Re: NDL's

Outer Bamnks diving on the Great Escape Southern California Live-Aboard Dive Boat

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Posted by Kendall Raine on July 20, 2001 at 12:26:06:

In Reply to: Re: NDL's posted by Steve on July 20, 2001 at 11:01:23:


Why compare anything to the Navy tables? Are we still in the 60's? Do you ascend at 60 fpm? The total NDL is the wrong number to focus on. Look, every dive is a decompression dive, whether you have a required stop or not. The key is the ascent rate, or shape of the deco, not the NDL per se. As a result, total NDL is a poor proxy for "aggressive" or "conservative." Haldanean computers-almost all of them-use the same dissolved gas approach. That's one reason why computers are sub-optimal. These models generally skip the deep stops (aka slower ascent rate) for a longer stop at the shallow depths. This is otherwise known as bend'em deep and fix'em shallow-remember Bennett's article in Alert Diver "Putting on the Brakes?" These errors compound with repetative dives. I can show you Doppler results on dives where the total deco time was less and the post dive bubbling was less because of the shape of the deco was better i.e. based on a bubble model. Haldanean/Buhlman models don't establish this shape. Only bubble models do that. Comparing anything to the Navy tables is an example of "garbage in garbage out." While this problem becomes bigger the deeper you dive and longer you stay, the concept holds across the spectrum of dives.

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