From 6m to Surface after Deco

[DevonDiver]

This is cool - did you come up with that approach yourself?.... Using the GF99 on the Petrel to help throttle down the ascent is a great tip.

Yeah, I don't know anyone else that uses GF99 for that purpose (except my students who also own Shearwaters).

Keeping your eye on the GF99 display during final ascent to surface is quite eye opening. That's applicable on both Tec and rec dives...

I need to remember to take a video of the display during an ascent, so that non-Shearwater divers can see what we're talking about.

 

[Kevrumbo]

It's a convenient feature to utilise on the Petrel/Perdix. For example, to compensate for several consecutive days of deco diving especially high FN2 bottom gases like Air or Nitrox, I've changed the GF99 on the Petrel from 85 to 70 or 60 during my O2 stop at 6m to extend the profile time out.

Same thing for deco compensating for cold water hypothermic conditions; change GF99 real time during the dive from 85 to 80 or 75 at the 6m O2 stop (or as long as you can stand the cold), and the Petrel/Perdix automatically recalculates the extended deco time and tracks & updates the residual inert/O2 exposure for you.

 

[kensuf]

But then you are stopping at 9m and go all the way to 4.5m meaning you are not stopping every 3 m, I can understand if you stop at 12-9-6-3. it seems a step to fast

Reading is fundamental. I never said go from 9m to 4.5m. I said "I no longer do all of my O2 time at 6m" and then outlined a strategy of splitting oxygen time into stops at 6m, 4.5m, and 3m.

Here is what I wrote:

Years ago I used to do all of my O2 time at 6m (20'). I don't do that anymore, and I don't go straight from 6m to the surface. I break my O2 time into 6m, 4.5m, 3m, and a slow ascent to the surface.

Let's say I have a deco obligation that calls for 15 minutes of oxygen time. Typically, a Buhlman schedule will break that into 5 minutes at 6m and 10 minutes at 3m. While some people may choose to do all of the 15 minutes at 6m, I will do 5 minutes at 6m, a 1 minute ascent to 4.5m (15') where I'll hold for 4 minutes, followed by a 1 minute ascent to 3m where I'll hold until clear, then a 1-2 minute ascent to the surface.

If it's a bigger exposure my final ascent from 3m to the surface will be slower.

 

[Remy B.]

Correct, my mistake.

 

[Jack Hammer]

Depends on how much deco, conditions, and my mood. O2 mostly at 20'/6m, followed by a slow ascent of 3-6 minutes to the surface while staying on O2. Then sometimes O2 while on the surface and no rush yo get out of the water.

 

[joshk]

Yeah, I don't know anyone else that uses GF99 for that purpose (except my students who also own Shearwaters).

I like to keep an eye on GF99 during an ascent to track initial stop and surfacing values. Often times the ascent is slower, and the stops longer. It's a nice way to apply some numeric value against dives where I was cold, worked hard, or otherwise feel like putting some extra time on the clock.

 

[RyanT]

When I finish my obligation at 15', I crawl to the surface. This is often pushing 2 min to go from 15' to the surface.