Modern Ratio Deco usage?

[KevinNM]

yes it used to be something like -5/110 as a GF setting. Now its more like 15/100
Still nothing like 40/80

No, it's 20/85.

 

[rjack321]

No, it's 20/85.

That is the target GF for decoplanner but that's not what people actual end up doing. The pauses deeper shift the gf low smaller (but at least not negative like the 75% rule often did) and that time ends up impacting your surfacing gf highs so they are above the 85%target. Depending on the dive up to ~95% (which is better than the previous ~100+% that the old RD rules produced)

The old basis of RD was 30/85 fyi but so much time was moved around that it was not 30/85 in any way shape or form The total time matches within a minute, the shape was -5/110 ish

 

[Kevrumbo]

That is the target GF for decoplanner but that's not what people actual end up doing. The pauses deeper shift the gf low smaller (but at least not negative like the 75% rule often did) and that time ends up impacting your surfacing gf highs so they are above the 85%target. Depending on the dive up to ~95% (which is better than the previous ~100+% that the old RD rules produced)

The old basis of RD was 30/85 fyi but so much time was moved around that it was not 30/85 in any way shape or form The total time matches within a minute, the shape was -5/110 ish

The solution again in "modern Ratio Deco usage" with regard to bubble model/dual phase implementation methods like RD, and the implications of the NEDU Deep Air Deco Dives/Deepstops Study, is to pad the shallow deco stop with extra 10min O2:Air break 5min sets to effectively off-gas those slow tissues.

Granted, this may be not as efficient as alternatively "de-emphasizing" deep stops using gas content only models like Buhlmann GF's 50/80 or 40/70 on a Shearwater Petrel/Perdix Dive Computer, but if you have to choose to use RD as back-up with a Bottom Timer, the strategy of extending out the Oxygen deco stops in a RD profile is the best practical treatment to relieve the surfacing supersaturation problem of the slow tissues . . .and in my experience, especially after several consecutive days of high FN2 bottom gas Open Circuit decompression diving (i.e. Nitrox and Deep Air).

 

[Ayisha]

Worth mentioning that GUE have recently updated their ascent procedures to remove the 75% recommendation, in favour of planning deep stops more closely aligned with Buhlmann theory.

What are the new ascent procedures? Since 75% only applied to tech diving, are there changes to recreational ascent rates? Thanks.

These are from the SOP file from a couple of years ago:

Ascent Rates
The following are guides for use in calculating various ascent rates and profiles. Divers should be cautioned that the on-site environment will ultimately determine the final shape of the profile. This is a team process that all members must participate in. When feasible the last stop should be conducted at 6m/20ft followed by a slow ascent of 1m/3ft per minute to the surface.

Recreational
• Calculate 50% of the average depth of the dive
• Ascend at 9m/30ft per minute to the calculated depth
• Conduct a one minute stop for each remaining 10ft/3m interval
• One minute stops are executed as a 30 second stop and 30 seconds of movement to the next shallower interval

Tech 1
• Calculate 75% of the average depth of the dive
• Ascend at 9m/30ft per minute to the calculated depth
• Adjust ascent rate to 6m/20ft per minute thereafter until intercepting the gas switch or decompression profile which ever occurs first

Tech 2

• Less than 15 minutes bottom time:

◊ Calculate 75% of the average depth of the dive ◊ Ascend at 9m/30ft per minute to the calculated depth
◊ Calculate 50% of the average depth of the dive
◊ Adjust ascent rate to 6m/20ft per minute and ascend to the calculated depth
◊ Once this depth is reached adjust ascent rate to 3m/10ft per minute thereafter until intercepting the gas switch or decompression profile which ever occurs first

• More than 15 minutes bottom time:

◊ Calculate 75% of the average depth of the dive
◊ Ascend at 9m/30ft per minute to the calculated depth
◊ Calculate 50% of the average depth of the dive
◊ Adjust ascent rate to 3m/10ft per minute and ascend to the calculated depth

 

[huwporter]

What are the new ascent procedures? Since 75% only applied to tech diving, are there changes to recreational ascent rates? Thanks.

These are from the SOP file from a couple of years ago:

The new rules are appearing in the latest training materials, but the SOP doc hasn't been updated yet.

I don't know if recreational ascent procs are changed as well, sorry.