UTD Decompression profile study results published

[elmo]

Will a Shearwater not tell you the same ?

As well that is a abnormal or ill diving behavior to change your dive plan, how did that impact the gas calculated? or was that 1st wreck not intended for a Deco dive anyway

I think my Shearwater is great but I don't know how to make it tell me what my deco obligation will be if I move up to 130' and spend the next 15min there. But if you are familiar with how change in depth and bottom time affects your profile you can do it.
As you pointed out, you need to consider gas planning too. But if you know that every 5 min you breath 15-20 bar (I think that's ~225-300 psi) from your twin 12 (100cuft) double, and know what your minimum gas is at 130', you can look at your gauge and say if I go up 20', I can increase my bottom time by 5min and my deco obligation will be similar. Your team needs to have a similar philosophy.
That is NOT to say you needed to come up with your original plan with whoever's version of ratio deco. You could plan it with any sensible gradient factors you like. You just need to know how to adjust your plan if needed/desired. You do need to understand what the significance is of changes in depth and bottom time to deco and gas consumption. I call that ratio deco, but I'm happy if you call it something else.
(I don't think this is quite the UTD position btw but I've never taken their training)

 

[Tassi Devil Diver]

I'll give you a real life example of a dive I did where ratio deco was super helpful.

Primarily diving a rebreather, for the dive you describe, me and my buddy would have planned our dive on a time to surface of say 1hr, and used our dive computers to dictate the revised bottom as depth changes

Many of the dives I do are multi level with an expected maximum depth but the actual dive profile is uncertain and always use dive computers in this way and find it rather effective, especially as most serious tek divers seem to have two decompression computers. Can't see that ratio deco is of any advantage in this situation (or any situation).

 

[ajduplessis]

Could some one explain to me what is the point of ratio deco!!

This is my view on RD and only an opinion. Use, don't use.

Ratio Deco is for those divers that don't want to plan and calculate profiles for different scenarios before entering the water. If this was not the case, why not plan and verify possibilities before entering the water???? Why do goals and dive objectives change during "planned" dives, especially where decompression is required? What happened to "dive your plan"?

Make no mistake, Ratio Deco is usable tool and dived successfully by many diver without problems. However, tools are sometimes used incorrectly, not understanding the limitations and this creates a slippery slope.

Here are some good examples of mistakes made when making changes on the fly utilising RD.

 

[TrimixToo]

My (very rudimentary) knowledge of RD is a valuable backup tool to me. If my computers decide to disagree, it can help me surface unharmed by choosing the right one to follow. I have had computer malfunctions underwater, and once, before I had two computers that knew what I was breathing, an unexpected low battery warning on the one that did know. It was very comforting to calculate the stops in my head and see that computer was doing things at least approximately right.

On that basis alone, I think it should be taught. But I'm going to keep using my computers to guide my ascents when I have no reason to suspect them.

 

[rossh]

Could some one explain to me what is the point of ratio deco!! I cant see how it can optimize deco or any "benefits to the methodology of Ratio Deco that transcend any single decompression schedule".

Yes I see there are patterns in decompression like for every minute I spend at 40m equates to minute of decompression or for every 1 minute at 70m equates to 3 minutes of deco. But a computer will do a far better job at optimizing deco based on actual depth changes and variations in ascent rate, and as for using ratio deco as a back up I carry two trimix dive computers, heck I could even carry a third with me.

I just don't see the point of any agency persisting with ratio deco, other than as some sort of gimmick to set them apart from other training agencies.

Go back 15 years - no iPhones or Androids, or other wide spread handheld computer. The few available tech dive computers back then that planned in GF or VPM were rare and expensive, or non-existent. Instead you cooked up a paper plan at home on the PC, and brought that with you and transferred onto a slate.

So RD was very useful to be able to adjust a plan or have the boat go somewhere else and invent a new plan. RD and that simplistic planning concept was most useful.

But today, everyone has a tech planning tool on their phone, and probably a dive computer that does the same too. Perhaps the evolution of small hand held computing, has sort of made simple RD style formula a little unnecessary.

.

 

[PfcAJ]

Will a Shearwater not tell you the same ?

As well that is a abnormal or ill diving behavior to change your dive plan, how did that impact the gas calculated? or was that 1st wreck not intended for a Deco dive anyway

No a shearwater will not tell you the same. It only tellsvyou your current deco obligation, not what your deco will be if you move 20ft shallower and stay for 10 more minutes.

It's all about flexibility. I *can* dive a rigid plan, but I also can adjust the plan in the water because I have the tools to do so.

Gas impact is pretty simple. If you know min gas and how much you're using say per 5min increments you can look at your gauge and see if you have enough. In any case you're either limited by Deco time (often how much deco gas you're carrying or how much deco you're willing to incur given the conditions) or minimum gas.

Tools in your toolbox.

 

[AlexL]

It is possible for computers to make errors or quit working.

isn’t there an easy solution to this problem? carry a backup. if both your computers, and all of your team's computers fail, maybe you should not have kicked Murphy's dog on the way to the dive site.

 

[Tassi Devil Diver]

No a shearwater will not tell you the same. It only tellsvyou your current deco obligation, not what your deco will be if you move 20ft shallower and stay for 10 more minutes.

It will tell you on the fly as you change depth, moving shallower you are going to get more bottom time, no need for any RD voodoo.

 

[PfcAJ]

It will tell you on the fly as you change depth, moving shallower you are going to get more bottom time, no need for any RD voodoo.

You have to do it to see it. The delta 5 and plus 5 functions only work for the depth you're at. It's not predictive.

It's really not voodoo.

 

[boulderjohn]

isn’t there an easy solution to this problem? carry a backup. if both your computers, and all of your team's computers fail, maybe you should not have kicked Murphy's dog on the way to the dive site.

I carry two computers myself--I was just explaining how things were taught to me.