Dir Divers!!!

[Bowers]

I have a UTD buddy who still dives with only a bottom timer. I like to use ratio diving as a sanity check or backup to my computer but he uses it as the primary method. For recreational dives he always uses 32% and then simply does the 130-depth=NDL. Other things that make this work are slow ascents. You ascend at 30ft/min nearly halfway then stop for a minute, then continue ascending at 10ft/min, to safety stop before surfacing. When doing slow ascents like this you optimize off gassing and therefore with a 1 hour surface interval are safe to do it again without modification.
Tec diving ratio deco is more complicated but similar principles and was my primary method for my first 50 or so dives until I purchased a proper Tec computer. It kept me perfectly safe but usually do to built in conservancies ended up requiring longer deco stops than necessary (which I preferred over wondering if I was pushing the ticket).

Disclaimer- I am not a ratio instructor and did not cover other nuances so don't try this without proper training...

 

[JoeTPhilly]

I have a UTD buddy who still dives with only a bottom timer. I like to use ratio diving as a sanity check or backup to my computer but he uses it as the primary method. For recreational dives he always uses 32% and then simply does the 130-depth=NDL. Other things that make this work are slow ascents. You ascend at 30ft/min nearly halfway then stop for a minute, then continue ascending at 10ft/min, to safety stop before surfacing. When doing slow ascents like this you optimize off gassing and therefore with a 1 hour surface interval are safe to do it again without modification.
Tec diving ratio deco is more complicated but similar principles and was my primary method for my first 50 or so dives until I purchased a proper Tec computer. It kept me perfectly safe but usually do to built in conservancies ended up requiring longer deco stops than necessary (which I preferred over wondering if I was pushing the ticket).

Disclaimer- I am not a ratio instructor and did not cover other nuances so don't try this without proper training...

After a surface interval of 1-2 hours the Practical MDL is 50% and 2 hours or more it is 75% of the calculation.

 

[boulderjohn]

You ascend at 30ft/min nearly halfway then stop for a minute, then continue ascending at 10ft/min, to safety stop before surfacing. When doing slow ascents like this you optimize off gassing and therefore with a 1 hour surface interval are safe to do it again without modification.

Could you please show a link to the research that supports this?

 

[boulderjohn]

I am goin

You ascend at 30ft/min nearly halfway then stop for a minute, then continue ascending at 10ft/min, to safety stop before surfacing. When doing slow ascents like this you optimize off gassing and therefore with a 1 hour surface interval are safe to do it again without modification.

After making the previous post I figured I would cut to the chase. There is no research supporting this claim about the benefits of this ascent process, and the people who created the process do not claim that there is.

A few years ago I wrote an article on current thinking on ascent profiles for decompression dives, and I was greatly assisted by Dr. Simon Mitchell. When I was done, I wanted to write an article on thinking on NDL ascents, and I asked his help. He graciously refused, saying there is not enough good research on different ascent profiles on NDL dives to form an opinion. I set out to do research on my own, and I eventually realized he was right.

As part of my research, I contacted GUE headquarters and asked for the thinking behind the min deco ascent profile. I got a thorough explanation. The primary thinking behind that ascent profile is that the shallower portion of the ascent should be slower than the deeper portion. They choose the halfway point of the ascent to make the change because they figure anyone has the ability compute a half. Doing it in 10 foot segments guarantees that the shallower portion will be slower, and it has the benefit of being consistent with the way they ascend on decompression dives.

That's it. There is no belief that doing that kind of an ascent rather than another ascent profile shortens the surface interval. There is no research supporting the process.

 

[lowwall]

Could you please show a link to the research that supports this?

 

[crofrog]

I have a UTD buddy who still dives with only a bottom timer. I like to use ratio diving as a sanity check or backup to my computer but he uses it as the primary method. For recreational dives he always uses 32% and then simply does the 130-depth=NDL. Other things that make this work are slow ascents. You ascend at 30ft/min nearly halfway then stop for a minute, then continue ascending at 10ft/min, to safety stop before surfacing. When doing slow ascents like this you optimize off gassing and therefore with a 1 hour surface interval are safe to do it again without modification.
Tec diving ratio deco is more complicated but similar principles and was my primary method for my first 50 or so dives until I purchased a proper Tec computer. It kept me perfectly safe but usually do to built in conservancies ended up requiring longer deco stops than necessary (which I preferred over wondering if I was pushing the ticket).

Disclaimer- I am not a ratio instructor and did not cover other nuances so don't try this without proper training...

That's now how those profiles work.

If you run the same bottom time 1hr later you're surfGF is going to be ~97%, versus roughly 85% for dive 1.

 

[Bowers]

Could you please show a link to the research that supports this?

I am goin

After making the previous post I figured I would cut to the chase. There is no research supporting this claim about the benefits of this ascent process, and the people who created the process do not claim that there is.

A few years ago I wrote an article on current thinking on ascent profiles for decompression dives, and I was greatly assisted by Dr. Simon Mitchell. When I was done, I wanted to write an article on thinking on NDL ascents, and I asked his help. He graciously refused, saying there is not enough good research on different ascent profiles on NDL dives to form an opinion. I set out to do research on my own, and I eventually realized he was right.

As part of my research, I contacted GUE headquarters and asked for the thinking behind the min deco ascent profile. I got a thorough explanation. The primary thinking behind that ascent profile is that the shallower portion of the ascent should be slower than the deeper portion. They choose the halfway point of the ascent to make the change because they figure anyone has the ability compute a half. Doing it in 10 foot segments guarantees that the shallower portion will be slower, and it has the benefit of being consistent with the way they ascend on decompression dives.

That's it. There is no belief that doing that kind of an ascent rather than another ascent profile shortens the surface interval. There is no research supporting the process.

I don't argue with this at all. I don't know of any research on it. But this is what my buddy does for recreational dives (I'm not being coy, it really is a buddy who does it, not me).
I have however used ratio deco in technical diving and been fine for repetitive dives. However my technical dive ratio profile is done with a built in conservancy that generally had me on 100% for several minutes longer than my buddies who were on computers.

 

[boulderjohn]

I don't argue with this at all. I don't know of any research on it. But this is what my buddy does for recreational dives (I'm not being coy, it really is a buddy who does it, not me).

If you really look at what little research there is available, you will see that it is hard to make any comparisons of any typical ascent profiles typically in use. Just as there is no research to show that the ascent profile is superior, there isn't anything to clearly show it is worse. As yourself how different it is from the ascent profile used by probably more than 90% of NDL divers--ascend at 30 FPM and do a 3-5 minute safety stop.

Let's say 3 people go on a dive at the same time. Each one dives to 100 feet. Diver A stays at 100 feet for 18 minutes and begins a 30 FPM ascent and finishes the ascent with a 5 minute safety stop. Diver B does the ascent profile you have described. Diver C stays at 100 feet for 15 minutes, goes to 80 feet for 7 minutes, goes to 50 feet for 20 minutes, goes to 30 feet for 30 minutes, and finishes with a 3 minute safety stop. I would expect all three to be just fine at the end of the dive.

That is what makes NDL dives different from what we commonly call decompression dives. Research has shown a significant difference in ascent profiles. In one case, the UTD Ratio Deco profile was compared to a Buhlmann profile that would not be considered the best today, and it clearly did not have a good outcome (look up the Spisni study).

 

[rjack321]

I have a UTD buddy who still dives with only a bottom timer. I like to use ratio diving as a sanity check or backup to my computer but he uses it as the primary method. For recreational dives he always uses 32% and then simply does the 130-depth=NDL. Other things that make this work are slow ascents. You ascend at 30ft/min nearly halfway then stop for a minute, then continue ascending at 10ft/min, to safety stop before surfacing. When doing slow ascents like this you optimize off gassing and therefore with a 1 hour surface interval are safe to do it again without modification.
Tec diving ratio deco is more complicated but similar principles and was my primary method for my first 50 or so dives until I purchased a proper Tec computer. It kept me perfectly safe but usually do to built in conservancies ended up requiring longer deco stops than necessary (which I preferred over wondering if I was pushing the ticket).

Disclaimer- I am not a ratio instructor and did not cover other nuances so don't try this without proper training...

This is more of less what people actually do yes. I'm not convinced the ascents make anything "better" however