Decompression Planning

[DRE]

"DRE, thanks for your reply. The software is used is Voyager 2000, from DiveRite. The stops can custom set if you like. The default stops are every 10ft feet. The only change I made to the default was to make the last stop at 15ft, instead of 10ft."

I would even recommend making your last stop 20ft instead of 15ft, and then to go from 20 ft to the surface in about 3 minutes time. From 20ft to the surface is one of the more critical parts of the deco (although you are "cleared" according to the software) as any residual inert gas will escape in bubble form. If you go too fast, these bubbles will trap and cause a very mild form of DCS, ie post dive fatigue, etc. Going up really slowly makes sure you get rid of these last bubbles.

"In your reply you also indicated that you would make 10second stops starting at 80% of the max dive depth. Would these stop be every 10ft ? And if so, wouldn't slowing your ascent to your first stop accomplish the same thing ?"

The 10 seconds every 10 ft makes sure your ascent isn't too fast. It basically accomplishes just that. Make sure your ascent isn't any faster than 30ft/minute.

"I ran the profile again, using 1minute stops starting at 60ft, then agian at 50,40,30. The first "stop" was at 20ft, and required only one minute. The last stop at 15ft was for 22 minutes. Total dive time was 63 minutes. The dive time didn't really change, nor did the final gas usage."

Actual deco time will not decrease the way I suggested to run the deco, but it will give you a much cleaner, more optimal deco. See if you can play with the gradient factor settings of the software - I still think the profile gives you your stops too shallow, and should instead lengthen some of the deeper stops. Playing with the conservatism of the gradient factors might allow you just to do so. The problem is that most software that's out there runs straight Buhlmann models (as do all computers), which will pull you as close to the surface as possible. However, recent studies have shown that no matter what the dive, bubbles will always be present in nuclei form. Therefore it is very important to start doing deep stops in order to keep these bubbles small. Variable Permeability Models do calculate deco from a bubble instead of a tissue group perspective, but very little software is available to take that into account. It is however possible to play with the conservatism settings of Buhlmann models to approach the VPM models.
In essence good deco means a balancing act between taking advantage of the oxygen window (creating the highest possible gradient, ie Buhlmann model) and to offgas in bubble form (VPM based) without letting the bubbles get too big so they cause DCS.