What was the old Bill Royal algorithm? Dive till it hurts, hang till it stops?
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What was the old Bill Royal algorithm? Dive till it hurts, hang till it stops?
Granted that I am only doing Nitrox above 130'.
I have been using Buhlmann computers and adding "Pyle" deep stop (safety stop).
Given that I am using redundant computers that track any slow tissue "on-gassing" or reduced off gassing that results from extra safety stops, AND factor extra tissue loading into my decompression obligation-
Can anyone offer reasonable thoughts as to potential "down side" of extra safety stops? Other than extra 5 min deco time.
I see absolutely no contradiction to adding a bit of RBGM onto a gas model. I have never seen an argument (aside from added time) that says you HAVE to take your supersaturation right up to the limit when using gas model decompression.
http://www.rebreatherworld.com/showt...rs-for-DummiesQuote:
Originally Posted by GregO
http://www.diverite.com/articles/gradient-factors/
https://decodoppler.wordpress.com/20...lified-primer/
http://www.alertdiver.com/Gradient_Factors
There's a great article written by the GUE folks on it, too... but I can't find it and I'm at work and should be doing... you know... work.
Edited to add: I found the GUE article I was thinking of. It had nothing to do with gradient factors at all. (Unsurprising, really. I don't know why I thought GUE would be writing anything about GFs.) It was about hyperbaric oxygen.
Quote:
Originally Posted by GregO
Here you go:
"Gradient Factors for DummiesGradient Factors for Dummies
By Kevin Watts
This article attempts to provide a user's view of gradient factors, an Erik Baker derived method of calculating decompression schedules. The title is not meant to be derisive, but simply an indicator that this article is meant to be a primer.
Back to Buhlmann
Everything in the gradient factor decompression algorithm revolves around Buhlmann’s tissue model. Currently this means 16 hypothetical tissue compartments (TCs) that are constantly tracked during a dive in order to determine each TC's inert gas pressure.
As you ascend all those TCs start to release pressure ("off- gas"). The question is "How fast can you let those TCs off-gas?"
Buhlmann answered that question by coming up with an “M-value”. Basically, an M-value is a maximum pressure value (different for each depth and tissue compartment) that tells you, if you exceed that value, Buhlmann thinks you’re crazy and believes you're about to get bent.
A natural ascent strategy, then, would be to move up in the water column until the pressure in your TCs just reaches Buhlmann’s M-value and then let your TCs off-gas a bit, rise to the next level, etc. In this strategy, you would keep going up in such a way that you never let your TCs exceed Buhlmann’s M-value.
Unfortunately, decompression illness does not exactly track Buhlmann's M-values. More sickness occurs at and above the pressures represented by M-values and less sickness occurs when divers never reach Buhlmann’s M-values.
Enter Gradient Factors
Gradient factors (GFs) were invented to let the diver choose how fast, and how close, their TCs get to Buhlmann’s M-values.
Gradient factors are calculated as follows:
What does this formula tell us?
First, the gradient factor formula tells us that at a GF=1.0, you are at Buhlmann’s M-value. Therefore, staying at or below GF=1.0 seems important. Second, it tells us that when our tissue compartment pressure just reaches ambient pressure, then the GF=0.0.
Another ascent strategy, then, might be to shoot up to a GF=0.8 and ascend in such a way as not to exceed that value. In this way you know that your tissue compartments are never over 80% of the distance between ambient pressure and Buhlmann’s M-value. In essence, you have a 20% safety margin on Buhlmann's M-values. Dive computers implementing GFs usually let you set two GF parameters. Moving straight to GF=0.8 and ascending in such a way that you always keep your TCs at GF=0.8 would be equivalent to setting your dive computer to 80/80.
Erik Baker's Strategy
Erik Baker didn't like the idea of ascending directly to a GF close to Buhlmann's M-Value. Instead he said, “Let’s all ascend first to a lower GF, then slowly move to higher GFs.” So, let’s say you want to first ascend to a GF=0.30 and then slowly move to reach GF=0.85 as you surface. This setting on your gradient factor computer is 30/85. In fact, my Shearwater computer uses 30/85 as it's default setting.
So what is happening when you use a GF setting of 30/85?
First your dive computer allows you to ascend until the pressure in your TCs first reaches a GF=0.3. This means your TC pressure is 30% of the way between ambient pressure and Buhlmann’s M-value. Then you sit there until your TCs drop enough pressure so that you can ascend to your next stop.
How much pressure must leave your TCs before you can ascend?
Assume you hit your first stop (GF=0.3) at 110 ft. Well, then, we now have two known points. Point 1 is (110,0.3), that is, at 110ft we are at a GF of 0.3. Point 2 is (0, 0.85), that is, at the surface we want to be at a GF=0.85. A natural way to ascend (and this is what Baker did) is to create a line from those two known points and ascend in such a way that you never exceed the GF generated by that line.
Once you've determined your two points, the formula for the maximum GF at any depth is:
But, since the high gradient factor is reached at the surface, HiGFDepth=0. So,
Therefore, if you hit your first GF=0.3 at 110ft, then your LowGFDepth=110. Before you can ascend to 100ft you must let off enough TC pressure so that when you arrive at 100ft the GF of your TCs does not exceed 0.35 calculated as
You can ascend to 90ft when your TCs let off enough pressure at your 100ft stop so that when you reach 90ft your TC's GF does not exceed 0.40 calculated as
The GF method allows you to ascend by walking that line all the way to the surface.
Summary
If you understood the above explanation, then you see why divers on RebreatherWorld say that setting your GF parameters to 10/90, or 10/80, etc. helps generate deep stops. The low GF of 10 means a stop must be generated when your TCs are only 10% of the way between ambient pressure and Buhlmann’s M-value, rather than 30% if you were to set the low GF to 30. Simply, the GF line just starts deeper.
The gradient factor method is a natural extension of Buhlmann's tissue compartment model. Diver's using computers implementing the gradient factor method should understand how modifying their GF parameters will alter their decompression profiles. My understanding is that it may be wise to consider altering your GF parameters based on dive characteristics, your physical condition, and your general attitude toward the risk of decompression illness. The gradient factor method provides the diver substantial flexibility in controlling their decompression profiles. Your responsibility is to choose the factors appropriate for you."
And obviously the Master piece.. not that difficult to follow either..
http://wrobell.it-zone.org/decotengu...ds/mvalues.pdf
and no offence intended, but when any diver has difficulties following and understanding these, such diver should cautiously limit their deco obligation, better not do deco overall..
That is my opinion to it
In regards to the poll. I opted for GF, favor shallow stops given the latest and greatest feedback in research and as a result positive results from divers changing their approaches.
I used to do the exact opposite though when I started, I chose my strategy favouring deeper stops and I even added Pyle stops on top of that in between..
I think the poll is a bit misleading as there is no such thing like "even GF".. I am not sure Jax how you chose the examples, but the even seem to match 100 overall when you actually add the numbers..
The favour shallow stops seems to exceed 100 while the favour deep stops seems to stay below 100..
Might be complete coincidence, might be a system..
Just a few comments to that.. when I alter/shift my stops from one side towards the other from a proven concept, then I try maintain the same overall decompression time a my overall concept..
So when I want to move my stops shallower I start moving up the low GF and then I resolve the hi GF to a value where I am close to the overall decompression time..
Doing it anyway different like just pushing up the Low GF and keeping the high GF at the old number etc.. will not only cause your depth of the stops being moved but you ARE EFFECTIVLEY changing the overall conservatisim of your decompression!
So one needs to be aware of that playing around with theses values..
Also apart from the choice of Lo GF + high GFs one needs to make up their mind on ascent speed before the first stop and between stops..
Here is something I have adapted from the (proven by the many dives conducted in the community as also succesful) Bubble model approach.. Rather than doing deep stops I am doing a consciously slow ascent until the first stop.. With Trimix there is the not faster than 10m/min recommendation anyways and that is what I do on Trimix but also on air I am not going faster..
Ascend speeds to your first stop will impact your feeling after decompression as well.. and maybe doing a slower overall ascent to first stop can eliminate the "need" for deepstops for you as well..
The default settings tend to be 30/70, and some people go with 20/80, etc. to set their range an equal amount less than the 100% line and above the 0% line. I don't know what to call it, but if anyone has a name for that????Quote:
Originally Posted by Nitrogenius
The two numbers don't really relate to one another and there's no reason to add them together, if that was where you were going?Quote:
Originally Posted by Jax
+1Quote:
Originally Posted by oya
so my observation on selecting these examples was correct..
of course the numbers relate to each other as they reflect the lo GF and the high GF so to some extend the frame you want to decompress in, but the relate to the M Values..
So a GF lo is not equaling a GF lo directly.. It takes a certain state of saturatuion that needs to be aqual as well in order to compare the two..
The same applies to the hi GF..
Even more you cant directly correlate the lo GF to the hi GF as the high GF very very sure will relate to a different M value as in fact your lead tissue will have shifted over the course of your decompression..
That is why I am dead serious about making sure to understand GF and understand M Values when you chose to use this decompression concept and even fiddle with it.
It has nor merit and value to add GF lo and hi to reach 100 and to stay over or under it..
Staying over it does not shift to shallower decompression and staying under 100 does not lead to deeper stops..
The depth of your first stop is only being affected by the GF lo.. the GF hi is irrelevant at this point (at least to the most extend it is soon coming into play determining the length of your first stop as you will need your terminal GF established to distribute the rest of the stops hence determining the length of each particular stop involving the GF concept)
There is some certain rule of thumbs approaches that involve looking at adding those to numbers and comparing them within a very limited frame, but essentially it really has NO MERIT whatsoever to add those numbers..
If at all you can characterize:
GF lo sets your relative depth of starting your decompression stops
GF hi sets your relative conservatism, but be weary that one influences the other so GF X/70 vs GF Y/70 never does represent the same level of conservatism of your overall deco.. The only thing it says is that your LEADING Compartment will have an MValue of equal or lesser than 70% of its allowed highest value according to Buhlmann original values..
It has no meaning as to the saturation level of other compartments (here the detail of the dive profile and decompression profile kicks in toghether with distribution over stop depths) other than being sure that no other compartment exceeds 70% of its permissible max M-Value...
To compare overall conservatism of decompression playing around with GFs the only method is to stay within the same overall decompression time umbrella.. this is how you shift from shallow to deeper stops and vice versa..
So the closest approach to the concept of an "even GF" would be to set a certain overall time you want to decompress in relation to a certain dive profile..
Hope this helps..
Negative.Quote:
Originally Posted by oya
There simply are people that move their gradient factor choice the same percentage from the absolute.