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Ok

Have been reading the articles on deep stops and I understood the Richard Pyle bit about practical experimentation developed his thinking and fish stops led to a decrease in micro bubble symptoms like lethargy etc... No worries

and I think Andy H told me that stops could be at 80% of the max dive depth and so on.

But I cant understand the article on pressure gradients and deep stops...Can anyone explain it in simple terms??
For one poor cognatively challenged diver??

Stevie W probably understands it cos he's clever,
sigh
but I, at the moment, cant!!!

any help?

Ian

 
 

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The "No Science At All Version".

Take a bottle of coke and shake it up.  Now, if you loosen the top, it'll try to fizz over, but if you tighten it again quickly before it gets to the top, you can prevent the fizzy mess and wait for the bubbles to go away, then repeat the cycle until you can open the top safely.  That's kind of like the Buhlmann tables, depressurise until you are about to bend then stop and de-fizz.

Deep stops figure that you need to be a bit more sensible, and never let the bubbles get near the top of the neck.  Doing deep stops are like loosening the cap gently and only letting a few bubbles form.  The gradient factors are a mathamatical way of saying how fizzy it is allowed to get before you have to stop, and how much they have to subside before you can start again.

Pyle stops you can do in your head, but Eric Bakers gradient factors are too much maths to be doing under pressure (but would appear to be better) so don't worry about the maths bits.
 

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Ian
I was intigued so I checked the web for an explantation. GF are quotes as 80/20 meaning percentages. Each one modifies a standard deco schedule and are applied to the deep and shallow stops respectively. From what I could gather a standard schedule is modified to add deep stops, but the theory goes that a long deep stop will alow off gassing of some tissue compartments but on gas other tissue compartments to near their max. So long stops are reduced using a gf this is the first figure (e.g. 80) the second figure (20) is used to modify the shallow stops. Between them they should give a better chance of avoiding dcs, but as you know the science is not proven.
If I have mis-understood that can someone let us both know, as I have to be honest it was a bit heavy.
Matt
 

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I've been told to do a stop at 2/3 of your current depth
 e.g. Your at 45mtrs, 2/3 of 45 is 30, sensible ascent to 30mtrs, stop for 1min, 2/3 of 30mtrs is 20, sensible ascent to 20mtrs, stop for 1min, 2/3 of 20 is 13, sensible ascent to 13mtrs, stop for 1min. Start your deco proper at 9, 6 and 3mtrs.
 You'll probably pick up a bit more deco at 9,  6 and 3 but because of the stops the bubbles will not grow too rapidly in your system as they would have if you went straight from 45mtrs to 9mtrs in 5mins or so. It gives you're body a chance to start flushing out any microbubbles that are being released from the greater depth pressure on the way upstairs. I suppose this is just a simplified Pyle stop method.

Peter
 

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(Not correcting you, Matt, just saying a bit more on the subject.)

The "Some Science Version".

When you do deco dives, you have a "virtual overhead situation", there is a virtual ceiling which is the point at which  the equations say you will get bent if you go over.  The ceiling gets higher as you decompress.  Eventually it breaks the surface and you can get out.  The way deco software/tables work is that they pick a convenient set of steps for the stop depths, and keep you at each stop depth until your ceiling clears then next one, whereupon you ascend to it.

If you have been reading the articles, then you will have come across the "M-Value line" and the "Ambient Pressure Line"  The M-Value line is the Buhlmann ceiling, the Ambient Pressure Line is wherever you happen to be.  The Gradient Factors represent where the ceiling you are using lies relative to these two lines.  Zero means the Ambient pressure line, and 100% (or 1.0) means the M-Value Line.

The deepest possible stop is the next stop depth after at least one bit of you could possibly be considered to decompress and is the point at which the Low Factor is applied, the shallowest stop is the point at which the High Factor is applied.  

These two points define a line themselves which represents the ceiling you are using for the dive. The line maintains a smooth change from one factor to the other, so only the High Factor actually applies to a real stop since stopping at the deepest possible stop isn't usually sensible.  Using 0/0 would mean that you could never ascend since your ceiling is always your current depth.  Using 100/100 is the same as normal Bulhmann stuff.  

Using 80/20 means that you are pulling back a bit from Buhlmann's ceiling at the shallow stops, but are really conservative at depth, thus you get deep stops, but aren't penalised when you get shallow like you would if you just made the Buhlmann equations more conservative.

Caveat emptor.
 

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Thanks Guys!
I am actually starting to understand the theory! though Im not going to attempt to summarise it. Still, I like to understand the theory behind the practice.

and Im grateful for the practical tips, will use the 75% depth principle. I guess my only question is what constitutes deep versus shallow stops. ie. when Im doing 30 + metre stuff. (I don't do deeper than 40 unless on a course) I think about putting in the stops..

around the 20m  I just try and keep it 5 - 9m a minute up to a 5m stop and then try 3 mins up to surface! Though I dont always manage it.


Ian
 

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Guys

What an interesting thread, Rasilon - well done on some top explenations.

Peter where did you pick up the 2/3 rule, i quite like that.

Regards

Paul
 

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<font color='#0000FF'>Hi

Relating to Gradient Factors here is an explanation by a guy on thedecostop.com

This is quite a good site for budding techie divers (whatever that means) to lurk on. Its a spinoff from scubaboard.

[b said:
Quote[/b] ]
Decoplanner Gradient Factors
Background
Since Decoplanner gradient factors are mystifying to a lot of people, I figured we would be doing everyone a service by chatting about them for the benefit of those using Decoplanner.

I'll start, and get hammered by my lack of understanding, but I figure if I had questions about them someone else might be sitting there with the same problem and not want to say anything for fear of looking stupid. We DEFINITELY want to discourage this type of behavior on this board and encourage people to speak up...nobody will make you feel like an idiot just for asking stuff (please keep this in mind when I fuck this decoplanner stuff up  ).

Anyway...gradient factors are used to adjust the dive profile giving the diver control over the conservatism and shape of his/her deco. Essential background reading is included in Decoplanner help files and also can be found here:

http://www.gue.com/dplan/docs/Deco/...%20M-values.pdf

Although we won't talk about everything here, basically touching on gradient factors (GF) and the associated pressure graph will go a long way in furthering our mutual understanding over something this cryptic. IMHO, you have to read Baker's papers 5 times each before they start to make sense, so hopefully this will save someone a couple readings..

What They Do
GF Lo% controls the depth of the first stop (deep stops)
GF Hi% controls how close the tissue compartments are allowed to reach the M value line. A 0% gradient is equal to the ambient pressure line (neither off-gassing or on-gassing). A 100% gradient is equal to the M-value line and is the furthest point into the decompression zone settable in Decoplanner.

What The Hell Does That Mean
Set GF Lo% lower to drive your initial stops deeper.
Set GF Hi% lower to increase conservatism and lengthen deco or higher to decrease conservatism and shorten deco.

What The Hell is the Graph With No Legend?
The graph with no legend is the tissue pressure graph. After reading Eric Baker's article, "Understanding M-Values", you can make sense of this graph and use it to understand what is happening as you adjust gradient factors.

From Erik's paper, you will note that the zone in between the ambient pressure line (below) and the m-value line for a specific compartment (the colors match up on the graph for each compartment - see below) is the "decompression zone". By ascending to a level that puts that compartment into the decompression zone, a positive gradient is created and the compartment will off-gas or decompress (off-gassing = decompressing).

The closer a particular compartment gets to it's M-value line, the greater the pressure gradient that is created. Obviously, the danger is that if you off-gas/decompress too quickly, you will develop DCS symptoms and symptomatic bubbling.

This gradient is controlled by GF Hi% in Decoplanner. The higher you set it (up to 100), the closer these compartments are allowed to get to their respective M-Value lines.

Summary
This whole thing was a summary of what GF Hi% and GF Lo% do and how to interpret the tissue pressure graph. I am in no way a decompression expert, but I guess you realized that since you just read this..

O
Caution should be taken in setting your lowest gradient too low as you will still be absorbing nitrogen. This will cause the computer to extend stops in the 6 mtr region. Also setting the hi gradient higher than 90% has resulted in more cases of DCI. GUE recommend 30/90 although some prefer 20/80. JPlan allows you to play with these settings and view comparisons.

Hope that Helps

WL

PS in terms of applying deep stops to your rec diving, instead of doing the 3 minutes at 5 mtrs thing, try spreading the 3 minutes between 12, 9 and 6 metres. This lessens the 'fizzy bottle' effect described earlier. Your computers might not like it though  
 

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<font color='#0000FF'>I think the fizzy drink analogy says everything you need to know, open the top of the bottle extremely slowly and it won't froth up - nuff said.

As for the gradient model stuff - that's all these things are, just models. In science, folk are always modelling this or that system or suchlike, but anyone who believes these are the same as real life biological systems won't get far.

As for what constitutes deep versus shallow stops, I think that's a bit non-specific but would suggest that it discriminates between the more typical 3m, 6m, 9m & 12m stops and those you might do on a dive to over 35m/40m.

Personally, the slower I can come up the happier I feel.

Chee-az
Steve
 

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[b said:
Quote[/b] (Paul Oliver @ May 18 2003,19:38)]Peter where did you pick up the 2/3 rule, i quite like that.
Sorry Paul, I just found the question.
 It was from the Dive Doc at Dunstaffnage pot, during my 1st chambering, so I tend to belive him more than just your average Joe-Diver on the street. I might believe him, I just wish I had listened a bit more now.

Peter
 

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Yeah peter that sounds like a very good rule of thumb, i think i will use it in future it cant do any harm, hows the no diving going, nearly ready to get in again?
 

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I'm up at Aberdeen on Mon 9th June to be poked and prodded, so with a bit of luck I'll be back in at some point next week. To tell the truth, I'm shi**ing myself incase things go pearshaped.

Peter
 

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[b said:
Quote[/b] (peter k @ June 01 2003,16:09)]I'm up at Aberdeen on Mon 9th June to be poked and prodded, so with a bit of luck I'll be back in at some point next week. To tell the truth, I'm shi**ing myself incase things go pearshaped.

Peter
good luck, whats for you, will no go past
 
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