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

[lowviz]

OT, I always thought 'riding the computer' was on the inside of the calculated NDL (ie, staying at a depth until the NDL said <5min) to maximize your dive w/out going into deco ...//...

You are correct, but there are two very different ways to do this. The first is to stay on the bottom until you hit your NDL and then begin a direct ascent. The second way is to "ride your computer" on an extended ascent so that you are always showing that you are at the limit of your NDL. (Read the first paragraph in this post: Doing 'Light Deco' as a recreational diver)

The first scenario would be for a tied-in wreck dive and the second is common on reef dives. Neither violates NDL and puts you into deco. If you did either of those dives with a very conservative algorithm/DC you won't be down very long compared to most other divers. If you do use a high level of conservatism and do lite deco, then you are forced into a direct ascent and have to follow the required stops. I see this as far safer and better understood in terms of degassing. [/OPINION]

 

[Storker]

there are two very different ways to do this. The first is to stay on the bottom until you hit your NDL and then begin a direct ascent. The second way is to "ride your computer" on an extended ascent so that you are always showing that you are at the limit of your NDL.

An interesting datapoint: I use a Suunto, and as we all know ( ) Suuntos are unacceptably conservative. Last summer I did a couple of dives in France, with a guide as is normal for tourist diving. Our second dive for the day was an almost perfect triangular profile with a max depth of just a little more than 30m. A typical "riding the computer" dive. My (way too conservative as we all know) Suunto never told me I was in deco, but when I downloaded the dive to my PC and re-analyzed the dive I was at times well into deco according to a Buhlmann 40/70 GF model.

Now, was I in deco, or wasn't I? I've made the conscious choice to follow the algorithm of my computer, so at any time during the dive I could have made a direct ascent to the surface. If I'd been using a computer which allowed me to set my GFs to e.g. 40/70, I wouldn't have been able to do that. Since I'm a fairly average rec diver, I just follow my computer, and if I have to make an emergency ascent I'll probably opt for some time on O2 if I were to do a fast emergency ascent when my computer showed a small remaining NDL. However, if that ascent had been controlled and according to recommendations, I wouldn't have bothered with the O2. But I might well be more than usually aware of DCS symptoms...

 

[lowviz]

I see them as "just about right". Welcome to the darker side of the fence...

 

[scubadada]

An interesting datapoint: I use a Suunto, and as we all know ( ) Suuntos are unacceptably conservative. Last summer I did a couple of dives in France, with a guide as is normal for tourist diving. Our second dive for the day was an almost perfect triangular profile with a max depth of just a little more than 30m. A typical "riding the computer" dive. My (way too conservative as we all know) Suunto never told me I was in deco, but when I downloaded the dive to my PC and re-analyzed the dive I was at times well into deco according to a Buhlmann 40/70 GF model.

Now, was I in deco, or wasn't I? I've made the conscious choice to follow the algorithm of my computer, so at any time during the dive I could have made a direct ascent to the surface. If I'd been using a computer which allowed me to set my GFs to e.g. 40/70, I wouldn't have been able to do that. Since I'm a fairly average rec diver, I just follow my computer, and if I have to make an emergency ascent I'll probably opt for some time on O2 if I were to do a fast emergency ascent when my computer showed a small remaining NDL. However, if that ascent had been controlled and according to recommendations, I wouldn't have bothered with the O2. But I might well be more than usually aware of DCS symptoms...

40/70 is extremely conservative for recreational diving

 

[boulderjohn]

My (way too conservative as we all know) Suunto never told me I was in deco, but when I downloaded the dive to my PC and re-analyzed the dive I was at times well into deco according to a Buhlmann 40/70 GF model.

Now, was I in deco, or wasn't I? I've made the conscious choice to follow the algorithm of my computer, so at any time during the dive I could have made a direct ascent to the surface. If I'd been using a computer which allowed me to set my GFs to e.g. 40/70, I wouldn't have been able to do that.

That was part of what I was trying to say with my first post. If you are following a computer using Buhlmann with GFs of 4-/70. you will indeed go into deco before anyone else, but it will only call for a one minute stop at that point.

 

[lowviz]

...//... If I'd been using a computer which allowed me to set my GFs to e.g. 40/70, I wouldn't have been able to do that. ...

Yes, you would. Just blow off the lite deco requirement.

That is a rather sobering thing to do, but still much safer than flying an aggressive DC. Don't confuse lite/light deco with real deco.

Yet another fuzzy line...

 

[scubadada]

I find the discussion of different flavors of light deco to be particularly interesting. I dive an Oceanic VT3 running DSAT as my primary computer and a Dive Rite Nitek Q running Buhlmann ZHL16C, GFs x/90-100 as my backup. I take 5-10 minutes of deco seriously and would generally not consider blowing off the obligation. If I were diving a significantly more conservative computer or running @Storker GF 40/70, I might be considerably less concerned.

 

[DevonDiver]

40/70 is extremely conservative for recreational diving

For a first dive maybe... but there a few algorithms that get this conservative on repetitive dives.

In comparison with Suunto RGBM, I find that GFhi ~90+ provides comparative bottom time on the 1st dive of a series. For a second dive, you'd need to drop GFhi down to ~70ish.

I do this routinely, check partner's bottom time on reaching the bottom, adjust my GFhi to match. It helps my supervisory situational awareness, when students are likely to be task loaded. I use Shearwater's GF99 info to track my own preferences and keep things clean.

 

[uncfnp]

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.

 

[scubadada]

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....