How you write deco plan on your slate?

[lermontov]

Yeah, but now that I think of it, since I dive with two computers I'm not sure I really DO need a written deco plan. What you are describing is something different - I think that the discussion above was about a written ascent plan.

I guess a written plan with your turn pressure or maximum bottom time would be a helpful reminder for dive planning, but it's not really the same as a backup to your electronics.

yes its differant - was just indicating that the written notes are a complimentary tool and as you say a reminder - so mush easier than trying remember everything and eliminates brain fade when stressed

 

[doctormike]

written notes are a complimentary tool and as you say a reminder - so mush easier than trying remember everything and eliminates brain fade when stressed

^This.

 

[Nick_Radov]

Explanations exist; they have existed for all time; there is always a well-known solution to every human problem—neat, plausible, and wrong.
- H. L. Mencken

The deco algorithms backed by science and testing are not amenable to on-the-fly calculation.

Nah. If you actually read the scientific literature, there is very little direct scientific backing for most of what we do, and the error bars are huge. You can't point me to a single large-scale, real-world study that shows it's better to stop for 5 minutes at 50 ft and 6 minutes at 40 ft versus 6 minutes at 50 ft and 5 minutes at 40 ft (or whatever your preferred deco algorithm calls for). Much of current practice is extrapolated or empirical. Don't take it too seriously.

That said, you can get a rough approximation of the results of an actual deco algorithm using simple math, but only within specific parameters. Or, as stated in Ratio Deco – is it nonsense? – The Theoretical Diver

Sure, that's basically it. For a given deco algorithm and set of gasses, the relationship between depth, bottom time, and total deco time describes a complex 3-D surface. At any given point on that surface, you can place a tangent plane which provides an accurate approximation within reasonable limits. The trap that some divers fall into is a misguided focus on precision when what really matters is "good enough" accuracy.

The above examples demonstrate that it is possible to develop a approximation of a decompression model that provides a reasonable fit over a limited range of depths, bottom times and breathing gasses. Going beyond these limits the approximation starts to fall apart.

 

[Nick_Radov]

I'm not sure you understand the point of a written checklist.

The human brain is amazing, but it has failure modes. For example, if you are tired, hungry, angry, sick, or distracted. Or, in this particular example, when you have an unanticipated gear failure underwater.

But I guess that's impossible if you are absolutely sure that no matter what is going on, you will always be able to calculate deco in your head. I personally write a bailout plan on a slate. But hey... you do you.

Pilots use checklists, but they also have memory items for urgent procedures that they must know by heart and be able to reliably execute without referring to a written checklist.

Boeing 737 Memory Items – Engine Fire, Severe Damage or Separation

When something goes wrong while flying on the Boeing 737, we use the QRH (Quick Reference Handbook). We just have to find out the correct NNC (Non Normal Checklist) and then we just read it and exe…

www.johanpercherin.info

Adjusting deco plans on the fly falls into that category. While I am far from infallible and make many mistakes, this particular item is really simple. Divers who don't understand that or believe it's difficult were just not correctly trained in the first place. Fortunately, a competent instructor can teach this skill to any student capable of doing basic arithmetic within a few hours so it's an easy problem to fix.

A diver who is tired, hungry, angry, sick, or distracted should not get in the water in the first place. So, I don't know why you would bring that up? Exercise option 1 and come back another day when you're feeling better.

 

[doctormike]

Pilots use checklists, but they also have memory items for urgent procedures that they must know by heart and be able to reliably execute without referring to a written checklist.

Boeing 737 Memory Items – Engine Fire, Severe Damage or Separation

When something goes wrong while flying on the Boeing 737, we use the QRH (Quick Reference Handbook). We just have to find out the correct NNC (Non Normal Checklist) and then we just read it and exe…

www.johanpercherin.info

Adjusting deco plans on the fly falls into that category. While I am far from infallible and make many mistakes, this particular item is really simple. Divers who don't understand that or believe it's difficult were just not correctly trained in the first place. Fortunately, a competent instructor can teach this skill to any student capable of doing basic arithmetic within a few hours so it's an easy problem to fix.

A diver who is tired, hungry, angry, sick, or distracted should not get in the water in the first place. So, I don't know why you would bring that up? Exercise option 1 and come back another day when you're feeling better.

You know, you may be right.

 

[Wibble]

Nah. If you actually read the scientific literature, there is very little direct scientific backing for most of what we do, and the error bars are huge. You can't point me to a single large-scale, real-world study that shows it's better to stop for 5 minutes at 50 ft and 6 minutes at 40 ft versus 6 minutes at 50 ft and 5 minutes at 40 ft (or whatever your preferred deco algorithm calls for). Much of current practice is extrapolated or empirical. Don't take it too seriously.

Good point.

But... I've done hundreds of significant decompression dives following my preferred Buhlmann 50:80 algorithm and yet to be bent as a result. I therefore would not be a volunteer in the study to find the true normal distribution of bent/not bent.

If 50:80 keeps me in the water longer than I need, that's fine by me as the result -- not bent -- is highly desirable.

 

[Celt]

Diving on the fly is headless chicken diving, No plan and no discipline, and 100% will land you in trouble. Never do it shallow or deep. A plan demands discipline, if you like a DC or to write it down or both is up to the diver. Knowing the relationship between depth, time and decompression isn’t enough. I wouldn’t make a simple single tank dive without a plan.
Let’s all go off and make it up as we go along, no one knows what’s happening including the surface supervisor.

 

[lermontov]

here's is a paper that has looked at Ratio versus compartment models

https://www.dhmjournal.com/images/47/DHM-Vol47.1.pdf

page 9

 

[Wibble]

Diving on the fly is headless chicken diving, No plan and no discipline, and 100% will land you in trouble. Never do it shallow or deep. A plan demands discipline, if you like a DC or to write it down or both is up to the diver. Knowing the relationship between depth, time and decompression isn’t enough. I wouldn’t make a simple single tank dive without a plan.

We all agree with that.

However, what is "planning"? With experience, you know what the plan will be like; gases required, volumes required, bottom times, total runtimes, which catheter+undersuit+hood to use... Mainly because we've done it a load of times previously and have worked out how much gas is needed.

Nobody should dive "Alpinist" unless they've a plan which includes a Sherpa bringing the other gas they need.

The most important thing you learn on your basic deco course (ANDP - advanced nitrox and deco procedures) and further training such as normoxic trimix and MOD2... is how to plan the dive and all the nitty gritty detail that has to be considered in order for it to be a safe dive.

Let’s all go off and make it up as we go along, no one knows what’s happening including the surface supervisor.

Lost me at "surface supervisor"! The skipper's a taxi driver with no responsibility except being there to pick us up. Everything else is up to us to INDIVIDUALLY sort out.

If you don't have the requisite planning or diving skills; then it is only one person's fault and it's not the skipper or anybody else on the boat. Sorry, but I sat next to a person who didn't come back and I have an extremely hard view on self reliance.

 

[doctormike]

Lost me at "surface supervisor"! The skipper's a taxi driver with no responsibility except being there to pick us up. Everything else is up to us to INDIVIDUALLY sort out.

If you don't have the requisite planning or diving skills; then it is only one person's fault and it's not the skipper or anybody else on the boat. Sorry, but I sat next to a person who didn't come back and I have an extremely hard view on self reliance.

Off topic, but I do hear this a lot.

I'm not an attorney, but everything I have heard in the last decade or so suggests that the old "dive boat captain is just a taxi driver" concept is no longer a viable legal defense. Yes, divers have the responsibility for planning the dives, but the topside crew had obligations as well..