UTD Decompression profile study results published

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If you do so as you described, staying longer and deeper, then you are eating you gas planned and entering in your contingency gas quantity ( or extra gas in case of Shait hits the fan )

So yes you know you can stay a little longer and a bit deeper because you have that extra gas available that we all put in our planning, so you are getting very tight in that extra gas and you leave less room for when Shait hits the van, it seems to me very loosely taken planning of initial planning modification, the likelihood of shait hitting the van is small but it is there, and it can bight your ars

And as Stuard mention you put in you planning a depth cap that you are actually not diving as a contingency, so you always fulfill your dive plan, but if you go beyond that, you are just playing with murphy's law.

We in no way, shape, or form are into our contingency gas, as we dive to minimum gas rules. Minimum gas is unbreakable. That is gas that does not get factored into your dive plan. If as a team, you decide 100 bar is minimum gas for that dive, and you all have a 220 bar fill, you have 120 bar to use on that dive. Guess what happens if you hit minimum gas 25 minutes into a 30 minute planned bottom time? It's time to head home. You lose 5 minutes of your planned dive. None of us had even come close to minimum gas on the day we extended our dive. We checked gas pressures before we made the decision to continue our dive, and by the time we started our ascent, the person with the lowest amount of gas still had 20 bar more than what our minimum gas reserve was. The point is, we knew we had enough gas to continue, even if something went wrong. Conditions aren't always great in the UK, and when the water is warm and you have 15m+ of vis, if you have the gas and time to extend your dive, you bloody well do it.
 
if I stay at this depth for 20 more minutes it will tack on 60 more minutes of decompression". Actual numbers.

Why can't you use the Shearwater @+5 to figure out the same thing?
 
Could some one explain to me what is the point of ratio deco

Hello Tassi,

Thanks for the question. My personal view on it may not benefit the next diver, and it stands on my own accord entirely, so please take this just as one personal view.

Ratio Deco builds on standard gasses.
If one doesn't know what specific depth one is going to, I can use the that framework to prepare for a sequence of dives in the exploration domain, which would in some cases make an "optimal" gas and deco approach difficult (how do you mix the "perfect" gas for a dive that you don't know the depth of yet?), but rather build the dives on gas logistics, Ratio Deco and maximal operative depth, in a manner proactive rather than reactive in-water.
Further, it works well in a mixed team, across rebreathers/open cirquit systems as well as any number of personnel.

Personally, if I travel to a different country or continent, and meet a person I want to go diving with, and we don't speak any of the same languages, which happens, that's samlessly facilitated as well, in terms of decompression. There's no way to quantify such utility with doppler technology.

To be sure, Ratio Deco doesn't numerically factor in, say, fatigue, hydration, exertion, temperature, nor do the alternatives, to my knowledge. But it does certainly build a familiarity and readiness towards adaptation, which may or may not be helpful in some circumstances.

In the classroom, I see the educational benefits in progressive addition of further "layers" when using the Ratio Deco-methodology as quite significant. As an open water diver, one learns the base upon which technical dives build it's approach, and so, as a diver, I attain recognition across levels of education and familiarity in application to diving.
Viewed separately as a training tool, I find it beneficial to add the deco sphere of Ratio Deco to the awareness of a diver, that they naturally learn to manage not just the dive as it may unfold, but at the same time consider and evaluate deco versus gas logistics and make choices based upon those factors.

These benefits of course wouldn't be quantified in a comparative study, which is why I think they're benefits that transcend how two deco plans for one dive work, compared to oneanother.

There's of course the cost factor, which naturally shouldn't dictate our choices, but in fairness, my 330 has cost me less than $1 per month in use towards computer and software, training cost aside (I omit that cost as I assume it would be a factor near enough constant across solutions/agencies, and even if it isn't, Ratio Deco surely wouldn't be the only factor differing across them).
Further, I don't depend on external hardware or software, and I don't risk taking on a habit of "outsourcing" my thinking.

These factors may not apply similarly or be weighed equally by all, and it's fair enough to point that out.
I am merely explaining examples of what I mean by benefits that transcend comparison of an "optimal" deco or gas for one dive versus a "standard" deco or gas for that same dive, specifically.

I hope my expansion brings clarity to my statement quoted, if not, I will be happy to take any questions you might have.


Best Regards,

Dan
 
Ratio Deco builds on standard gasses.
If one doesn't know what specific depth one is going to, I can use the that framework to prepare for a sequence of dives in the exploration domain, which would in some cases make an "optimal" gas and deco approach difficult (how do you mix the "perfect" gas for a dive that you don't know the depth of yet?), but rather build the dives on gas logistics, Ratio Deco and maximal operative depth, in a manner proactive rather than reactive in-water.

Don't you select your Standard Gases based on a target depth, where there is a list of depth ranges? So, you choose your SG based on the depth you are planning to dive to, by consulting a table of gases?

How is that better? You have, say, 5 gases to choose from for all possible depths. With a Best Mix approach, you have a huge number of gases to choose from, including all the same mixes that are in your list of SG. Let's say (hypothetically) that you have a standard gas for the range of 30m(100fsw) to 45m(150fsw). And a different gas for the range of 45m(150fsw) to 60m(200fsw).

Now suppose you're going to do a dive and you're not sure what the bottom will be, but you are pretty sure it's around 45m +/- 5m. With SG, you have to either choose a gas that is so rich that you could end up not being able to go as deep as you want, OR you have to choose a gas that is very lean and results in excessive deco. With a Best Mix approach, you could select a gas that would be just right for 50m - so you could be assured of going as deep as you might want, but it is not so lean that if you end up only going to 40m, the gas results in unduly long deco.

When you are planning where you don't know a specific depth, it seems like the Best Mix approach is significantly better than the Standard Gas approach. After all, if you plan using Best Mix, you CAN still choose the same mix as you would in a Standard Gas approach - if it really is the best mix for the dive you're planning. But, you are also free to choose something else if it would be better for your particular scenario.

I haven't had the formal training on SG and RD, but to an outsider, it SEEMS like the only real justification for standard gases is that you have learned to plan your dive using RD and RD depends on them. I.e. the tool you are using forces you to accept limitations on the gases you can use. All the other "reasons" I've ever seen or heard just seem to be rationalizations piled on top of that.

Ease of blending? Hey, if you're in a situation where ease of blending makes a certain gas preferable, the Best Mix approach will totally accommodate you choosing your gas based on that - it just wont' require you to choose that gas. Personally, I have never done a dive where that made one ounce of difference. When the gas I want isn't what is banked at the fill station I'm at, I request a custom blend and it doesn't make it any harder or more expensive for me whether I choose a custom blend that is a standard gas or a custom blend that is my own requested concoction. However, I can see where it could be a valid concern if you're taking some big bottles, a whip, and doing your own fills on site. Then, like I said, you can choose to use a mix that is the same as a standard gas if you want to. So, Best Mix doesn't have any disadvantage there.

Personally, if I travel to a different country or continent, and meet a person I want to go diving with, and we don't speak any of the same languages, which happens, that's seamlessly facilitated as well, in terms of decompression. There's no way to quantify such utility with doppler technology.

Huh? "no way to quantify such utility with doppler technology" What does that even mean?

As far as traveling to a different country and diving with someone that speaks a different language, how is RD better, or even as good as, agreeing on using Buhlmann and the same Gradient Factors? I could speak exactly zero of another diver's language, but I could show them my Perdix, what algorithm it's set for, the GF it's set for, and they could show me theirs matches, and we could dive without having to converse at all.

People are fond of saying RD is not an algorithm, it's a strategy. So, which sounds easier to you - planning a dive with someone who doesn't speak your language where you have agreed on a deco strategy? Or planning a dive with someone who doesn't speak your language where you have actually agreed on a specific algorithm and parameters?

To be sure, Ratio Deco doesn't numerically factor in, say, fatigue, hydration, exertion, temperature, nor do the alternatives, to my knowledge. But it does certainly build a familiarity and readiness towards adaptation, which may or may not be helpful in some circumstances.

RD is unique in that? Diving using Buhlmann and GF somehow precludes the diver from building familiarity with their personal deco and what they may choose to do when they are fatigued or feel less well-hydrated, or whatever?

I feel like having a measured, repeatable, accurate and precise baseline to work from is better than an on-the-fly mental calculation. My computer will give me a different baseline to use my judgment against if I dive to 90' for 15 mins, then go to 130' for 15 mins, versus if I start at 130' for 15 mins then go to 90' for 15 mins. Either of which I would rather work from, as a baseline, than starting with the info that I have been down for 30 mins and my average depth is 110'.

There's of course the cost factor, which naturally shouldn't dictate our choices, but in fairness, my 330 has cost me less than $1 per month in use towards computer and software, training cost aside (I omit that cost as I assume it would be a factor near enough constant across solutions/agencies, and even if it isn't, Ratio Deco surely wouldn't be the only factor differing across them).

Cost? You choose to use a deco method that seems to be quite clearly one that produces longer, slower ascents than commonly accepted modern, computer-based ascents produce. How much extra helium are you using and how do you factor that into your cost analysis?

Further, I don't depend on external hardware

You don't use a depth gauge? Perhaps you meant that you only use mechanical depth gauges and mechanical timing devices? Because if you are using an electronic device to tell you your depth, your time, and maybe even your average depth, then your statement may possibly be a Kool-Aid-induced hallucination?

When you talk about your "330", do you mean a Uwatec/ScubaPro bottom timer? They don't give those things away. When you factor in the extra cost of the gas required for the longer, slower ascents you get from RD, how long do you really think it would take to have saved enough to pay for the difference in price to a proper tech computer?

And, are you using the 330 to tell you your average depth, or are you tracking it in your head (but still assuming that the 330 is accurate on your depth and run time)?
 
Don't you select your Standard Gases based on a target depth, where there is a list of depth ranges? So, you choose your SG based on the depth you are planning to dive to, by consulting a table of gases?

How is that better? You have, say, 5 gases to choose from for all possible depths. With a Best Mix approach, you have a huge number of gases to choose from, including all the same mixes that are in your list of SG. Let's say (hypothetically) that you have a standard gas for the range of 30m(100fsw) to 45m(150fsw). And a different gas for the range of 45m(150fsw) to 60m(200fsw).

Now suppose you're going to do a dive and you're not sure what the bottom will be, but you are pretty sure it's around 45m +/- 5m. With SG, you have to either choose a gas that is so rich that you could end up not being able to go as deep as you want, OR you have to choose a gas that is very lean and results in excessive deco. With a Best Mix approach, you could select a gas that would be just right for 50m - so you could be assured of going as deep as you might want, but it is not so lean that if you end up only going to 40m, the gas results in unduly long deco.

You need to run a deco plan and conspire the differences between 21/35 and 18/45 for that proposed dive.

Hint: it's like 5mins. Hardly "unduly long".

You also need to compare the po2 for max depth using those gases. There a lot of built in flexibility.

My computer will give me a different baseline to use my judgment against if I dive to 90' for 15 mins, then go to 130' for 15 mins, versus if I start at 130' for 15 mins then go to 90' for 15 mins. Either of which I would rather work from, as a baseline, than starting with the info that I have been down for 30 mins and my average depth is 110'.

We literally went through this exact same exercise a few months ago and determined the deco difference to be 1 minute. A single minute.

You're supposin' what the deco difference is instead of actually putting them into planning software and looking for yourself.
 
Best mix is awesome on paper. Not so much after your sites change or you get blown out and the best mix in your tanks isn't the best anymore.
 
I've run it before, but I just did again, just for you.

For 130->90 (on air, GF50/80), I get 70 minute run time.

For 90->130, I get 77 minute runtime.

Since I would use best mix, I ran it again for a more realistic bottom time and gas.

EAN28, GF50/80, 50 minutes BT (25 at each depth)

130 - 90, 109 minutes
90 - 130, 119 minutes
 
Best mix is awesome on paper. Not so much after your sites change or you get blown out and the best mix in your tanks isn't the best anymore.

I haven't done a dive on best mix yet where I didn't factor possible alternative sites into the planning. That was part of the training. Best mix is "best" based on a lot more factors than simply the planned maximum depth of the planned, first choice dive site.
 
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