Ratio Deco

[decompression]

I'll post this here as its just good info for those that are unfamiliar with ratio deco.

https://m.youtube.com/watch?feature=youtu.be&v=tKSRs7NbQuM


Sent from my iPhone using Tapatalk

 

[tursiops]

That was remarkably uninformative. RD is a strategy. It took almost ten minutes to say that.

 

[decompression]

Tursiops.........you are already familiar with ratio deco......it's not an in depth, blow by blow discussion......it's a quick video blog.......but I get your point.


Sent from my iPhone using Tapatalk

 

[PfcAJ]

So according to AG you don't need to do a surface interval if you're using his magic ratio deco...gtfo

 

[WhiteSands]

So according to AG you don't need to do a surface interval if you're using his magic ratio deco...gtfo

In the 2 UTD classes I took, I was taught that if you did your min-deco stops, even on a dive to 20m for 30mins (on air), after a 1 hour surface interval you were essentially "clean". We were also told that because we were "clean" it was safe to fly, because we had already off-gassed in the water.

Using this logic, the instructor said that it was "safe" to do 4 dives to 30m for 20min each in one day (with a 1 hour SI in between) and you will be fine.

When I look up my PADI tables, if I did a 30m dive for 20mins on air, I will end up in pressure group "O" after 1 dive. After a 1 hour SI I will be in pressure group "E".

If I again went to do a second dive to 30m, according to the PADI tables, I will have only 10min max of NDL time. However, if I followed UTD's rules, I will end up going 10mins into deco.

Imagine if I repeated these dives a 3rd or 4th time after a 1 hour SI each, I will probably come very close to, or actually get bent.

Decompression, is what I was taught consistent with UTD doctrine, and what are your comments on this?

 

[decompression]

WhiteSands, the idea behind mindeco is to do a majority of your decompressing/off gassing in the water where you have more options. In the video, AG wonders a bit between ratio deco and min deco. So, yes, using the mindeco profiles with SIT either over or under 1 hour allows you to do multiple dives a day. Similar to PADI tables but with the benefit of making your off gassing as part of your dive.

Sent from my iPhone using Tapatalk

 

[WhiteSands]

Thank you Decompression. Yes that seems consistent to what I have been taught in my UTD classes.

I don't really know how much better (or that it is even better) Min-Deco is compared to doing safety stops at 3 mins at 5m. If we calculate total safety or "deco" stop time for min-deco (assuming a dive to 30m), 1min at 15m + 1min at 12m + 1min at 9m + 1min at 6m + 1min at 3m = total 5min of safety or "deco" stop time.

PADI and other recreational agencies teach divers to do a 3mins stop at 5m, so essentially min-deco has just 2min extra deco time compared to the traditional safety stop.

It seems a bit far-fetched to me that doing 2 min of extra safety stop time will magically make you "clean" whereas if we follow the NOAA (PADI) tables we end up in pressure group "O", with a lot of residual Nitrogen in our bloodstream.

Plus at the back of my mind, I am thinking of the NEDU study which basically says if you have to choose where to do your stops given a limited amount of time, it's probably better to do it shallow. This, suggests to me, that perhaps the recreation style safety stop of 3min at 5min might result in better off-gassing then min-deco.

But putting that aside, it seems pretty far fetched, even if we do assume doing the "deep" stops has some marginal benefit, that it will make you clean after 1 hour of SI, don't you think?

 

[Adobo]

If we calculate total safety or "deco" stop time for min-deco (assuming a dive to 30m), 1min at 15m + 1min at 9m + 1min at 6m + 1min at 3m = total 4min of safety or "deco" stop time.

PADI and other recreational agencies teach divers to do a 3mins stop at 5m, so essentially min-deco has just 1min extra deco time compared to the traditional safety stop.

You guys wouldn't do a stop at 12m on that dive?

 

[WhiteSands]

You guys wouldn't do a stop at 12m on that dive?

My mistake. Added a stop at 12m. Will edit previous post.

If I may add on to some other stuff I was taught/told that left me scratching my head. We were repeatedly told that UTD does not rely on models, tables, computers etc. and the idea was that these were somehow inferior to ratio deco. UTD uses it's version of ratio deco exclusively for dive planning.

From what I understand, isn't ratio deco just a handy approximation or heuristic for what a particular model generates so that you can easily make changes to your dive plan on-the-fly (within reasonable limits)? But if you go outside the window where ratio deco works, then obviously ratio deco starts to fall apart. It then seems strange to me to bash the decompression model, when ratio deco itself is a method of approximation that tries to mimic the underlying model from which it was derived.

I could never then understand how ratio deco could be used as a stand-alone model to calculate decompression, since it is just a heuristic for some other model, and only works within certain parameters.

Or have I horribly misunderstood all this?

 

[PfcAJ]

In the 2 UTD classes I took, I was taught that if you did your min-deco stops, even on a dive to 20m for 30mins (on air), after a 1 hour surface interval you were essentially "clean". We were also told that because we were "clean" it was safe to fly, because we had already off-gassed in the water.

The stuff UTD is peddling is make-pretend. You can see it for your self when looking at the PADI dive tables. Capital baloney, and its apt to get someone hurt.

Don't get me goin' on his 'ratio deco' for proper deco dives. Absolutely preposterous.

Using a simple set of rules to come up with an ascent schedule that's close or the same to an established algorithm is one thing. Ignoring the algorithm and suggesting that the ratio is the 'gold standard' is beyond the pale.