Going into Deco as Rec Diver

[Blackcrusader]

I'm diving in Providencia, Colombia and today I went into Deco. Don't know how because I was watching my no deco time and it was fine then all of a sudden I saw that I was in Deco. I'm guessing that it was a mixture of all the sharks (there were 5-6 of them swimming all around us - spectacular) and maybe getting narced. Wondering how common is it to hit deco as a rec diver. I've come close within a few minutes but have always paid close attention, including the first day when we followed a 43.3m dive with another deep dive of about 25m.

The ggod news is that I now know what deco looks like on my Mares Nemo Wide.

Got a thread on this here below. Learn what your DC is telling you.

V

Thread 'Exceeding the NDL during recreation diving'

Aug 31, 2024

Hello, I am a recreational diver with an AOW license and I use a Garmin Descent 3. I can't understand the difference between using a medium conservatism profile, going beyond the NDL limits but ascending slowly, following the computer's instructions—in essence, the decompression happens during the ascent since we always ascend very slowly—and using an aggressive conservatism profile without exceeding the NDL. Essentially, this seems like self-deception, and with the aggressive profile, we don't see deco diving on the graph. Could you please tell me if I can continue using the medium...

• Vbukin
• deco dnl
• Replies: 102
• Forum: Advanced Scuba

• 

 

[Centrals]

V

Thread 'Exceeding the NDL during recreation diving'

Aug 31, 2024

Hello, I am a recreational diver with an AOW license and I use a Garmin Descent 3. I can't understand the difference between using a medium conservatism profile, going beyond the NDL limits but ascending slowly, following the computer's instructions—in essence, the decompression happens during the ascent since we always ascend very slowly—and using an aggressive conservatism profile without exceeding the NDL. Essentially, this seems like self-deception, and with the aggressive profile, we don't see deco diving on the graph. Could you please tell me if I can continue using the medium...

• Vbukin
• deco dnl
• Replies: 102
• Forum: Advanced Scuba

• 

Plenty of divers simply do not understand the various algorithms use in different computers. They blame the computer(algorithm) rather themselves. And you probably is one of them.

 

[DiveLikeAMuppet]

I've come close within a few minutes but have always paid close attention, including the first day when we followed a 43.3m dive with another deep dive of about 25m.

I would suspect that you are in the blurry area between sports and technical diving (both are recreational hobby diving …) If you dive to 43 meters, it might be good to review your gas planning, redundancy and such. 43 meters is pretty far away from home if you were on a single cylinder and trained with just mainstream agencies (not CMAS/BSAC that introduce these topics earlier).

E.g. I wouldn’t be concerned about few minutes of deco but I would start thinking whether you had enough gas to get yourself and your buddy home.

 

[Diver-Drex]

The root cause is not the algorithm. It is ‘not paying attention’. If you are not paying attention to NDL and can’t stay within it, you almost certainly are not paying attention to your SPG. So when you have an unplanned ‘surprise’ deco stop, you’re likely low on gas.

The argument that computers are conservative and it’s probably not ‘real deco’ does not make sense. Is it one minute conservative? Three minutes conservative? How many minutes of deco is just an overly conservative computer that you can just ignore?

What about a gas loss and a contingency plan to have something to breathe during that deco that you don’t really think you need?

Using MultiDeco: GF 100/100, SAC 6.8

80fsw for 35min gives a 3:00 stop at 20fsw. This takes 84cf to complete. So if you’re diving an AL80, which is most likely, you don’t have enough gas to complete the stop. GF is 100/100, so is there conservatism you can just ignore? And maybe it was cold or you were dehydrated and it isn’t conservative enough.

 

[Miyaru]

...

The good news is that I now know what deco looks like on my Mares Nemo Wide.

Excellent! The next step is understanding what your computer is telling you.

Your computer has a pressure sensor to calculate the depth, a clock to determine your divetime and software to calculate your on- and off-gassing (and thus, your NDL) continuously during the dive. It's a true-or-false calculation that does not take the following into consideration:

• your age and fitness level
• if your body feels cold or comfortably warm throughout the dive
• if the dive is easy or strenuous

and there are many other factors that influence your on/off-gassing. Your computer can handle true-or-false, but for your body there is a grey area in between that true and false.

During your dive, you were surprised by what your computer was telling you.
You can dive way more relaxed if you can predict what your computer is going to tell you.

To achieve that, find a (technical) instructor that can teach you how to dive beyond the recreational limit. With the correct mindset and knowledge, your computer won't surprise you again.

 

[scubadada]

Hi @Jafo19D

I've never understood how divers can become low on air or exceed deco without being aware of it. Pay attention.

You should exceed NDL and enter deco only on purpose, knowing that you have the gas to fulfill your obligation. Light deco does not require much additional gas. Ten minutes at 15 feet (4.6 m) with an RMV of 0.5 cu ft/min (14.2 L/min) requires about 7.3 cu ft (204 L) of gas or 283 psi (19.5 bar) from an AL80. A 3 min safety stop requires 2.2 cu ft (62 L) or 85 psi (5.9 bar). Much of my diving is solo, I carry redundant gas.

 

[DreadnoughtNH]

I'm diving in Providencia, Colombia and today I went into Deco. Don't know how because I was watching my no deco time and it was fine then all of a sudden I saw that I was in Deco. I'm guessing that it was a mixture of all the sharks (there were 5-6 of them swimming all around us - spectacular) and maybe getting narced. Wondering how common is it to hit deco as a rec diver. I've come close within a few minutes but have always paid close attention, including the first day when we followed a 43.3m dive with another deep dive of about 25m.

The ggod news is that I now know what deco looks like on my Mares Nemo Wide.

Echoing the general theme here, I doubt it was a lack of attention or narcosis, but rather a computer algorithm. The more conservative your algorithm, the more likely it will put you on a deco stop or an extended safety stop. My Shearwater does this occasionally, and my Cressi Leonardo did it routinely.
My $0.02: trust your computer; you bought it for a reason. If you have the gas, perform the deco stop or the extended safety stop. It won't hurt you.

 

[Diver-Drex]

Echoing the general theme here, I doubt it was a lack of attention or narcosis, but rather a computer algorithm. The more conservative your algorithm, the more likely it will put you on a deco stop or an extended safety stop. My Shearwater does this occasionally, and my Cressi Leonardo did it routinely.
My $0.02: trust your computer; you bought it for a reason. If you have the gas, perform the deco stop or the extended safety stop. It won't hurt you.

Trying to understand how you don’t think lack of attention has anything to do with this. Did the computer jump from 5min NDL remaining to a deco obligation on its own? Or did the diver forget to look at the computer for several minutes and then realize they overstayed the NDL? The diver stated they were distracted by sharks.

I agree with trusting your instruments. If it says you have deco, you need to clear it. But trust doesn’t matter if you aren’t looking at them in the first place.

 

[ROUS]

I've done it one time and I'm to blame. I was on dive 2 of 2 one morning and it was in a shallow area on top of the Great Cayman Wall. My (21%) air was lasting forever and I was having great fun filming some angelfish at play. The viz was spectacular, the marine life plentiful, and the dive guide was in no hurry to end the dive. At about an hour and a half of dive time, I felt my computer wrist vibrating urgently and the device told me to immediately report to some depth (can't remember). I was shocked. I shut down the camera, pointed to my computer for the guide, and headed up. The moment that I got to the prescribed depth, the Peregrine said that I was now fine and all was well. I certainly spooked myself though.

 

[MICHIGAN DIVER]

Thanks for comments above, I am in similar situation and had a question about tech classes. I am about 3 years 200 or so dives in. I was asked if I wanted to start tech classes but slow to get there mainly due to replacing so much equipment. That will take some time and $$. Anyone have any experience with the SSI extended range classes as an intro to tech type class. I have an opportunity to do this with a friend quite a bit cheaper more as a learning step than an actual jump into advanced type tech diving. Thanks