Modified ratio deco

[LFMarm]

I heard that Patrick Widmann uses a modified version of ratio deco that is very accurate. Does anybody know what it is?

 

[rjack321]

I heard that Patrick Widmann uses a modified version of ratio deco that is very accurate. Does anybody know what it is?

I don't know what you consider accurate, but I would highly recommend you find better sources to trust.

 

[LFMarm]

I don't know what you consider accurate, but I would highly recommend you find better sources to trust.

I heard this in an interview. My source is the Shearwater Petrel but like to have a way to predict TTS increase for deviating dive plans.

 

[inquis]

but like to have a way to predict TTS increase for deviating dive plans.

Is the ∆+5 not enough info?

 

[LFMarm]

Is the ∆+5 not enough info?

For sure. But you can only see the current, not what ifs (how does TTS change if I stay for x minutes at this other depth?).

 

[InWay2Deep]

Achim on ISE YT channel has been talking about this deco methodology for deep diving recently and how he's not using (following?) a computer, my guess is he's doing ratio. I haven't followed super close but there might be some more details in his videos.

 

[inquis]

how does TTS change if I stay for x minutes at this other depth?

I believe you can run the deco planner during a dive. Not having done it, though, I don't know if it bypasses the depth/time entry.

 

[tbone1004]

I heard that Patrick Widmann uses a modified version of ratio deco that is very accurate. Does anybody know what it is?

This is going to sound harsh, but you need to plan your dive and dive your plan.

Ratio Deco is at best extremely risky and goes against everything we understand about decompression theory. All of the BS about you know your body is just that, BS, you can't do decompression by feel. You need to learn how you feel after dives to learn how to adjust your personal gradient factors, sure, but you aren't just going to say "ya know what, this part of my body doesn't feel great so I should probably spend some more time at this depth", that's nonsense. You can't do math better than a computer, the computers are reliable, and unlike when Ratio Deco was getting popular, the computers can actually handle the dive profiles we are doing now so there is 0 benefit to try and do better than your computer, and you will ALWAYS lose, so don't bother trying. Ratio Deco stems from people seeing trends in decompression plans created by software and they figured out that some things were "close enough" that it wasn't worth printing out new tables for every dive and the computers of the time couldn't handle what they were doing or were prohibitively expensive, unfortunately this was made obsolete about 15 years ago. No longer are bottom timers 1/4 of the price of a full deco computer, no longer are computers coming with only "generic" safety factors that they refuse to tell you, they're running the same algorithms as the deco software used to create the tables and are running it in real time for the same price as the bottom timers. Certain agencies haven't adapted with the times and are perpetuating this nonsense.

Now, the productive part. Start playing with decompression software, that's how these "magic ratios" were compiled in the first place. They would sit for hours with Deco Planner or similar and print out tables and eventually they got sick of having to print out new tables for everything. The arguments you still hear from guys like The Great Dive Podcast that still use Ratio Deco are not invalid though, you NEED to have a general idea of what your ascent profile is going to look like at any given time. You don't necessarily need to know down to the minute on each stop depth, but you should be expecting a general amount of time before you look at your computer. I.e. I think the TTS should be 60mins and it's 54mins or 63mins, that's close enough. What you shouldn't be doing is getting surprised when you look down and think you have 20 and then it's 54. That is their argument for teaching Ratio Deco is that people are blindly following their computers, though I would argue it's that they aren't properly planning their dives before hand.

To your comment about wanting to know what happens if you stay for +5 at a different depth, that's the kind of thing that you should be knowing before you even get in the water. What is your planned depth and bottom time, what is your +5 and +10 at that depth, what is your +10ft/3m for bottom time and +5 and +10 at that depth. This all depends too on what kind of diving your doing. If you're shipwreck diving it's easy, set a worst case dive plan for your best SAC rate at the sand and you know it's not going to exceed that. Reality is going to be your normal SAC rate at the deck height.
The only time this gets weird is when exploring virgin cave on CCR, which I presume you are not doing, but is what Patrick is doing. When you're doing that you have an exit radius that you have to stay within from the door and you don't actually know what the depth profile is going to look like and that's where you set some multi profile dives into deco planner. You can set the part of the profile you know, then add a section that says "I'm going to plan for an extra 20mins at the same depth, and an extra 20mins at +10ft and +20ft" and then put the exit profile, then you know the general look.

The ratios only work for certain very specific profiles, especially when on CCR, so what he is doing is only applicable to the types of diving that he is doing and does not apply outside of those very specific environments. It's one thing if you're doing generally static type dive profiles where you can figure those ratios out. If I'm on OC, I only need to take a watch into the majority of Florida caves, I know the depth profile and I know the general ratios for decompression on each of the general depth profiles of those caves, but that doesn't apply to me outside of that environment and it only comes with experience. You are looking for an extremely dangerous shortcut to proper dive planning, I would urge you to reconsider.

Easy example that took <5mins in Deco Planner. I know it takes me 30mins at an average depth of 80ft to get to the end of the line and the last deco time was 6mins. I'm going to explore for another 20mins, then come back. Deco time is 15mins. I know that exact numbers will vary on the dive but generally expecting 15mins.

I did see on my last tie-off though that it was looking like it heads down, so what should it look like if we go down to 100ft average, 21mins expected deco.

I'm on OC EAN32 which has a MOD of 100ft, but on the offchance it does drop a few feet down I'm willing to accept the slightly higher ppO2 and gas density, so worst case if it goes to 110 then I have a 25min deco obligation.

So what I know is that if I stayed on the shallower side and had a total run time between 60-100mins then I should have between 5-15mins of deco and if I was at the 100mins and on the deeper side then it should be between 15-25mins of deco. I can see that with the avg depth and time before I start the ascent and it will pass the sniff test. I don't need to be doing mental math while transiting a cave. It's a different thing if you're doing open water diving and have nothing better to do while on a vertical ascent, but in a cave you are often traveling and on big dives, often on a DPV so that is not the time to be crunching numbers. You set the lane lines, make sure the computer is giving you something within those boundaries, and let it ride.

This gets a bit weird on CCR at trimix depths, but since you have to plan your exit and ascent assuming you're on OC, I just plan the dive as if I was on OC the whole time and know that with the CCR I should be trending a bit shorter. I'll usually play with the bottom gases a bit to get the ppO2 at my expected setpoint, but I leave the deco gases alone.

 

[LFMarm]

Great explanation. Thank you! I am definitely not doing cave exploration.