Deco diving without a written out dive plan?

[stuartv]

Would you ever do a deco dive without a dive plan and contingencies written out on a slate or in wet notes?


I'm not planning to do this. I just want to know what you experienced folks think about the general subject. Or, to put it another way, instead of just blindly doing it the way I was trained, I want to learn why 2 computers and no written plan is bad. Assuming it is.

I have read numerous posts from people who say they do deco diving and don't carry a computer at all. Just their written dive plans and a depth gauge and bottom timer (and, presumably, backup depth gauge and bottom timer).

My current training is to dive with written plans and a depth gauge/bottom timer (generally in the form of a Rec computer in Gauge mode) and a tech computer. If the tech computer fails, fall back on the written plan and gauges. We're also going to be taught Ratio Deco at our next classroom session so we have a way to handle contingencies that fall outside of our written out contingency plans.

What I am really curious about is if anyone thinks it is acceptable to know Ratio Deco (for "just in case") and dive with two fully capable tech computers and no written out plan?

On initial consideration, it seems like diving with 2 Petrels and no written out plan is no more risky than diving with written plans and 2 sets of gauges (e.g. Rec DC in gauge mode or Xen Bottom Timer). Maybe even safer, since the computers will accommodate any contingency versus written out plans which will have a limited number of contingencies that can be written out and carried along.

If both your computers crap out, you're screwed. But, if both your Xen bottom timers crap out aren't you equally screwed? And is one really more likely than the other?

If both your devices (PDC or bottom timer) crap out, you don't have a way to follow your written out dive plan anyway, right? Your choices become, either, follow your buddy (who, presumably, has the same dive plan as you), or use your buddy's gauge/computer to give you time and depth and follow your own written plan. In that scenario, aren't you really going to just follow your buddy and his computer (maybe adding a few minutes on the way up to be conservative)?

Or is the only really safe plan to dive with a computer (e.g. a Petrel), a mechanical watch for your bottom time, a brass and glass mechanical depth gauge, and a written out set of dive plans? Or, to be TRULY safe, two mechanical timers, two mechanical depth gauges, and 2 sets of written out plans stored in two different places on your person?

Thanks for any insight and wisdom y'all can share.

---------- Post added January 11th, 2016 at 02:13 PM ----------

ps. To be clear, I'm not talking about what you do before you get in the water. It seems obvious to me that even if you dive 2 Petrels and no written out plan, you would still do all the same dive planning ahead of time to know your expected dive profile, gas consumption, etc.. I'm only asking about taking the final step of writing (or printing) the calculated dive plan and carrying it with you in the water.

 

[PfcAJ]

Imo a written plan is pretty important. Knowing your deco obligation and the relationship between deco time and bottom time/depth before you get in the water will prevent you from outrunning your deco gas or dive time constraints.

I dive with 1 bottom timer/computer. My buddy has the other. We do the same dive with the same gases and have the same ascent schedule.

Also, just having a few contingency plans is silly. Sit down at a computer, open excel, and make yourself some dive tables, then run over to kinkos and laminate them.

 

[stuartv]

Imo a written plan is pretty important. Knowing your deco obligation and the relationship between deco time and bottom time/depth before you get in the water will prevent you from outrunning your deco gas or dive time constraints.

Yes. I specified that one would still do the same planning before getting in the water. It's just whether you write/print out the plans and take them in the water with you.

I dive with 1 bottom timer/computer. My buddy has the other. We do the same dive with the same gases and have the same ascent schedule.

Also, just having a few contingency plans is silly. Sit down at a computer, open excel, and make yourself some dive tables, then run over to kinkos and laminate them.

Are you saying you dive with only one device? A bottom timer/computer (not sure what that means - a DC in gauge mode?)? Or you dive with a bottom timer (i.e. a device that shows depth and dive time) AND a computer?

And I'm not sure what you mean about contingency plans. My training has been to do a dive plan, a +1* depth contingency plan, a +1 time contingency plan, and a lost-deco gas plan. Then, print or write those out and take them in the water. Lost deco gas would normally be obviated by a plan that ensures each diver carries double the needed deco gas.

So, normally, by training, I would get in the water with 1 dive plan and 2 contingency plans written/printed out and affixed to a wrist slate or in wet notes. Are you saying I need to carry a greater number of contingency plans in the water with me?


* +1 in this context does not mean +1 foot or +1 minute. It means +1 unit of whatever size makes sense. Often it would be +5 or +10 feet and +5 or +10 minutes.

 

[Patoux01]

My training has been to do a dive plan, a +1* depth contingency plan, a +1 time contingency plan, and a lost-deco gas plan.

If those are all, I'd quickly run to your instructor and ask for a refund...

As far as I'm concerned with your first sentence, I did a ~20 minute (air) deco dive with a simple computer, no written plan, nothing. On some dives, common sense is a good enough tool as backup (eg the Coolidge in Vanuatu) for your deco.

 

[stuartv]

If those are all, I'd quickly run to your instructor and ask for a refund...

What other written plans should I take in the water with me?

 

[PfcAJ]

Yes. I specified that one would still do the same planning before getting in the water. It's just whether you write/print out the plans and take them in the water with you.




Are you saying you dive with only one device? A bottom timer/computer (not sure what that means - a DC in gauge mode?)? Or you dive with a bottom timer (i.e. a device that shows depth and dive time) AND a computer?

And I'm not sure what you mean about contingency plans. My training has been to do a dive plan, a +1* depth contingency plan, a +1 time contingency plan, and a lost-deco gas plan. Then, print or write those out and take them in the water. Lost deco gas would normally be obviated by a plan that ensures each diver carries double the needed deco gas.

So, normally, by training, I would get in the water with 1 dive plan and 2 contingency plans written/printed out and affixed to a wrist slate or in wet notes. Are you saying I need to carry a greater number of contingency plans in the water with me?


* +1 in this context does not mean +1 foot or +1 minute. It means +1 unit of whatever size makes sense. Often it would be +5 or +10 feet and +5 or +10 minutes.

One computer or one bottom timer for me. No real need for more since my buddy has his.

Your training for +-1 is limiting. What if its +2? Or heck what if you REALLY get held up? Or have to cut the dive super short? I contend that yes, you DO need more plans. You'll always have them and not have to scribble down stuff pre-dive and it makes planning 'what ifs' easier.

So what I do, is I have laminated tables with "18/45, 50%, 100%, depth ranges 140-190ft, bottom times 10-50mins" as an example. I typically have one 10ft depth segment per table, and they're double sided. So those 3 tables in my wetnotes cover anything I'm even remotely likely to get into when diving 18/45.

Say it turns out that your depth is shallower than you had planned. Its super easy to communicate the desire to extend the dive by referencing the tables DURING the dive.

Lost deco gas (imo) doesn't need a table as you do 1.5x the deco and share the gas with your buddy.

 

[Patoux01]

Or have to cut the dive super short? I contend that yes, you DO need more plans.

This one exactly.

 

[stuartv]

Okay, I see what you're saying now. But, since my buddy and I would each be diving with a computer as our primary, is the contingency for cutting a dive super short really that important to have written down? If one computer dies, protocol is to thumb the dive, right? And I'm not really talking about "exception" cases where you might do a dive without a computer or tables at all. I'm talking about when you're doing it however you view as being "right".

Also, dealing with the contingencies beyond the "planned' contingencies is:

a) why my instructor is going to teach us ratio deco, too.

b) why I'm asking about just diving 2 computers and not having any written plans at all. With a buddy, that's 4 computers. If I lose my buddy, well, I still have my 2 computers. The computer will do better at handling contingency planning than carrying tables, right? As long as it doesn't crap out. Which brings me back to my original question. And if the answer is not to rely solely on 2 computers because they could both crap out, well then how are you better off if 2 bottom timers crap out? Or is it viewed that it's plausible for 2 Petrels to crap out but not for 2 bottom timers to crap out?

 

[PfcAJ]

Imo, yes, having written plans that you can discuss and go over is important.

RD works well in a sweet spot of depths and times with certain gases. Outside of that it gets goofy.

Why do you think you need 4 computers? That's just excessive and I'd make a WAG that it stems more from not understanding the deco. See post #2 above.

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.

 

[stuartv]

Imo, yes, having written plans that you can discuss and go over is important.

Again, I repeat, I'm not talking about what you do pre-dive. I'm just asking about what you (would) take in the water with you.

RD works well in a sweet spot of depths and times with certain gases. Outside of that it gets goofy.

Why do you think you need 4 computers? That's just excessive and I'd make a WAG that it stems more from not understanding the deco. See post #2 above.

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?