olstykke:
What are the differences in the dive algorythms?
A quick and dirty history of deco...
Many tables are derivatives of Haldane's models used as the basis for the original Royal Navy and US Navy dive tables around 1910. The original model had some serious flaws but these have been largely corrected over time based on a large accumulation of operational data. The Navy has also developed new tables based on statistical rates of DCI based on the experiences of US Navy divers. The potential problem with these tables and some of the tables derived from them is that they were not really designed for repetitive multiday diving and the way they are used operationally by the US Navy differs from how sport divers would normally use them.
The University of Wisconsin developed the Huggins tables in the mid 80's based on doppler ultra sound research that indicated small asymptomatic bubble formed well within the NDL's on US Navy tables. The resulting table followed the basic USN format but with shorter no deco limits to keep divers bubble free.
Professor Albert Buehlmann developed tables beginning in the 1960's using the same basic idea but with more mathematical tissue compartments (12) including some with much longer half times. He has also developed tables for altitude diving and his ZHL-16 model is widely used in many computers. His tables are generally much more conservative than US Navy tables.
These tables have more recently been modified by by others using bubble Gradient Factors and incorporating slower ascents and deep stops which makes them more conservative. This adaptation is used in some software applications including GUE's DecoPlanner and DPlan.
The RGBM (Reduced Gradient Bubble Model) is a similar approach but using a Haldane model embedded with gradient factors and other limits on reverse profiles, and repetitive multi-day diving. RGBM is used in GAP deco planning software and recreationally adapted RGBM applications are used in several dive computers. The downside of the computer based models is that it is not very permissive on multi-day dive trips, but it is conservative. And if you read the fine print on many non RGBM dive computers, you will usually find a disclaimer indicating they are not intended for repetitive dives over multiple days. So RGBM computers are perhaps overly conservative, but they are at least designed for the average rec diver doing week long tropical dive trips.
Since about 1980 there has been research and continuing development of the Variable Permeability Model which like the GF and the RGBM approachs, produces profiles with slower ascent rates, and deep and short deco stops combined with shorter shallow stops compared to a Haldane/US Navy profile.
The basic idea behind GF, RGBM and VPM models is that off gassing occurs faster before bubbles form so that the use of shorter deeper stops is more effective in eliminating nitrogen than the "bend and treat" Haldane appproach of doing longer and shorter stops after bubble formation has occured in the tissues.
In the last 10-15 years, the use of accellerated deco as become very common. In this approach decompression gases with comparatively high percentages of oxygen (50%, 80% and 100% are common deco mixes) are used to increase the rate of inert gas elimination. The result is shorter and cleaner decompresison. Both gradient and VPM tables and software allow for this option.
Personally, I feel a lot better after doing deco on a Gradient Factor or VPM profile than I ever did on any Haldane table.
And for decon diving. How does one get into it? I'm not planning to do it, but maybe you all have some resources I might investigate into this question.
Technically oriented training agencies (TDI, IANTD, GUE, etc) offer decompression procedures courses. I think advanced nitrox and deco procedures courses are worth taking even if you never do deco diving as you will learn a lot about deco theory. Similarly, playing around with some of the deco software out there can give you a feel for how the theories work and can give you an intuitive sense of how to improve and add a safety margin to your nitorgen elimination even on recreational dives within the NDL's.