Deco stop question

I don't know if I'll ask this correctly but here goes.

On programs like V-planner, what formula or bit of information tells the program to start deco stops at the depth it prints out?

In other words if I didn't have V-planner or GAP programs could I determine at what depth I should start deco stops?


I've had fun with the V-planner(thanks Lost Yooper) but I just don't understand how or why it comes up with the depths it comes up with.

Thanks for any enlightenment you can provide

Read how George explains the first stop and deep stops in the following. I could explain it, but its better if you read it directly.

http://www.wkpp.org/articles/Decompression/first_deep_stops.htm

and welcome to scubaboard.

from the link provided.

GI says to begin the deco stops at 80% of your profile in atmospheres. Why couldn't you just use the depth in feet or meters instead?

Can't answer the question, but just wanted to comment that conversion between ATA and feet/meters is a quick calculation and should be part of your basic arsenal of knowledge

conversion is simple. Just wondering why GI chooses to use atm when most people talk about diving to various depths in feet or meters. Given what he has accomplished I thought there might be a specific reason which I just couldn't figure out since the conversion is so simple and direct.

Originally posted by jbd
conversion is simple. Just wondering why GI chooses to use atm when most people talk about diving to various depths in feet or meters. Given what he has accomplished I thought there might be a specific reason which I just couldn't figure out since the conversion is so simple and direct.

Click to expand...

I obviously could not speak for GI, but my guess would be as follows:

Lets take a dive to 240ft.

240/33 + 1 = 8.27 ATA

8.27 ATA x 80% = 6.6 ATA

6.6 ATA = approx 185 feet.

Therefore the first deco stop would be at 185' (as I understand it)

Now, lets do the same dive except in feet instead of ATA's.

240 x 80% = 192

192' = approx 6.82 ATA

Is there a significant difference in my example between the actual ATA's and feet? No. Is the difference great enough to matter? Possibly. WKPP is doing things with decompression that no one thought possible. I certainly don't claim to understand all aspects of diving physiology and I can't say that the 7 feet in my example would make a huge difference or not. But at a different depth, that 7 feet could be the difference between a 6 ATA dive and a 7 ATA dive, and that *COULD* make a difference.

My point is that his formula seems to work, for whatever reason I don't understand. If I was to choose to use one, I would personally rather follow his proven method than try to devise an alternative one on my own.

But, for the moment, the decompression techniques they are using are beyond my skill level, and I will be doing a lot more learning and research before I attempt to use ANY of them.

Just my $.02.

Dive often, but dive safe

John

Originally posted by Cave Diver
I will be doing a lot more learning and research before I attempt to use ANY of them.

Click to expand...

AMEN to that!!!

great post. I think your logic is right on target. Let me add a wrinkle to the situation. From the 2nd paragraph of the linked article GI says," The best way to do this is to begin your decompression stops at 80% of your profile in atmospheres rounded up."

How does this, "....rounded up." come into play? Would it make up the 7' difference you came up with in your example?


I'll second TM's AMEN to that!!!

I'm just in the learning stages about decompression diving. Trying to figure out the theory and concepts before I try it.

I think I can answer the rounding up question.

From our open water experiences, when we use the PADI (or NAUI, or SSI, or whosever) dive planner, we are thought to always round up to the next deepest depth (if 51 feet, look at 60) or next highest time.

I've been taught that the same applies in tek diving.

Rounding upwards in diving typically gives you "that" much more of conservatism that you want to stay safe.

As an example, in my Advanced Nitrox/Deco Procedures class, I missed a question on the exam because I rounded down. One of my computed figures that I was to use to look up a value on a table came out to be 1.01 ATA (atmospheres). I did the mathematic convention and used the table figure based on 1.0 ATA.

But this was the "trick" within the exam question since even with that little bit of overage (.01), I needed to have rounded up to 1.1 ATA and use that table value.


Does that make sense?