What is Ratio Deco?

[PfcAJ]

DecoPlanner does not do that, and I don't think it should

"Ratio deco" can be a lot of different things. For instance, I outlined above how both a 150ft dive and a 130ft dive can be a "1:1" ratio, but the dive parameters are wildly different (different gases, hugely different bottom times). I could also adjust my gradients and come up with a different ratio.

 

[kr2y5]

DecoPlanner does not do that, and I don't think it should

Why not? For those who are skeptical about the validity of plans generated by ratio deco, because they are not sure whether the specific profile is well within the limits, within the rule of thumb approximation works well, would gain a peace of mind. I, for one, would start to use ratio deco on every dive if I had confidence that within some range of parameters, it does not deviate from what a real model would compute.

 

[LiteHedded]

Why not? For those who are skeptical about the validity of plans generated by ratio deco, because they are not sure whether the specific profile is well within the limits, within the rule of thumb approximation works well, would gain a peace of mind. I, for one, would start to use ratio deco on every dive if I had confidence that within some range of parameters, it does not deviate from what a real model would compute.

all you have to do is plan a dive with both methods and compare...
if you take a gue tech class you will do a lot of this

 

[kr2y5]

all you have to do is plan a dive with both methods and compare...
if you take a gue tech class you will do a lot of this

Yeah, but you'd have to compare them for every possible deviation from the plan to really be 100% sure that if you make adjustments, you will end up with the same result as what the real model would compute. At least you'd know how much adjustment you can safely make on the fly using this method, and at what point it breaks.

 

[PfcAJ]

Why not? For those who are skeptical about the validity of plans generated by ratio deco, because they are not sure whether the specific profile is well within the limits, within the rule of thumb approximation works well, would gain a peace of mind. I, for one, would start to use ratio deco on every dive if I had confidence that within some range of parameters, it does not deviate from what a real model would compute.

I'm telling you that it does deviate. But at some point that deviation can be expressed with a different ratio.

The point is to learn the trends yourself and use your noggin, not have something tell you the answer. Its the same reason why I don't use a dive computer. I believe there is benefit to analyzing the outputs and identifying the ratios and where it breaks down.

 

[LiteHedded]

Yeah, but you'd have to compare them for every possible deviation from the plan to really be 100% sure that if you make adjustments, you will end up with the same result as what the real model would compute. At least you'd know how much adjustment you can safely make on the fly using this method, and at what point it breaks.

I think you should take a tech 1 course. it would answer a lot of your questions

 

[huwporter]

The Buhlmann equations are quite achievable to programme an implementation of yourself. I've written a couple of implementations of Buhlmann ZHL16 (one in Excel, one in SQL) for the purpose of evaluating what the theory thinks about the ratio deco ascents that I was actually doing. (They work in the opposite way to a traditional deco planner - they make no attempt to calculate a profile for you; you start with a profile, and the implementation tells you what gradient factor you are at at each stage.) Off the back of that, I'm personally happy with the 'well known' ratios within their stated ranges of appliccability (and have a few additional personal ratios for profiles outside those ranges).

Most conventional deco planners can also be fudged to evaluate a specific ascent schedule - just add a whole lot of additional levels on apppropriate gasses, and see if the planner starts adding additional stop time over and above the 'levels' you have added. Be aware that some planners have unspecified settings and assumptions that can cause funny results with this (part of the reason I wrote my own - to know exactly what and how assumptions were being applied).

Cheers,
Huw

 

[ajduplessis]

It is something that can be used on the fly. What if all of your computers fail (maybe one floods and you lose one)? What if you miss your depth or over stay your planned dive time? It is a way for a diver to plan a deco schedule on the fly with nothing more than his brain.

I don't use RD and don’t intend on using it as the system does not suit my requirements. I also struggle to understand why you want to deviate from agreed dive plan It goes against my diving philosophy, planning and strategies. IMO a DC is not your primary strategy to get out the water. You use the calculated run on you slate with a BT!

No to answer your questions/comments: If your DC fails you follow the run on your slate and BT. If you miss your depth or over stay your planned time, you should rather stop diving!! If you can’t control every aspect of your planned dive, rather stay out the water IMO. This is in a world without problems……

In the event where an emergency forced you to deviate from the agreed and planned dive profile, you switch to the backup tables in your pocket. Stresses and time pressures from altered dive plans can and will cause mistakes in calculating RD profile to get out the water. This even happens without any stresses or emergencies.

Every diver needs to see and understand the bigger picture to mitigate the risks involved with the type of diving they do….. and then accept the consequences.

 

[CptTightPants21]

It is easy to call someone who has a change in dive plan an idiot and that they should stop diving, but that is a gross over simplification. Just off the top of my head, what if a person gets tangled in fishing line, wires or something in a wreck, mucks up a reel and needs to fix it. There are loads of situations that could cause a person to overstay or change their dive profile and still not create a serious risk to their life.

I know a story of one dive buddy who dropped his reel on a wreck and needed to go 20 ft deeper and a little bit inside the wreck to get it, probably took 5 minutes, but that is enough to change a deco profile when you are already at 110ft.

 

[ajduplessis]

Did you actually read my response? Getting entangled (your example) in my part of the world is an emergency, until resolved..... Dropping a reel is being an idiot! Anything else I need to clear up for you?