FWIW I'm diving with 99/99 for GF. My SurfGF is usually in the 50's, sometimes 60's, seldom in the 70's. Which mean's I am diving a reverse GF*. In practical terms it's probably averaging 80/55. I tend to take it very easy from 10m and shallower, and super-slow from my 6m SS (5 min) to the surface. On deeper squarish dives to ~40m, gas isn't an issue, so as long as I achieve my SurfGF I'm not too worried about seeing NDL=0. It's dives with a shallower average depth that I need to check I've got enough gas to get my SurfGF down even though NDL is farther from the limit; with 50bar reserve, my NDL and gas limits intersect at an average depth of 16m on GFHi of 99 (SAC is 1bar/min for AL80).
I wanted to somehow assess the wisdom of this seemingly aggressive GFHi and for the occasional dives where NDL get's pushed below 5min remaining. Here's my thought process:
At max Rec depths (or slightly beyond) on Air, a 40m dive for 20min produces stops from 9m for GFLo's between 60-83 with 24-27mins of deco using a GFHi of 70. GFLo83+ is 6m stop depth.
Reducing the deco time to something closer to 'light' deco, say a 40m dive for 15mins, with a GFHi of 70, a GFLo of 65+ results in 12min of total deco starting at 6m. With a GFHi of 60, 6m stops are produced from GFLo of 70+
Given GLo has less of an effect on the depth of the first stop as max depth becomes shallower, at 30m for 25min produces 15mins of deco starting from 6m for GFLo 53+
To me, this reinforces SurfGF targeting, long SS and super slow ascent as per
Recreational Ascent Rate in the last 15 feet
That in turn (perhaps) defocuses NDL at depth ... because:
The difference between GFHi of 90 & 99 is 3 mins at 30m, 2min at 40m. Between GFHi 80 & 99 it's 6 and 3mins respectively. i.e. not massive differences at depth and it's just a question of gas supply and time availability at/near SS depths. Secondly there's seems almost/no difference between doing what I'm doing and say very 'light-deco' on a lower GFHi and a higher GFLo provided I'm slow from 10m and shallower.
re Reverse GFs: *The question of whether the actual (self adjusted) m_value line I'm following is a reverse hockey-stick (like merely padding the SS), or is a modified linear mayn't be too relevant for Rec depths.
(p.s. I realise/agree on a NDL dive GFLo plays no effective role).
Thoughts? Holes in my logic? and who else dives a similar NDL/SurfGF style?
