Deco Table comparison...

[hydro12]

Hopefully this is not interpreted as a hijack and I certainly hope it sheds some light on deco model comparison for the OP:

Joel,

In regards to your Nautilus deco software I was reading that the ZH-L16A algorithm was a purely mathematical model developed by Buhlmann and was replaced by ZH-L16B and C for the purposes of tables/software for application in real-world use because A was found not to be conservative enough, especially in the middle M-values (particularly causing skin bends, is what I read).

However, my observed use of the algorithm seems quite different. I have a friend who owns Nautilus and ran a profile of a dive to 140ft/20min on Air (no accelerated deco) w/ no GFs. He also computed a 2 hr SI and ran the exact same profile for the 2nd dive. The two profiles he came up with from the Buhlmann 16-compartment algorithm in Nautilus are:

Dive 1:
140fsw/20min
30fsw/8min
20fsw/5min
10fsw/15min

2 Hour SI

Dive 2:
140fsw/20min
30fsw/8min
20fsw/5min
10fsw/22min

When I ran the same profile through GAP, both with ZH-L16B and ZH-L16C (they don't have A in GAP) with no GFs (ok, 99/100% GFs), I got the following:

Dive 1:

140fsw/20min
30fsw/1min
30fsw/3min
10fsw/8min

2 hour SI

Dive 2:

140fsw/20min
30fsw/1min
20fsw/3min
10fsw/8min

As you can see, not only does ZH-L16A appear to produce a much more conservative set of stops than ZH-L16B or C (B & C both produced the same table), but A actually gives you a longer 10 ft stop, while B & C don't extend any of the stops (Dives 1 and 2 are identical) when using the algorithms from GAP.

Seeing as how this contradicts what I've read about the different versions of the Buhlmann algorithm, I was hoping you might be able to shed some light on the disparity between the profiles.

Thanks!

It appears you are comparing the USN tables (in TDI book) with Buhlmann Tables. The USN Tables are the absolute shortest tables around. They were designed for military application where a chamber is usually on-site. However, they are the most popular tables in the world and have an outstanding track record for working well.

Buhlmann tables are more conservative than USN and you will see more stops for a deco dive and shorter times for no-stop times.

Our company manufactures NAUTILUS DIVE PLANNER which has 5 different algorithms in it so you can compare different "tables" in a software planning mode. You can find that product at:

NAUTILUSDIVEPLANNER.COM you can also read a lot about models there as well.

IF you are taking an ADV EAN / DECO class this might be a product for you as well.

Regards,