Ratio deco #1

[rjack321]

There are computers available now which can run straight Buhlmann GF, such as the Liquivision or Shearwater. The proper choice of gradient factors(30/85 sticks in my mind) should bring you close to what you would get from Ratio Deco.

Not even remotely close. Timewise its fine. There's alot deeper stops in RD and Buhlmann with 30/85 (or any other GFs) will not give you credit for those. Net I'll be stopping about 60ft deeper than you. You'd be sitting at 10ft for another hour while I'm on the boat.

The X1 with V-planner is vastly better if you have a compelling need for a computer as the VPM algorithm will give you credit for the deeper stops (Buhlmann actually penalizes you both for the deeper stops and the He)

 

[ucfdiver]

You'd be sitting at 10ft for another hour while I'm on the boat.

Depends on the dive. Nearly all my dives are shorter using VPM+2 or 20/85 than ratio deco.

 

[rjack321]

Depends on the dive. Nearly all my dives are shorter using VPM+2 or 20/85 than ratio deco.

Shorter runtime? Compared to 20-40min bottom times in the ocean you are skipping RDs deep stops or something. Or maybe skipping the extended 75% deep RD stops(?) which do get pretty long IMO when you're an hour+ over MDL.

I do slightly more shallow time than RD would suggest. By trial and error VPM +3 runtime seems about right for me and trimix dives. Oddly (I guess) I can be more aggressive than RD on nitrox deco dives (<100ft stuff), more like VPM +1 runtime.

Buhlmann will go rediculously long at some point and I haven't looked at a GF output in years.

 

[ucfdiver]

Shorter runtime? Compared to 20-40min bottom times in the ocean you are skipping RDs deep stops or something. Or maybe skipping the extended 75% deep RD stops(?) which do get pretty long IMO when you're an hour+ over MDL.

I do slightly more shallow time than RD would suggest. By trial and error VPM +3 runtime seems about right for me and trimix dives. Oddly (I guess) I can be more aggressive than RD on nitrox deco dives (<100ft stuff), more like VPM +1 runtime.

Buhlmann will go rediculously long at some point and I haven't looked at a GF output in years.

I don't think it's odd on nitrox dives, I just think that the longer the dive, the more distorted ratio deco becomes, as it's shoving a logarithmic equation into a linear formula. But heck, it saves grabbing a set of tables out of the wet notes

 

[Blackwood]

Yah, long profiles (more than about 40-45 minutes are out of the ratio deco "sweet spot." There is no accounting for exponential loading; it's all linear (as James noted).

Hardly seems the most reasonable for long cave-like profiles.

 

[ucfdiver]

Yah, long profiles (more than about 40-45 minutes are out of the ratio deco "sweet spot." There is no accounting for exponential loading; it's all linear (as James noted).

Hardly seems the most reasonable for long cave-like profiles.

It's logarithmic...slows over time!!!

(OK, this is a who cares thing....but I wanted to use the new smiley)

 

[rjack321]

I don't think it's odd on nitrox dives, I just think that the longer the dive, the more distorted ratio deco becomes, as it's shoving a logarithmic equation into a linear formula. But heck, it saves grabbing a set of tables out of the wet notes

Let me phrase that differently:
On trimix I am have to be more conservative, roughly VPM+3 on runtime or RD plus 5mins of O2 time.

I can be more aggressive than RD or VPM+3 on nitrox, roughly equal to VPM+1 on runtime.

 

[ucfdiver]

Let me phrase that differently:
On trimix I am have to be more conservative, roughly VPM+3 on runtime or RD plus 5mins of O2 time.

I can be more aggressive than RD or VPM+3 on nitrox, roughly equal to VPM+1 on runtime.

Are the mix dives shorter than the nitrox dives? What happens when you do similar length on mix? (just a guess here)

 

[Blackwood]

It's logarithmic...slows over time!!!

Math =/= scuba lingo.



But if we're being picky, I want to use that smiley too.

...ratio deco becomes, as it's shoving a logarithmic equation into a linear formula.

Ratio deco is shoving a linear equation into what is conceptualized as a logarithmic process. Not the other way around.

 

[rjack321]

Are the mix dives shorter than the nitrox dives? What happens when you do similar length on mix? (just a guess here)

Yeah generally shorter and deeper (190; for 25 on 18/45) on mix vs. longer and (relatively) shallow (100' for 60 on 32%). Although light helium mixes (25/25) and pretty long for around here (90' for 70mins) seem to be more like nitrox.

Its not really a RD thing as the same pattern is seen with VPM. Net, I don't think the "helium advantage" applies to me & my scar tissue.