Ratio deco

[Blackwood]

However, strictly speaking, I think it is possible to use Ratio Deco to plan a dive and then simply stick to the plan.

Of course it is. It's crucial to do so for gas considerations.

If I go do a dive this weekend nominally to 150' for 30 minutes am I going to pre-plan it? No, I've done it enough that I know how much gas I'll bring, which gases to bring, what deco schedule I expect (1-1-1-1-4-4-2-2-3-10-5), and what the limits are.

However, chances are it won't actually be 150', or 30 minutes, or both, and I'll use RD 'on the fly' to correct my schedule, and to determine whether I have adequate gas to extend the dive time or increase the dive depth.

OTOH, if the nominal plan is for a profile I'm not familiar with, I will pre-plan it (ratio deco is my primary method, but for stuff outside my current comfort zone, I'll also compare VPM and Buhlmann algorithms).

 

[ucfdiver]

Thanks for the link, though you're first bit of advice looked good too. What happened to that post???

I figured it might be a bit too tongue in cheek so I edited it.

But in all seriousness, some of the people who have posted advice in this thread have been bent like a pretzel, do you really want to take advice from them? Furthermore, after being bent, they even posted on UTD's forum that they're doing it correctly using deep air!

 

[wrybosome]

I highly suggest a good decompression course before attempting any of this, as the consequences of botching it can be quite severe (nerve damage, paralysis, death, etc).

Thanks, I wasn't planning on trying it out w/o training (almost put a disclaimer in the original post). Like a VFR pilot who wants to understand how instrument landings are done, I'm just curious. Both about how the various models work, what the reasoning behind them is.

Thanks everyone for giving me a good starting point on this.

 

[LiteHedded]

Thanks, I wasn't planning on trying it out w/o training (almost put a disclaimer in the original post). Like a VFR pilot who wants to understand how instrument landings are done, I'm just curious. Both about how the various models work, what the reasoning behind them is.

Thanks everyone for giving me a good starting point on this.

it's dangerous even with training. caveat emptor

 

[ucfdiver]

Thanks, I wasn't planning on trying it out w/o training (almost put a disclaimer in the original post). Like a VFR pilot who wants to understand how instrument landings are done, I'm just curious. Both about how the various models work, what the reasoning behind them is.

Thanks everyone for giving me a good starting point on this.

The UTD classroom does every bit as good explaining WHY as it does HOW. It covers the history of several algorithms, explains the "s curve" or "reverse curve" pretty well, as well as the o2 window pro/cons. You'll walk away with a better understanding of deco regardless of which algorithm you use after the course.

 

[Web Monkey]

Thanks, I wasn't planning on trying it out w/o training (almost put a disclaimer in the original post). Like a VFR pilot who wants to understand how instrument landings are done, I'm just curious. Both about how the various models work, what the reasoning behind them is.

Thanks everyone for giving me a good starting point on this.

Ratio Deco is an interesting concept, and there are people who use it exclusivly, but I'm a lot more comfortable calculating a plan on vPlanner and taping it to a wrist slate.

Your mileage may vary.

Also, FWIW, someone mentioned using a computer for deco dives. This may just be my overly-cautious side showing, but I'd much rather trust the computer on my desk and a printed plan than a computer on my wrist underwater.

While it's nice if a computer can get you out of trouble if you manage to screw up and incur an unexpected deco obligation, I've seen too many computers say "E7" or "Signal Lost" or simply go blank at inopportune moments to assume it's going to work flawlessly when I need it.

At least with a wrist slate, you know what the plan is, and know that it won't vanish.

Terry

 

[wrybosome]

it's dangerous even with training. caveat emptor

Gotcha. Like I said, my interest is theoretical right now.

Our dive club had a speaker from Suunto a few weeks back who went through how the N2 loading model they use works. 9 tissue compartments with different loading/unloading speeds, etc. It reminded me very strongly of models we use in my work. I do drug dosage design, and for simulating the expected pharmacokinetics we use a compartment model that combines broad assumptions about 'average' physiology and biochemistry with info about drug solubility, protein binding, etc to predict drug serum levels over time. But we know better than to assume the model is anything more than that. Our mileage varies significantly because reality is messier than that. The deco models reminded me of that.

The UTD classroom does every bit as good explaining WHY as it does HOW. It covers the history of several algorithms, explains the "s curve" or "reverse curve" pretty well, as well as the o2 window pro/cons. You'll walk away with a better understanding of deco regardless of which algorithm you use after the course.

Thanks, signed up and will go over it this weekend.

 

[JeffG]

At least with a wrist slate, you know what the plan is, and know that it won't vanish.

Terry

Who says you can't write the Ratio Deco Plan into your wetnotes?

 

[H2O 70]

I would just like to add that this has been a uber useful thread. A couple of weeks back, Blackwood had posted something about Ratio Deco. Found it on Wiki, however it was lacking.

Saw the UTD had a class for it, but I didn't pursue it further.

If you take the UTD class on Ratio Deco, can you apply that to future UTD certs? Just curious.

 

[Web Monkey]

Who says you can't write the Ratio Deco Plan into your wetnotes?

There were two separate thoughts:

1. I don't trust Ratio Deco
2. I don't trust dive computers to not fail.

Terry