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Dave You would probably be best to send these questions to the Decoplan mail list decoplan@gu*.co* <mailto:decoplan@gu*.co*> . I hope you don't object to my cross posting of my reply. >JJ refers to figures such as 10-30, 40-60 etc. In GAP the gradient >factors are in terms of decimals (between 0 and 1.0). Is there a simple >relationship between these figures (such as a factor of 100) eg 0.2 on GAP >is equivalent to 20 on decoplanner? So when JJ recommends starting with 30 >low and 80 high can this be translated to 0.3 low and 0.8 high on GAP? The GFs are percentages, so 30 on Decoplan is a GF of 30% and is the same as 0.30 on GAP. >Another question, while I am at it. Setting the low gradient factor to a >smaller number (eg 0.1 on GAP) gives deeper stops, but I presume that even >the deepest of stops given on these programs is still in the theoretical >"deco zone"? Yes, this is correct. One consideration you should be aware of is that if you *plan* a square profile dive but *execute* a multi level profile, you would find that the first stop would be shallower had the deco software been aware of your multi-level dive. In this case, were you to run a GFLo as low as 10%, there is a chance that your controlling tissue could be on gassing as a result on the first stop executed. In this case, I would run a shorter table or use some common sense and skip some of the deeper stops, depending on my multi-level profile. > Judging by the quick example I worked out last night for a 50m >dive 0.1 gave the deepest stop at around the same point as the 'Pyle' >method. Would this be generally true, or are some people thinking that >'Pyle' stops may be a little too deep? What works, works. One difference between Decoplan stops with a low GFLo and Pyle stops, is that Pyle stops do not run in 3m/10' increments as do Decoplan stops. If you think about this, it means that Decoplan stops will generate a smoother curve, thereby resulting is smaller variations in tissue over pressurisation. Since this is one of the objectives of deep stops, I would sooner go with a GF approach. Your point about whether a 10% GFLo equating to a Pyle first stop, and whether it is too deep is difficult to answer, since it depends on what *you* the diver want to do. However, consider my point about the lack of 3m stops in the Pyle approach. All that is happening is that Decoplan is operating on a greater level of granularity. If Decoplan were to operate with stops every 9m/30', then you would see the first stop for Decoplan arriving deeper than before (unless it happened to be on the same 9m boundary) and the amount of time required at each stop to increase and look more like Pyle stops for the deeper stops. The greater the granularity, the smoother the curve, and the shorter each stop. The result is closer to the "ideal" curve and specifically the "ideal" first stop depth, whatever that is. > Also why choose (ie what >advantages/disadvantages in choosing) the deep stops to start shallower if >you can do deeper stops that are still in the "deco zone"? My old model for stops was one of having mandatory stops and deep stops. I considered these to be in some way different. The mandatory stops were those that a piece of deco software told me about, the deeps stops were ones I decided to execute. I *believed* in the deco software and *liked* the deep stop approach. However, the more I learnt, the less I believed in the deco software with all of the padding and fudge factors. Progressively, and we are taking a couple of years, I came to *believing* the deep stop approach and *doubting* the mandatory stops. This was symptomatic a lack of clear thinking on my part exacerbated by not having any deco software that would allow me to properly plan deep stops. The GF approach has unified my thinking in respect of stops - now I use Decoplan, there is no such thing as a deep stop. They are all stops and part of the same deco curve. So, on to your question, you choose your tissue over-pressurisation, based on what you consider sensible. I do not vary GFLo for my tables from one dive to the next. I stick with what I use. The advantage with stops that are only just in the deco zone is that the tissue over-pressurisation is minimal. The disadvantage is that there is no significant tissue vs. ambient gradient to facilitate off gassing. Move the first stops higher and you'll create a higher tissue over-pressurisation - a bad thing bubble-wise but a good thing for off gassing due to the higher gradient. (I have not mentioned switching to other gasses, as this is a separate discussion.) At the end of the day it is a compromise between reward and risk. You could run a 10% GF all the way to the surface and get out clean and a brand new pin, but you'd be underwater for some time. Equally, you could run straight Buhlmann with 100% all the way and get out really quick but the chances are that you would be bent as a pretzel. The best answer overall is to stick with the recommendations of JJ WRT GFs, and find out what others do and very carefully and progressively experiment to see what works for you. David Shimell Email: shimell@se*.co* <mailto:shimell@se*.co*> Project Manager, IBM NUMA-Q, Sequent Computer Systems Limited, Weybridge Business Park, Addlestone Road, Weybridge, Surrey, KT15 2UF, UK registered in England and Wales under company number: 1999363, registered office as above -----Original Message----- From: David Reinhard [SMTP:reinhard@oc*.co*.au*] Sent: Friday, January 21, 2000 8:32 PM To: techdiver@aquanaut.com Subject: gradient factors I have just been catching up with some of the interesting material in the "Sample Deco Dive - 220 for 25" thread (I've been busy so haven't read it all yet). I haven't yet seen the Decoplanner software but what i am wondering is how the gradient factors in that program relate to those in 'GAP'. JJ refers to figures such as 10-30, 40-60 etc. In GAP the gradient factors are in terms of decimals (between 0 and 1.0). Is there a simple relationship between these figures (such as a factor of 100) eg 0.2 on GAP is equivalent to 20 on decoplanner? So when JJ recommends starting with 30 low and 80 high can this be translated to 0.3 low and 0.8 high on GAP? Forgive me if this is a stupid question, or I have got it entirely wrong, but the gradient factors concept is new to me. Another question, while I am at it. Setting the low gradient factor to a smaller number (eg 0.1 on GAP) gives deeper stops, but I presume that even the deepest of stops given on these programs is still in the theoretical "deco zone"? Judging by the quick example I worked out last night for a 50m dive 0.1 gave the deepest stop at around the same point as the 'Pyle' method. Would this be generally true, or are some people thinking that 'Pyle' stops may be a little too deep? Also why choose (ie what advantages/disadvantages in choosing) the deep stops to start shallower if you can do deeper stops that are still in the "deco zone"? Thanks for any advice, Dave. -=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=-=- Ocean Internet - "The Quality ISP" http://www.ocean.com.au/info.html -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'. -- Send mail for the `techdiver' mailing list to `techdiver@aquanaut.com'. Send subscribe/unsubscribe requests to `techdiver-request@aquanaut.com'.
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