Info Why are tables not taught in OW classes anymore?

[L13]

Trying to derive mathematically a profile having an issue, I instead found out that a multi-level dive with decreasing depth always leads to less load in all compartments than a dive of the same total time at the time weighted average depth (the proof is not hard, but probably out of scope for this thread).

Exactly!

 

[scubadada]

If the dives are fundamentally different, then you should be able to say whether a 15min dive to 30m is fundamentally an NDL dive or fundamentally a deco dive.

No, this is wrong. Despite many efforts to explain this, you persist. Decompression algorithms are models to help you avoid DCS on no stop dives and to effectively deal with the exposure and avoid DCS in decompression dives.

As a diver, you choose your computer, its decompression algorithm, and its settings. By doing so, you have chosen where to draw the line between no stop and decompression dives. Once you have made that choice, you should follow the guidance you are given by your computer.

If you later decide you have drawn the line in the wrong place, you may change your computer, the algorithm you use, and/or the settings. You then have a new line to distinguish between no stop and decompression dives.

I may think that you are ridiculously conservative for choosing a GF high of 60 for no stop dives, however, that is entirely your choice. You will surface from your example100 ft dive on air at about 8 min, I will have about twice that time. Both of had a nice no stop dive.

Hi
Should not all these pedantic explanations about English usage be removed from the basic forum?

Yes, this thread got way out of hand, again.

This thread is in the Basic Forum. Readers need to know that no stop dives do not exceed the NDL, they can make a direct ascent to the surface, and that a safety stop is recommended. If the NDL is exceeded, it is a decompression dive, they cannot make a direct ascent to the surface, and there is at least one mandatory stop required prior to surfacing.

I think most of us use these definitions

 

[dmaziuk]

Trying to derive mathematically a profile having an issue, I instead found out that a multi-level dive with decreasing depth always leads to less load in all compartments than a dive of the same total time at the time weighted average depth (the proof is not hard, but probably out of scope for this thread). That's probably what I was missing and the COMEX didn't when the established the table.

Are COMEX schedules derived from a strictly exponential model? -- Assuming the exponential model and the same starting Pinsp, I am not sure time T at depth D is exactly equivalent to T/2 at D*2: I think the latter should result in a slightly greater loading. But that aside, if you assume a linear-exponential model, your result may be very different, and I am not sure about sequential model either.

 

[boulderjohn]

If the dives are fundamentally different, then you should be able to say whether a 15min dive to 30m is fundamentally an NDL dive or fundamentally a deco dive.

I responded to this point as clearly as I could. I apologize for not making the point clear enough for you to understand.

 

[L13]

No, this is wrong. Despite many efforts to explain this, you persist. Decompression algorithms are models to help you avoid DCS on no stop dives and to effectively deal with the exposure and avoid DCS in decompression dives.

Are you contending that the dives are fundamentally different(NDL vs. Deco)? or that our behavior on the dives are fundamentally different?

I 100% agree with the latter, and strongly dispute the former. It is very possible we are talking past each other, and agree more than you think.

 

[L13]

I may think that you are ridiculously conservative for choosing a GF high of 60 for no stop dives...

I actually usually use 65%/85%. But I have used 50%/60% when diving with someone that wanted to be that conservative.

 

[scubadada]

Are you contending that the dives are fundamentally different(NDL vs. Deco)? or that our behavior on the dives are fundamentally different?

I 100% agree with the latter, and strongly dispute the former. It is very possible we are talking past each other, and agree more than you think.

Hi @L13

To be honest with you, I have not been able to follow your posts.

So, you tell me. You and I go diving and do a dive to 80 ft for 40 min on 32%. The only difference is that I dive 45/95 and you dive 35/75. I ascend with several minutes of NDL remaining, do a 3 min safety stop, and surface. You have exceeded your NDL of 28 min and have deco stops, 1 min at 20 ft and 5 min at 10 ft. You surface and join me on the boat. All calculations from Shearwater Teric NDL/Deco planners.

We did the same dive. My dive was a no stop dive, your dive was a decompression dive. We followed our dive computers and the settings we chose to use.

 

[inquis]

Are you contending that the dives are fundamentally different(NDL vs. Deco)? or that our behavior on the dives are fundamentally different?

The two are inextricably linked, so I find the question a bit odd. You cannot ignore the ascent portion of the dive, and that is obviously influenced by which side of the line it falls. And yes, I think people are talking past one another.

 

[L13]

Hi @L13

To be honest with you, I have not been able to follow your posts.

So, you tell me. You and I go diving and do a dive to 80 ft for 40 min on 32%. The only difference is that I dive 45/95 and you dive 35/75. I ascend with several minutes of NDL remaining, do a 3 min safety stop, and surface. You have exceeded your NDL of 28 min and have deco stops, 1 min at 20 ft and 5 min at 10 ft. You surface and join me on the boat. All calculations from Shearwater Teric NDL/Deco planners.

We did the same dive. My dive was a no stop dive, your dive was a decompression dive. We followed our dive computers and the settings we chose to use.

We did the same dive, at the moment we reach 20ft, we have experience identical compression and decompression. We have approximately the same nitrogen in or systems at that point. The rest of the dive were different, but not fundamentally different. As an NDL diver, you could have ascended directly to the surface, or done a 5 min safety stop. Each choice is not fundamental different in a physiological sense from my choice to spend 6min i the final stops. Each choice from your NDL choices to my choice are slight variations in chosen amount of risk to accept in our Surface GF.

Interestingly, I planed the same dive in Subsurface with 35/75 and it shows only a 3min deco stop at 10ft. Maybe the difference is ascent and decent rates.

But that kind of emphasizes my point. If we tweaked the dive parameters just right, we could get a dive with 45/95 that was NDL with a 3 min SS, but with 35/75 that was a "deco dive" with a 3min deco stop. I that case, fundamentally the dives would be identical. the only difference would be your perceived freedom to ascend directly to the surface at any time, and my perceived ceiling for the last 15-20min of the dive. The difference is in our perceptions, not the dive itself. Fundamentally, our risk from a direct ascent to the surface would be identical at any point in the dive.

 

[dmaziuk]

... fundamentally the dives would be identical. the only difference would be your perceived freedom to ascend directly to the surface at any time, and my perceived ceiling for the last 15-20min of the dive. The difference is in our perceptions, not the dive itself. Fundamentally, our risk from a direct ascent to the surface would be identical at any point in the dive.

And if you had completed your mandatory 3-minute deco stop, you'd get out of the water considerably more not bent than Craig with his 3-minute optional safety stop. That's how gradient factors work in a model whose outcome is incidence of clinical DCS.