Ongoing discussion of Ratio Deco

[rjack321]

above numbers seem to indicate that RD is a "bit" less conservative than V-planner (+2).

All well and good, but what makes V-planner +2 the standard against which to measure? Why not +3 or -1?

(Don't have it myself to compare)

 

[grazie42]

Because it is what the authors of RD suggest? (1st paragraph-overview in the paper)

 

[rjack321]

Because it is what the authors of RD suggest?

Didn't notice that line in there before. Like I said earlier, I was a pre-NAUI student

EDIT
It would be nice if someone with access to GF decoplanner (I'm at work right now can't you tell?) could compare across all 3 approaches in a table.

 

[ScubaMilo]

Nicely put Clare.


Tobin

Finaly we agree on something, Tobin!!!

Thanks, Clare for helping clearify what we have been saying.

Milo

 

[grazie42]

Originally Posted by rjack321
It would be nice if someone with access to GF decoplanner (I'm at work right now can't you tell?) could compare across all 3 approaches in a table.

I agree...I´ve been curious about GF-sw for a while but not curious enough to spend 150$ to check it out (V-planner is 80$ and includes continous upgrades )...

 

[amascuba]

Seems to me that we are arguing which is the best flavour of ice cream here*

Ratio deco has it's uses - and when I dive within a certain window it is a pretty good tool to use. The question is where is the window?

A 45 metre (150ft?) dive for half an hour is perfect for Ratio Deco. Push much longer or much deeper on one deco gas and it starts to get cumbersome and inaccurate (around the depth we would change the set point). Longer deco is not always better - particularly in deep stops and care must be taken on dives which are particularly short (deep) or long (shallow) to get these in the right region. It can be done with good understanding of the desired outcomes but for this Ratio deco must not be used as a blunt instrument - it requires more refinement that this.

To inform yourself whether the dive you are planning is within the window you can either rely on previous experience or use as much information from as many sources as possible to get ideas of loadings prior to the dive.

I dive very regularly in the 40 - 70 metre range (130 - 230 feet) and operate Ratio Deco in water (with a few tweaks) but prior to a new dive profile I use every bit of information that I can lay my hands on to play with deco, run scenarios, look at various failures and study loadings, gas use etc.

For this I use Decoplanner but I can also use V planner, peer experience and my own experience when looking at planning a dive. GUE does not ask me to be wedded to one way of calculating deco - far from it - it asks me to be a thinking diver who takes my safety and that of my team very seriously indeed.

Checking plans for dives which are on the edge of our experience curve in as many ways as possible is one way that I can try to D.I.R.

Good debate though guys - interesting reading.

*although everyone should know that is always chocolate

Excellent post Clare. Thanks for contributing.

 

[Phil K.]

Ratio is never more than 1 minute LESS than decoplanner. It may be more conservative. And you need to add it the deep stop times.

Rjack,

You were on a roll until you failed to harmonize your bogus assertion to Scuba Milo's demonstration of a profile where RD is 500% less conservative than D Plan (GF=30/85). What's 5 minutes more or less? Did you just clock out on that one? Until Milo shot it down, you had me convinced that RD is a close approximation of the other scientifically derived algorithms. As can be readily observed by working out a few profiles on D Plan, sometimes RD produces a close approximation and sometimes it doesn't. It's frequently validated as an approximation of other algorithms, which means that it's an approximation of an approximation.

Furthermore, you haven't addressed the limitations on dive planning caused by RD's reliance on standard gas mixtures or does your adherence to RD go so far as to supplant any thought of a mission where optimal BT/DT requires customized mixes? Using RD can you give me a schedule for 8 repetitive gas dives over 3 days with a max depth of 250fsw on Trimix 16/55 EAN36 and 100 O2. SIT(1) three hours and thereafter increasing 2 hours between subsequent dives assuming a dive SAC =.80/deco SAC = .30?

 

[amascuba]

Furthermore, you haven't addressed the limitations on dive planning caused by RD's reliance on standard gas mixtures or does your adherence to RD go so far as to supplant any thought of a mission where optimal BT/DT requires customized mixes? Using RD can you give me a schedule for 8 repetitive gas dives over 3 days with a max depth of 250fsw on Trimix 16/55 EAN36 and 100 O2. SIT(1) three hours and thereafter increasing 2 hours between subsequent dives assuming a dive SAC =.80/deco SAC = .30?

*cough*DIR Forum*cough*

In all reality, would you really expect somebody in this particular forum to discuss the limitations of Ratio Deco for using non-standard gases?

 

[ScubaMilo]

*cough*DIR Forum*cough*

In all reality, would you really expect somebody in this particular forum to discuss the limitations of Ratio Deco for using non-standard gases?

I believe Phil K. is just trying to point out the limitations of ratio deco.
And, believe it or not non standard gases can be DIR (Take a look at some deep cave explorations ie: WKPP, EKPP).
Standard gases can be determined by the team who is doing the dives.
These guys are using "nonstandard" gases to fit the profile of the dive.

So I believe that talking about "non standard gases" is is not outside the realm of this forum.

Unless you would say the WKPP is not DIR?

Milo

 

[Phil K.]

In all reality, would you really expect somebody in this particular forum to discuss the limitations of Ratio Deco for using non-standard gases?

Yeah, absolutely. If RD is based on standard gas mixes, but produces results that can only be duplicated with other algorithms using nonstandard mixes, what conclusions do you draw? Let me guess: RD is right and the others are "wrong." Bro, they're just numbers generated by a formula. An approximation of an approximation can't be more accurate than what it's trying to approximate.

BTW, I take that as a "no."