Unified Team Diving

1st Deep Stop: 80% of Max Depth in ATA, or Minus 2ATA Delta of Max Depth?

The criticism of the 80% rule by Rossh and others (link)-- ". . .The first stop distance for the Ratio Deco 80% method, when used on dives of 60m/200ft or less, will produce the deepest of all first stop depths. This method does not have any benefit over those at 2 ATA [delta minus the maximum depth] . . .The x% rule was originally designed for use with 270 to 300ft dives at WKPP but needs a correction to remain in context with any other depth. The efforts to extrapolate the rule base from the 300 ft dives to all other depths, have failed to address the change in scale required. "

The gist of this critique is that you're still loading bottom mix inerts at a 80% of max depth deep stop disproportionately for dives less than 60m/200'. (Actually in practice, I'm not doing a "hard" deep stop per se starting at 80% max depth for dives in the 45m/150' to 60m/200' range for 25min BT or less: only a slight 5-10 second pause to arrest the 9m/min [30'/min] ascent from the bottom).

What's the correct interpretation (or reconciliation) between the two deep stop methods?

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Reality is no one really knows what is "Right" or "Wrong" as they are all only theoretical models. The approach was developed as a combination of using a model to predict the First Stop Depth (In other words when the first compartment starts to off load) and then based on real world diving and experience. We tweaked it to fit the Ratio Deco Strategy as we do not use Max depth we use average.

So let's state this correctly...

75% of Depth based on Average Depth or if you are currently deeper than average depth, then use that depth.

So, first of all I don't do max depth and secondly we find that we are really just creating a slower ascent rate than 33'/10m per min and only starting to do true "hard" stops or extended time stops when we reach 50% of depth or Bottom time getting extended out to 30 + min

Hope that makes sense

Alright, a semantic correction -->75% of the initial Planned Depth in feet or meters; the actual value used being 75% of the real Average Depth during the dive itself.

I compromised with a Dive Buddy during my just completed Truk Lagoon trip: he ran Decoplanner 3 at GF's 10/80 to give a deep stop 2ATA delta up over the planned operational depth of 54m for 25min, Air bottom mix. Deep Stop was 1min starting at 33m and all the way to the eanx50 switch at 21m. Per Ratio Deco and the Wkpp Deep Stop Table, I wanted to do a "pauses" starting first at 39m & then every 3m up to 30m, and then 2min hard stops at 27m and 24m (ie. the secondary Deep Stop at 50% of Planned Depth) before the eanx50 switch. We ended up agreeing to a slowing 5-6m/min ascent from 54m to the stops starting at 33m.

Of the three wreck dives using this deep stop profile, one was right at planned depth of 54m for 25min (San Francisco Maru); another was a shallower average than planned depth of 54m for 25min ( 50m on the Aikoku Maru); and the last was a little deeper than planned depth ( 55m on the Oite Destroyer and we called the dive at the 22min mark). . .
What was your backgas?
kevrumbo said:
"Air bottom mix"

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