Overshooting NDL and mandatory deco stops

[Lorenzoid]

It has been stated that a reason for using the Perdix is that it has a superior and more intuitive user interface. . . .

There are rather brilliant sets of menus within those two buttons. I have witnessed on a dive where a diver that didn't understand the gas definitions and selection menus started pushing the buttons underwater trying to get back to the basic dive screen and actually defined a gas as 41% nitrox, turned it on and switched to it in the middle of a dive. It is made easy to do this by this computer because it is assumed that you understand the computer and gives you the power to do it easily. She came to me at 100 feet and showed me a warning that she was exceeding her PPO limit even though she was diving air. She was having a hard time getting to a screen that made sense to her because she didn't really understand the computer beyond it's simple and easy to understand main screens. She was of course showing a much higher NDL at that point than she should have been because the computer thought she was on 41% nitrox.

GREAT point, Ray. The "simple and easy to understand main screens" are a double-edged sword. This whole thread touches on issues with Shearwater computers that have been the subject of much discussion in the past. If I recall, the suggestion has been brought up before that if it is assumed many Rec-only divers will not read the manual there should be more limits on what can be done in Rec mode.

 

[Efka76]

The biggest issue is that many divers who have fancy computers do not read manual. Instructor was telling me stories how people own Shearwater perdix, suunto eon core or steel computers in order to show off but do not have any clue what how to use them. Yes, these are recr divers.

I have opinion that if i have dive computer, car, photo camera, any electronic gadget, i always read manual in full and make sure that i understand how to use functions. Also, i am not a fan of upgrading for the sake of upgrade. Currently i own Cressi Newton which i used 100 percent functions and is fully sufficient for my dives. I can upgrade to shearwter perdix even tomorrow as cost is not a limiting factor for me, however, do not see the need as i do not do trimix or ccr diving.

 

[Doby45]

GREAT point, Ray. The "simple and easy to understand main screens" are a double-edged sword. This whole thread touches on issues with Shearwater computers that have been the subject of much discussion in the past. If I recall, the suggestion has been brought up before that if it is assumed many Rec-only divers will not read the manual there should be more limits on what can be done in Rec mode.

The simple easy to read main screens would be for people that are not changing anything. If that is done I think the Shearwaters are pretty much idiot proof in REC mode for NDL diving. If you go in and change things around which you have no understanding of, then the computer is about as much use on your wrist as a dinner plate. That is not a fault of the computer, that would be the diver needing to RTFM.

 

[Storker]

All deco should be planned for. There's simply no reason to get into deco without prior thought.

Of course. I was merely commenting on the difference between "be back at the safety stop with 500psi", usually with an Al80 (11L), and "be back at the safety stop with 50bar", no matter your tank size. That's some rather different safety margins. An Al80 with 500psi/35bar is barely 400 surface liters (and uncomfortably close to the error margin of an SPG), a 10L with 50bar is 500 surface liters and a 15L with 50 bar is 750 surface liters. I'm just a little surprised that the safety stop recommendations for basic OW divers are so different whan you look at the numbers.

 

[Charles2]

If a diver were at 100ft depth and for whatever reason lost track and overshot the NDL by say 2 minutes and started up then at what depth would the mandatory stop be and for how long? On air.

I just looked up your dive plan of 100 fsw for 2 minutes past NDL (i.e. 24 min. @ 100 fsw) on the NAUI AIR DIVE TABLES. You would be required 5 minutes of decompression at the 15' stop.

I assume if you hit the NDL on 32 nitrox it would end up being the same thing you were just at 100ft longer to get there.

Using the NAUI EAN 32 DIVE TABLE and a dive plan of 100 fsw for 2 minutes past NDL (i.e. 32 min @ 100 fsw) would require 7 minutes of decompression at the 15' stop.

I would expect your computer to be somewhere in those neighborhoods.

Be sure to plan your gas consumption accordingly. These stops are required, not just recommended.​

 

[Lorenzoid]

. . . If you go in and change things around which you have no understanding of, then the computer is about as much use on your wrist as a dinner plate. That is not a fault of the computer, that would be the diver needing to RTFM.

I agree, but the issue is how to help keep safe the people who inevitably will not RTFM. As Ray's anecdote shows, the Shearwaters do allow more things in Rec mode to be changed than other "Rec" computers, such as the Suunto Zoop. Despite it's wonderful Rec mode, the Perdix/Petrel is more than just another rec computer like the Zoop. Even in Rec mode, you really do need to know what you're doing with it.

 

[rsingler]

but the issue is how to help keep safe the people who inevitably will not RTFM

Why?

I feel zero obligation to answer the OP's question, when posted in the Advanced Forum.

 

[Lorenzoid]

Why?

I feel zero obligation to answer the OP's question, when posted in the Advanced Forum.

I wasn't addressing the OP's question. Mine was an off-topic comment about Shearwater's Rec Mode in view of the fact that some divers, even those who are "Advanced" as that term is commonly used, will never read up on how to use their computers. Feel free to delete it.

 

[rsingler]

It's been a good discussion of important issues. But as you implied, most of the answers were already in the manual. It's one thing to ask for clarification. It's another to ask ScubaBoard's generous members to do your homework for you.

 

[Dzydvl33]

I started diving in the early 90s when I was a teen... then some dumb teen choices, kids, drugs, life lol kept out of the water. When I returned at the beginning of this year it was a foriegn world filled with computers. I was lost. I did a bunch of homework on here and on the web.
#1 recommendation I would make for divers wondering "what if"s is get a dive simulator. If you go to DiveNav - Products you can get a class for your specific computer and then download Virtual Diving - Explore your Ocean to use your computer in real world situations. It has been amazing to help me understand stand what my computer is telling me.
For the "whys" I found these articles and a video that, I feel, have me a good understanding of what is going on with the gases I'm breathing and in my body. I WOULD STILL NOT DO A DECO DIVE WITHOUT PROPER TRAINING. I do feel better about handling myself in an overstay situation, although, with the knowledge I have found so far, I understand the importance of making a plan and sticking to it.

Happy & Safe Diving
Never stop learning.

Websites
So you want to buy a new computer?

Gradient Factors | Dive Rite

Decompression Theory - Part 1 - SDI | TDI | ERDI

Decompression Theory - Part 2 - SDI | TDI | ERDI

Decompression Theory Part 3- Bubble Counters - SDI | TDI | ERDI

Decompression Theory Pt 4 - SDI | TDI | ERDI


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