Slow tissue on gas from stops
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After making enough deco dIves with similar depths and run times a lot of people start to know what the stops will be before involving a computer. This isn't magic or inneficient, it's experience. Experience comes in handy as it can tell you if something seems off.
I completely agree, your body and your experience will tell you if something is off and of course we get used to certain stops at certain depths for repetitive dives. But I think you may be conflating this with the issue of the efficacy of RD over either using a computer or using a 2nd computer and therefore the need for RD. There is no data available that I am aware of that shows a significant failure rate of dive computers. Divers may have programmed them wrong but that's just user error.
PfcAJ
Contributor
Well of course it’s an error. Obviously. But the point is that the error *can* happen.
UTDs take on ratio deco is clearly not the most efficient ascent solution. You can get a more efficient ascent using a computer.
However, with some careful study and minor adjustment you can get an ascent schedule based on a ratio that’s pretty darn close to a computer generated schedule.
If your ratio method for coming up with an ascent schedule closely mimicks the computer but affords you the ability to predict the required deco for certain time and depth combos, why would you *not* want that knowledge?
I much rather would want to know more things and have more tools than less.
Jack Hammer
Contributor
For clarification, I don't believe RD, in any variety, is "efficient" at all, especially as taught by UTD and extra especially as a primary planning tool. It may be semantics, with experience some people notice a relationship between the amount of time spent at a particular depth and how much deco time tends to rack up for that time. This comes from experience and can be a handy piece of knowlege when weighing how you want to proceed during a given dive. E.g., "Checking out that row boat down there ain't worth spending an extra 10 mins of deco in 39f/4c water".
PfcAJ
Contributor
Again, you could have 10 computers. Not a one of them can tell you what your deco would be if you went 20ft shallower than where you are currently. They aren’t predictive, especially not on dive mode past perhaps the +5 and delta5 options on a shearwater.
RD is predictive.
I can have more than a fair idea using sound (not UTDs methods...) ratio deco techniques. Within a minute or two or what my computer box says. That’s good stuff.
Ok you lost me on the predictive stuff. I use a CCR on all my dives. RD is simply not accurate enough to justify me risking my health using it to plan the ascent. Also and I stand to be corrected but Simon Mitchell mentioned in one his previous posts that there is NO scientific paper that validates RD, that is how inaccurate it is. So I'm seriously impressed if you can plan in your head your deco obligations on a multi gas dive where because your on a CCR you stay a bit longer or go a bit deeper than planned.
PfcAJ
Contributor
Real life example time:
We’re scooterin around a wreck at 150’. We’ve seen what we wanna see and decide to scooter over to another wreck just east of wreck 1 at 130’.
If we spent 10mins on wreck 1 I know how long we can spend at wreck 2 before we hit our max allowable deco time. Is it worth it to go over there? How much more bottom time will we get for going 20’ shallower?
Your computer can’t tell you that beforehand.
We’re scooterin around a wreck at 150’. We’ve seen what we wanna see and decide to scooter over to another wreck just east of wreck 1 at 130’.
If we spent 10mins on wreck 1 I know how long we can spend at wreck 2 before we hit our max allowable deco time. Is it worth it to go over there? How much more bottom time will we get for going 20’ shallower?
Your computer can’t tell you that beforehand.
PfcAJ
Contributor
I lost you because you don’t know anything about RD but hold strong beliefs on its utility.
I’m going to attempt to help you.
A certain algorithm (gradient factors of your choosing, this is hypothetical) gives you 30mins of time on 50% after spending 30mins at depth. You adjust your bottom time and see that 25mins at depth results in 25mins of deco, and 35mins results in 35mins of deco. That “ratio” is 1:1. You verify it across a range of times and see the limits of that ratio. That’s it.
Now do you it with different depths. Maybe 10ft shallower consistently results in 5mins less time on 50%. Or maybe 10ft deeper consistently results in 5mins more time on 50%. Verify for different times. Now you have a simple adjustment to your ratio we established above.
Which method now is more accurate if both methods come up with the same result? The algorithm baseline or the ratio method?
You can use these simple trends to predict your deco time before you splash and also use it to predict your deco time during the dive.
It’s not some crazy thing PROVIDED you’re using an algorithm as your baseline (like buhlmann 40/85, for instance).
Jack Hammer
Contributor
AJ is talking about using a depth time relationship to guesstimate how changes to the dive profile will affect the overall deco obligation. He's definately not talking about using RD as taught by UTD.
I'm a bit surprised that diving a CCR you seem unaware that with deco there is a relationship between time and depth. This is part of the simple basics for deco algorithms.
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