it went into deco at the same point, but obligation increased to 9 min total which decreased to 8 min by the time 20 fsw was reached.

I have compared this simulator to v-planner and found that it's more conservative.

I wouldn't ever to 2 repetitive dives to 130 fsw, let alone 3. When my computer calls for deco, I do it what it says just to keep it from locking me out, but I don't consider a few minutes of deco to be "real" deco (as in mandatory deco) because the Quantum is so conservative. If I was using a less conservative computer than the Quantum, it would be a different thing altogether.

 

[Daryl Morse]

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...

I find the Quantum to be too conservative and I dive with it at SF0. I wish it had a less conservative setting. My dive instructor compared his Quantum with an Oceanic during a wreck dive and found the Oceanic had something like 20 min of NDL when the Quantum was showing 5 min of NDL. That's a pretty substantial difference.

WRT Mexico, don't get the idea that they are dangerous. I found the DMs and boat operators to be very professional. They just weren't overly hung up about a couple of minutes of "lite deco".

 

[ArcticDiver]

Some models are older and more up to date than others. Decompression theory is still a lot of guesswork but it IS advancing.

Example being original navy tables vs newer navy tables with doppler factored in and so on.

The main ones these days are gradient factors on buhlmann (a crutch basically to allow Buhlmann to give deep stops) and VPM (B/BE currently as 'A' wasnt great).
Both these branches are more in thinking than the older style bend and mend that bring a diver shallow quickly then keep him there for ages (and totally ignore microbubble formation etc).

So yes, in my view some models are "better" than others. More specifically newer thinking i feel is safer than 20-30 year old models based on bending goats with no human input to adjust the theory.

I'm glad you said "...in my view..." because there are lots of theories but precious little proof regarding which algorithm is better than another, if any are. For awhile it was thought that the Bubble Theory answered all questions. It was reported on this site that some folks whose doppler showed bubbles and should have been bent but weren't.

Spend an hour or so scanning them many threads and posts on this subject. You will find lots of passion fired advocacy for this algorithm or than. But precious little analytical evidence supporting the idea that one is better than another. Plus, there is a fair amount of suspicion that such non-quantifiable factors as hydration may be more important than the specific algorithm use.

So "in my view":
-All dives are Deco Dives. Just that from experience some are less or more tolerant of pressure/gas changes than others.
-From what statistics are available(precious few) it really doesn't matter what generally accepted algorithm a diver follows as long as they do follow it. As far as I know no commercially available algoritm has been statistically shown to be more or less safe than any other.
-We really don't know enough to call one algorithm "conservative" and another "liberal". These are marketing terms that are the diving equivalent to "comfort food".

 

[matt_unique]

What makes one algorithm "better" than another?

As differentiated from merely making a dive longer or shorter; what makes one algorithm "more conservative" than another?

Is V-Planner more "accepted" than, say DecoPlanner or its' like?

Are any of the algorithms, however implemented in paper tables, topside computers, or take along computers any "safer" than another?

V-Planner, as on example, is definitely more accepted for deco planning than relying on recreational computers to "get you out" of a deco obligation.

--Matt

 

[jeckyll]

I find the Quantum to be too conservative and I dive with it at SF0. I wish it had a less conservative setting. My dive instructor compared his Quantum with an Oceanic during a wreck dive and found the Oceanic had something like 20 min of NDL when the Quantum was showing 5 min of NDL. That's a pretty substantial difference.
...

Initially I played with the Quantum a bit. Tried it on SF0, tried it on SF2. Then sat down and broke out the RDP.

Added 10 feet for cold water to the RDP, threw the thing into plan mode and played around until I got something that was close to the RDP + 10 for cold water. That's SF1. I don't mind it being more conservative, I try to multi level all my dives, if they are square I do extra time on the line.

With the way it's setup now, it seems very close to the Suunto's.

But most importantly, if I'm doing any diving that's closer to where my limits are, I'll planned the dives up front and the computer really is just a depth and time measuring device (hence my reference to the minimum deco tables earlier in the thread). I just can't bring myself to throw it into gauge mode. And in all fairness, when I'm making multiple dives, I use the thing to check what NDL it will give me for different depths before entering the water to ensure my plan isn't out to lunch

Bjorn

P.S.: I'm Canadian. I use the word "light" to mean the opposite of heavy. Not "lite".
"Lite" is for beer that other people drink

 

[ArcticDiver]

V-Planner, as on example, is definitely more accepted for deco planning than relying on recreational computers to "get you out" of a deco obligation.

--Matt

Again; it depends and is independent of any particular algorithm.

You are comparing an algorithm (V-Planner) to how an algorithm is implemented (computer). It depends on how the algorithm is implemented in a particular computer make and model as to what it will, or will not do. Some will as you post "'get you out' of a deco obligation" but will not allow you to plan a deco dive. I believe there are others that will let a person plan and execute a deco dive.

I suspect how an algorithm is implemented in a particular make and model computer is governed by the liability and market judgements as much as anything.

 

[Meng_Tze]

I suspect how an algorithm is implemented in a particular make and model computer is governed by the liability and market judgements as much as anything.

Yes it is. The manufacturer decides 'how smart' their users are and puts in 'safety' around the implementation of the algorithm. This is why you have two computers with the same algo, run two different profiles. Heck, look carefully at some manuals of computers and you will see some interesting algos: 'Modified Swiss' (probably Buhlman C with manufacturer fudge), Suunto 100, Suunto 50, VPM (in VR3, but not the same as vplanner), modified Haldanean.

It is entirely up to the manufacturer, don't be fooled in thinking that algo on paper is what you get as algo in a computer.

 

[redacted]

If I'm doing 4 or 5 dives a day, I want a conservative computer, which is why I use Suunto. I agree that 130' is a rec depth for me as well.

So do you use a different computer if your diving schedule is on the lighter side? I've found it is not too difficult to be more conservative when using a liberal computer. But it is pretty hard to be more liberal than a conservative computer.

 

[lamont]

Part of the issue being debated in this thread comes down to semantics.

There is no such thing as "light" deco. Or "lite" deco.

Lets call it what it is:

"Unanticipated" deco.

"Unexpected" deco.

"Unplanned" deco.

"Oops I crapped my pants" deco.

"I enjoy placing my phallus in a bass-o-matic" deco.

"This is what happens when we lose situational awareness" deco.

I'm actually considering the normal result of planning a recreational dive to the limits of the NDLs. Usually this would look like a dive plan of 30-35 mins between 90-110 with the max depth coming early in the profile on EAN32. Typically this pushes right against the NDLs on, at least, the Suunto Vyper that I used to use and I've seen 5 minutes of deco flashing on my computer as I ascend quite a lot, and it became planned.

This is long after DIRF, long after having stopped thinking of CESAs as an option, with good gas planning, with enough contigency gas to deal with more than a few minutes at depth and still deco an even higher obligation out with two divers. The ability to adequately hit stops on blue water ascents, etc. But not done with formal technical training.

So, is this kind of "decompression lite" acceptable in technically-minded divers who are not yet techncial divers? That is the question the way that I interpret it. I don't believe the question is if the average diver should be sitting down at 100 fsw on an Al80 with less than 500 psi with a mandatory deco ceiling showing on their computer and thinking everything is just peachy...

 

[Diver Dennis]

So do you use a different computer if your diving schedule is on the lighter side? I've found it is not too difficult to be more conservative when using a liberal computer. But it is pretty hard to be more liberal than a conservative computer.

No, I always use the same computers but my point was that I think you are better off starting with a conservative computer in case you end up doing more than just a couple dives a day. I don't find the "conservative" Suunto computers hinder my diving.