Your Gradient Factors?

[nadwidny]

You mean I need to include DIR/GUE/UTD as part of the broader world of recreational diving?

Actually no, that's not what I meant. But the tangent it sent you on was amusing.

 

[elmo]

You mean I need to include DIR/GUE/UTD as part of the broader world of recreational diving? Naw. They are outliers, a tiny fraction of the global diving activity.

My view of tables and actual depth comes from pre-computer days diving in Chicago, New England, Europe, using many kinds of tables. ALL of which clearly specify actual depth, not some sort of average depth.

One example above talked about going between 220 ft and 240 ft and calling it 230 ft. OK, that is what is called a tangent linear approximation, perfectly plausible for gas up take. But that is not the average depth of the dive, just of a little segment of it. That appears to be what the Ratio Deco folks have reinvented, the tangent-linear approximation. No magic, but definitely not the average depth of a dive, just of some segment of the dive.

The examples above that are trying to justify their position are really way off in the corner of recreational diving: trimix, 240 ft, 4h dives, O2 switch and deco, etc. Does the Navy dive manual or the NOAA diving manual or DCIEM or BSAC or anybody in the mainstream use average depth with a table?

I can't speak for anybody else, but I am not asking you to buy into anything DIR, Ratio Deco, or anything beyond school-level maths.
Let's assume you have some method to plan a no-decompression multi-level dive. It could be the PADI eRDP-ML, Wheel, or another organization's equivalent. Or it could be recreational dive planner software (e.g. Subsurface in Recreational planner mode), a phone app, or it might be built into your dive computer. Could you please humour me for a moment?
A) Plan a non-decompression dive with a square profile (e.g. all the bottom time spent at 100 ft) - no trimix, nothing beyond recreational limits - to determine your NDL for a particular depth
B) Plan a multi-level dive with the same average depth that would be allowed by the PADI eRDP-ML (deep-to-shallow - as I'm sure you learnt at some point), with the same average depth (e.g. first half of bottom time at 120 ft, second half of bottom time at 80 ft)

Can you say which plan gave you a longer NDL? I am willing to bet it was plan B. So, it you were planning a deep-to-shallow multi-level dive but planned for the NDL based on average depth using tables intended for a square profile, you would be on the safe side. Try it again - can you come up with a deep-to-shallow profile where that isn't true?

When planning a deep-to-shallow profile dive, it is not unreasonable to use the average bottom depth to calculate the NDL from a dive table. There are difficulties (e.g. how good are you at tracking your average depth during a dive) and by no means do you need to use it if you don't want to, but it isn't bogus, and it isn't a cult philosophy.

 

[100days-a-year]

Can we get back to the topic of bungied wings, independent doubles, deep air or whatever the nominal topic was

 

[tursiops]

it is not unreasonable to use the average bottom depth to calculate the NDL from a dive table

This misses the point entirely. We are not talking about the averate bottom depth, but rather the average dive depth.
Simple example using air, calculated on a PADI eRDPML.
100 ft, NDL, 20 mins, but ascend at 15 mins to 40 ft; new NDL is 83 minutes, but stay only 80 minutes. Nice 95-minute dive, plus some ascent time and a SS.
The average depth of that dive is 50 ft ((100x15 + 40x80) /95). A single dive to 50 ft has an NDL of 80 minutes.
You cannot validly plan or execute that two-level dive using average depth.

 

[Ayisha]

Can we get back to the topic of bungied wings, independent doubles, deep air or whatever the nominal topic was

Haha, except that the topic, gradient factors, ties in with average depth because GF Lo and the percentage used of average depth both determine the first stop of a dive.

So for some agencies, GF's and average depth are entwined.

 

[tursiops]

Haha, except that the topic, gradient factors, ties in with average depth because GF Lo and the percentage used of average depth both determine the first stop of a dive.

So for some agencies, GF's and average depth are entwined.

For one agency, perhaps.

 

[CAPTAIN SINBAD]

For one agency, perhaps.

Three!

 

[CAPTAIN SINBAD]

This misses the point entirely. We are not talking about the averate bottom depth, but rather the average dive depth.
Simple example using air, calculated on a PADI eRDPML.
100 ft, NDL, 20 mins, but ascend at 15 mins to 40 ft; new NDL is 83 minutes, but stay only 80 minutes. Nice 95-minute dive, plus some ascent time and a SS.
The average depth of that dive is 50 ft ((100x15 + 40x80) /95). A single dive to 50 ft has an NDL of 80 minutes.
You cannot validly plan or execute that two-level dive using average depth.

Which gradient factor is this? I am unaware of PADI or DSAT but Minimum Decompression Limits tend to fall into Buhlman 30/70 ish.

 

[tursiops]

Three!

Names?

 

[CAPTAIN SINBAD]

GUE, UTD and ISE. All three DIR agencies.