Deco diving without a written out dive plan?

[PfcAJ]

I don't think I need 4 computers. But, if (IF, I'm just asking IF) I have 2 and my buddy has 2, do we also need written/printed out tables on a slate or in wet notes? Or, at that point are tables excessive?

Asking it a different way: You and your buddy use V-Planner and work out a complete dive plan (profile, gas management, etc.) that you both agree to. Your buddy says "I'm not going to take a slate or notes. I'm just going to dive with 2 Petrels." What is your response to that? What concerns would you have about that?

I *just* gave an example outlining how easy it is for a computer to give you the wrong info. You think we didn't have a discussion about the difference between the table times and the computer generated times in the water? "Wtf is this box asking for 30 extra minutes compared to these tables? What's the variable we're missing? Oh, that's right, the descent gas was wrong in the computer."

For your example, if at least one of us has tables, I'd do the dive (depending on the dive).

 

[packrat12]

I'll give you an example: I did a dive recently where the computer did not match up with the tables. It wanted something like 30mins more deco. Why? I started the dive with the computer set to another gas. Back at deco, the reason for the difference became obvious. Moral of the story: The computer DOES have the potential for error. In this case, because of not pressing the right button, tables were king again.

PfcAJ - That is not a error of the computer but the user. The computer is giving the correct data. You failed to set it properly. The same thing could have happened during your preplanning and you select the wrong gas for the tables you made. Garbage in = Garbage out.

Stuartv - The use of pre-planning is critical for making sure gases and other aspects of the dive are 'doable'. Using 2 computers are acceptable to do deco with but a pre-plan is still necessary to accomplish a 'serious' dive safely. There is a good way of determining gear needs - One is none, two is one, three is two. If you need 1 of something, you need to bring 2. For deco phase, I need 2 methods of getting out of the water incase of failure. 1 Computer/ 1 BT or 2 Computer or 2 BT etc. There would be a slight risk for both computers to hang during a dive but I find that risk acceptable, especially for a high quality computer like SW. For light deco, I may not have a plan as I know from previous usages, I have enough gas with me, e.g. 1 stop to accomplish by deco safely.

 

[stuartv]

I *just* gave an example outlining how easy it is for a computer to give you the wrong info.

Yes, right. I got that. But, that was user error, not computer error, right? Not that I'm completely dismissing that. But, a narced human could mess up with tables, too, right? "Dang. I was diving 32% but I messed up and brought my tables for 23% and didn't notice when I was on the bottom looking up my ascent schedule."

Anyway, I think I understand your choice on the answer to my question. You would not do a deco dive without carrying tables - even if you do have 2 full blown tech computers - because of the possibility of human error in using the computers (the specific example being failing to set the gases correctly).

BTW, on your example, I would have thought you would catch an error like that well before getting to your deco. I have had the same problem several times now, thanks to a feature on my Atom where it resets to Air after 24 hours. At least twice now I have set the FO2 and gotten in the water within 20 minutes. Not long into the dive both times I noticed that my NDL on my Atom was quite a bit less than the NDL on my Petrel and before I went any further figured out why. Unfortunate timing on my first dive of the day compared to the end of my last dive the day before.

In your case, you forgot to set your gas correctly on your computer and you didn't notice until, if I understood correctly, you finished the dive and were ready to start your ascent? Does this qualify as a case of using equipment (tables) to solve a skills problem (not setting the computer AND not noticing until the end of the dive)? I'm not trying to be a dick or pick on you about it. I'm just wondering, really, if you think the correct protocol to adopt based on this incident is really "always carry tables"? What if your computer had been set wrong the other way and it gave you a an ascent that was only 5 or 10 minutes off but shorter than it should be? You might not even notice and then just blindly follow it, right?

Also, you said tables were king again. But did you really need to use tables to deal with that? Did you not have a buddy with a dive computer that was set correctly and working? Or, could you not have used Ratio Deco to get yourself to the surface safely?

Getting back to my original question... a diver gets in with 2 dive computers and an understanding of Ratio Deco. Even if they screwed up and had BOTH computers set to the wrong gas AND didn't realize it until the end of the dive, they could still get themselves to the surface safely using Ratio Deco, right? (Not trying to debate the validity of Ratio Deco itself here - I'm presuming that the diver knows how to use it and that it provides acceptably safe results when used correctly)

 

[fsardone]

There was a poll started by me on this ...
http://www.scubaboard.com/forums/t2...x/498512-how-do-you-manage-decompression.html

You might find some insight there.

cheers

Fabio

 

[PfcAJ]

Youre both correct. It WAS my error. The tables are there to provide a simple, reliable way of checking the not really simple device on your arm. Without the tables, there's nothing SOLID to reference against.

I'm not surprised I didn't notice it. I barely look at the bottom timer or computer during the descent phase of the dive. The computer wasn't and isn't a primary tool for me, and my buddy didn't use a computer on that dive.

RD doesn't work well on 100min bottom times.

 

[stuartv]

Stuartv - The use of pre-planning is critical for making sure gases and other aspects of the dive are 'doable'. Using 2 computers are acceptable to do deco with but a pre-plan is still necessary to accomplish a 'serious' dive safely.

Yes, I've said several times that I'm not talking about what you do for planning. I'm ONLY talking about whether you do the last step of actually writing out or printing your dive plan(s) and take them in the water with you.

There is a good way of determining gear needs - One is none, two is one, three is two. If you need 1 of something, you need to bring 2. For deco phase, I need 2 methods of getting out of the water incase of failure. 1 Computer/ 1 BT or 2 Computer or 2 BT etc. There would be a slight risk for both computers to hang during a dive but I find that risk acceptable, especially for a high quality computer like SW. For light deco, I may not have a plan as I know from previous usages, I have enough gas with me, e.g. 1 stop to accomplish by deco safely.

So I gather you do feel like it's okay to do the actual dive carrying 2 computers and not carrying actual written out plans. And in particular it would be okay if the computers were 2 completely different brands, thus virtually eliminating the chance that a hardware or firmware issue combined with any particular set of circumstances could cause both computers to hang up. But even if both were well known entities like Shearwaters it would be okay to be 2 of the same.

---------- Post added January 11th, 2016 at 05:03 PM ----------

Youre both correct. It WAS my error. The tables are there to provide a simple, reliable way of checking the not really simple device on your arm. Without the tables, there's nothing SOLID to reference against.

I'm not surprised I didn't notice it. I barely look at the bottom timer or computer during the descent phase of the dive. The computer wasn't and isn't a primary tool for me, and my buddy didn't use a computer on that dive.

RD doesn't work well on 100min bottom times.

I certainly understand why you took tables and if you only ever dive 1 computer, why you would always take them. So, if I'm inferring correctly, you think it would be a bad idea for someone to dive with 2 computers and no tables for the reason that they could screw up and do the dive (or a significant portion of it) with both computers set to the wrong gas. And then, without tables, they would be screwed.

And you're saying that it is more reliable for you to take the correct tables (you said you don't take tables for all gases, depths and times) for the specific set of gases you are using and the depths and time ranges you are likely to dive than for you to set your computer's gas correctly.

 

[packrat12]

Stuartv - Yes I do believe that you do not need a written deco schedule with 2 computers in use. As I have stated in other threads, once I start my ascent, my computers will hold my active deco schedule and with 2 computers, they will hold my backup. I will use gas considerations and time/depth limits from the pre-planning regardless. If I am really in a serious dive, I may carry tables as a 3rd failsafe if all else was to go bad.

 

[stuartv]

There was a poll started by me on this ...
http://www.scubaboard.com/forums/t2...x/498512-how-do-you-manage-decompression.html

You might find some insight there.

cheers

Fabio

Thanks, Fabio. I click the link and it says I don't have permission to access that page. It appears to be in the Tek2Tek forum, which I am not eligible to join yet. I haven't even finished AN/DP yet.

 

[PfcAJ]

I certainly understand why you took tables and if you only ever dive 1 computer, why you would always take them. So, if I'm inferring correctly, you think it would be a bad idea for someone to dive with 2 computers and no tables for the reason that they could screw up and do the dive (or a significant portion of it) with both computers set to the wrong gas. And then, without tables, they would be screwed.

And you're saying that it is more reliable for you to take the correct tables (you said you don't take tables for all gases, depths and times) for the specific set of gases you are using and the depths and time ranges you are likely to dive than for you to set your computer's gas correctly.

yea I think that's fairly accurate. I'm certainly less likely to grab the wrong tables than bop the wrong button on my computer, esp since our planning is so tables centric.

 

[decompression]

Depending on the dive, I bring several tables, loss of deco, ratio deco knowledge, petrel and cut profiles......too much?




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