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

[lowviz]

A recent pony thread got me to thinking back to an amazing thread from days gone by, can't think of any search terms, fuzzy recollection... Yes! Just found it! Doing 'Light Deco' as a recreational diver

Please read posts 1, 16, and 31. :snicker: Do that and you will most likely end up reading it in its entirety.

So, for you recreational divers who do actually plan for and dive "light" deco: What do YOU consider the end of "light deco" to be?

For me, it is measured in minutes. 15.

Please stay within the TOS, but "gloves off" is fine with the OP...

 

[MXGratefulDiver]

I do what I call "light deco" commonly. For me it's usually on a dive profile where I'm spending a lot of time relatively deep (3-4.5 ata) and exceed NDL, but I'm planning a long, slow upslope ascent that will have me out of deco by the time I get to a shallower depth where I'm planning to spend some considerable time before anyway.

I differentiate "light deco" as meaning (a) going a few minutes past NDL is part of the plan, (b) I have both plenty of gas in my main tank(s) and adequate reserves in my backup to honor that deco if I should have to, (c) I'm planning to spend a considerable portion of the dive relatively shallow ... typically somewhere in the 2-2.5 ata depths where my deco obligation will clear before I head shallower, and (d) I don't feel any particular need to bring an O2 bottle.

As long as you have what you need to honor the obligation, it ain't rocket surgery.

Oh, and about that computer ... the only numbers I really need are average depth and elapsed time. The NDL number is really more for a sanity check ... and when in doubt, a few extra minutes at 20 feet never hurts.

... Bob (Grateful Diver)

 

[RyanT]

All right lowviz, gloves are off....here it is! Just kidding.

Before I embarked on technical training, the majority of my dives probably fell into this "light deco" category. When I was doing this most actively, it was the early-mid 90s so nitrox had not really caught on (at least in my area), and there was virtually no public information available on using oxygen or EAN for deco. So, the vast majority of my dives and deco were just done on air. We'd just go out and pick sites at random and dive them on a single AL 80. A very typical profile for me was 130' for 10-12 min of bottom time and a total run time of maybe 28-30 min. Most of my 15' hangs were under 10 minutes and I let my Orca EDGE calculate the dive for me. The longest hang I ever had was 30 min when I messed up. I just dove too many deep repetitive "light deco" dives that day and was a little surprised on my last dive when my computer gave me a much longer hang than expected. That experience and subsequent training taught me that I really like dive planning!!!

 

[Storker]

[not deco trained]
IME there's a rather fundamental difference between someone who's deco trained and has a good grasp of the consequences of not being able to go directly to the surface at any time during the dive, and someone (like me) who's not and doesn't properly realize the consequences of being in that situation. Including - particularly - the need for having a sufficient amount of breathing gas if for some reason you deviate from your dive plan.

If the former chooses to indulge in "light deco" - whatever that is, including clearing your deco obligation on your way up - that's an informed decision. Consenting adults and all that. OTOH, I shudder just a little when I hear of people exceeding no-stop limits without any gas plan or sufficient gas reserves to handle the consequences of a few minutes more at max depth if the brown stuff should interact with the rotating ventilation device.

 

[lowviz]

...//... there's a rather fundamental difference between someone who's deco trained and has a good grasp of the consequences of not being able to go directly to the surface at any time during the dive, and someone (like me) who's not and doesn't properly realize the consequences of being in that situation. ...

That kind of teases out my point. I see light deco as both planned (wrt gas) AND something that can be messed up without people, all of sudden, starting to say nice things about me...

 

[mdb]

I do what I call "light deco" commonly. For me it's usually on a dive profile where I'm spending a lot of time relatively deep and exceed NDL, but I'm planning a long, slow upslope ascent that will have me out of deco by the time I get to a given depth (usually in the 30-40 foot range, depending on the dive site) where I'm planning to spend some considerable time before heading shallower.

I differentiate "light deco" as meaning (a) going a few minutes past NDL is part of the plan, (b) I have both plenty of gas in my main tank and adequate reserves in my backup to honor that deco if I should have to, (c) I'm planning to spend a considerable portion of the dive relatively shallow ... typically somewhere in the 2-2.5 ata depths where my deco obligation will clear before I head shallower, and (d) I don't feel any particular need to bring an O2 bottle.

As long as you have what you need to honor the obligation, it ain't rocket surgery.

Oh, and about that computer ... the only numbers I really need are average depth and elapsed time. The NDL number is really more for a sanity check ... and when in doubt, a few extra minutes at 20 feet never hurts.

... Bob (Grateful Diver)

Nice post Bob.

Sane policy.

I have tried to employ a similar approach for many years.

I do not dive as deep these days, 80-120 FSW depending on where it is and what is there.
I do like to stick around if there are interesting critters so it is not drop and go; more stop and stay.

I always dive with a gas plan and plenty of reserve. I've had some past experiences where I did
not properly plan-I will not repeat them, way too old.

A slow controlled ascent seems to clear the Deco obligation below 40 FSW and then a quiet stop at
20 or so feet adds a bit of a safety margin.

 

[2airishuman]

I believe there's a class for that. Called "Tec 40" if I'm not mistaken.

So, this "lite deco" of which you speak. Do you carry enough redundant gas to meet any deco obligation you anticipate incurring?

What happens if you run into delays immediately prior to your planned ascent point?

 

[Storker]

I see light deco as both planned (wrt gas) AND something that can be messed up without people, all of sudden, starting to say nice things about me...

Just keep your DAN insurance current and make sure you're not too far way from the nearest chamber...

 

[tbone1004]

obviously not in the normal division of recreational diver anymore, but here is my personal definition of "light deco"

light deco for me is a deco obligation where the risks/rewards of doing staged/accelerated decompression is not worth it. Typically that is in the vicinity of 15 mins and corresponds to whether or not I feel the need to dive doubles/sidemount.

Most of the time for me, going to 50/50, 80/20, 100% whatever O2 and carrying the extra bottle is not worth saving 10 minutes of decompression. Depending on conditions, that may go up or down. In caves, I will almost always take an O2 bottle with me if planned depth is deeper than 60ft or so. It is pretty inconsequential to bring a 30 or 40, and even if I'm only doing a 3 minute safety stop, doing it on O2 doesn't hurt. Bottle is staged, dropped off quickly, and the surface conditions are easy.

In OW, I'll avoid that extra bottle as long as possible because I have to carry it with me, so I'll do planned deco on backgas up to a point, and that point will move depending on the dive profile and conditions. Cold, blue water, rough seas, etc. decompression? I'll probably bring that bottle after about 8 minutes of planned deco on backgas. I'll be doing at least 3-5 minutes to stabilize everything anyway if it was an NDL, so grabbing a small O2 bottle is worth it to get out of there quickly. Warm water with a reef or something interesting to look at? I'll stay on backgas because it gives more depth flexibility if there are pretty things to look at, less logistics concerns, and less risk.

 

[DevonDiver]

I do 'lite deco' very regularly - typically defined by using very conservative algorithm settings (Bühlmann ZH-L16) to give me very 'clean' surfacing. Even on dives where I don't exceed an NDL, I'll use the 'GF99' function on my Shearwater to determine a shallow stops curve that makes use higher differentials to raise off-gassing efficiency.

I approach every dive like a tech dive, and peetty much only ever dive sidemount or doubles, so it's really no sweat to ensure basic precision planning is always in effect regarding gas management, redundancy etc.

What I don't do is push my computer to the max and rely on 'experience' to hope that I'll avoid the consequences (formal stops) - so called 'riding' the computer up.

There's a number of reasons for this. Firstly, it takes some very significant experience to predict, with real confidence, that stops will clear on ascent. One has to fully understand the parameters of the algorithm used and how that applies to their relevant diving history.

Secondly, slow ascents may avoid fornal stops, but still prohibit direct access to the surface. An overhead limit is still in effect... and the necessary time-to-surface still necessitates resolution of all problems en-situ.

Lastly, I don't believe that a slow ascent offers the same decompression efficiency as a properly 'curved' ascent that maximises the time spent at greater differential to promote effective diffusion of inert gas from the body.

I've encountered this occasionally, where 'recreational divers' are pushing bottom times on dives in the 130-145ft (40-45m) range. I'll whisk past them on a 10m /min ascent rate en-route to formal stops, only to see them overtake me in the shallow phase and exit the water sooner.

Based on comparable total ascent (deco) times... they've forgone effective decompression at beneficial gradients purely to sustain the 'illusion' of maintaining a 'recreational' profile without formal stops.