GF LO

[rjack321]

If I have a 2 minute deco obligation, I'll stick round until my GF is lower.

Same. If I have a 2 min deco obligation I probably stay 5. If I have an 8min obligation I will usually stay 10. Up to a point I just use 5min increments rounding up: 5,10,15, 20 After about 18-20 I tend to follow the plan more than just hang around until the deco is blown off and a bit.

 

[beldridg]

Interesting comments, especially around surfacing GF on longer deco dives.

I don't have any specific logic on this other than experience, but I generally dive 50/80 and add time on the last stop depending upon the total deco time (which for me is usually related to depth given wreck diving in SoCal where you are generally doing a square profile).

On dives 150'-200' I will normally spend an extra 3 minutes after deco has cleared. On dives 200+ I'll spend an extra 5 minutes after deco has cleared. This is somewhat influenced by conditions (current, swell, fatigue, cold, etc.).

Again, no science, just adding safety margin at 53 years old diving in cold water. So, I generally end up with a SurfGF about 70-75 which I guess I could just set and not pad my last stop but I've done plenty of dives with an ending SurfGF of 80 and been fine so that is what I run.

I use the SurfGF on my Shearwater on every dive. It is brilliant.

- brett

 

[Blackcrusader]

Pretty rare atm that I do deco so my shearwater is set at 45/95.
My Deco is normally not going to be more than 5 or 10 mins. I have been on a couple of dives that were not planned deco but my dive buddy decided to do an extra few mins past NDL.

SurgGF on the shearwater is excellent as is the CNS and N2 functions.

 

[DiveTucson]

@Capt Jim Wyatt despite what my student tried to tell you at Ginnie I’m typically running a 50/75 or 50/80 -Ben

 

[beldridg]

SurgGF on the shearwater is excellent as is the CNS and N2 functions.

Agree on SurfGF.

I look at the CNS clock sometimes if I'm increasing my PO2 on long deco, but I honestly don't spend much time worrying about it.

I've been a "fair bit" beyond recommended limits as I'm sure everybody else has who does long rebreather dives. I've also exploded it by doing open circuit O2 deco on stops slightly deeper than 6m/20ft since it increases exponentially beyond 1.6. The NOAA table allows 45 minutes at 1.6 and 7 minutes at 1.65.

Just to put a point on that, 22 feet is a PO2 of 1.66 for O2 so if you are 2 feet below a 20' stop, you kill your entire CNS clock in 7 minutes.

To be clear, I'm not being cavalier about the CNS clock, but I also don't run my dives based upon it. Who knows, maybe that is heresy and it is surely way off topic from the original question on GF Low.

I'm not sure what you mean by "N2 function?" Do you mean the tissue compartment graph?

- brett

 

[beldridg]

@Capt Jim Wyatt despite what my student tried to tell you at Ginnie I’m typically running a 50/75 or 50/80 -Ben

I can vouch for that.

- brett

 

[Blackcrusader]

Agree on SurfGF.

I look at the CNS clock sometimes if I'm increasing my PO2 on long deco, but I honestly don't spend much time worrying about it.

I've been a "fair bit" beyond recommended limits as I'm sure everybody else has who does long rebreather dives. I've also exploded it by doing open circuit O2 deco on stops slightly deeper than 6m/20ft since it increases exponentially beyond 1.6. The NOAA table allows 45 minutes at 1.6 and 7 minutes at 1.65.

Just to put a point on that, 22 feet is a PO2 of 1.66 for O2 so if you are 2 feet below a 20' stop, you kill your entire CNS clock in 7 minutes.

To be clear, I'm not being cavalier about the CNS clock, but I also don't run my dives based upon it. Who knows, maybe that is heresy and it is surely way off topic from the original question on GF Low.

I'm not sure what you mean by "N2 function?" Do you mean the tissue compartment graph?

- brett

Yup N2 for the tissue graph. I do a lot of 3 - 4 dives a day but its rare to really build up PO2or CNS to truly high levels as most dives are within NDL and last 30 mins at 15m or less so not so deep multilevel diving. I often do the last 10 minutes at 5m so really slow off gassing after completing the safety stop. I like the fact the shearwater shows plus minutes after you clear the safety stop. Although one diver who had not seen a perdix thought it meant I have to do another 10 mins at safety stop and didn't realize the function. I also like the large DECO CLEAR in top right of screen when you have cleared a deco obligation. Large clear letters so you really cant miss that.

 

[rsingler]

These last few posts have been reassuring. Because while I don't have a fraction of the experience @kensuf has, the comment below seems slightly backwards. After noting that with short deco he'll pad an extra few minutes (prompting my estimate of what his actual surfacing GF99 might be), he then noted that with long deco obligations, he'll stick right with the plan:

If I have a 3 hour deco obligation, such as my last dive at the nest 2 weeks ago, I'll be happy to surface with a GF of 85.

Now I understand a reluctance to spend any more time than you have to in deco, especially on a long dive. But I don't understand why GFLo 80 with three minutes of padding (e.g, surfacing GF of 74) is desirable for short deco, but on a long dive (with even more filling of slow tissues that are not as resistant to kissing the M-factor as fast tissues might be), one not only doesn't pad, but chooses a higher GF as well?
I'm not picking on you, @kensuf . I just don't understand the logic, beyond "I feel fine". If 85 is your comfort zone, then so be it. But if something is making you wait to 74 on an easy dive, then why is 85 okay when your loading is greater? I understand a reluctance to add 30 min of deco to get to 74, but then why bother with it on a short dive?

If there's some doubt prompting you to add 3 min when it's easy, it seems like normalization of deviance to skip it when the price is higher, e.g., 30 cu ft more oxygen. Help me understand how you chose this.

And you're not alone: @rjack321 does the same thing, I think:

Up to a point I just use 5min increments rounding up: 5,10,15, 20 After about 18-20 I tend to follow the plan more than just hang around until the deco is blown off and a bit.

I don't get it.

 

[rjack321]

And you're not alone: @rjack321 does the same thing, I think:

I don't get it.

Adding 2 or 3 minutes to a 3 min "obligation" is doubling your deco for basically no effort at all.
Adding 2 or 3 mins to 4 hours of deco is not a substantive change.

I will always stay longer than required if its meaningful and helpful.

 

[Sharky1145]

I use for Air dive 80/80 on OC or CCR, and for Tx dive, my Lo GF are between 30-50 and my Hi GF are between 50-80 (depending of the profil of the dive and the mix I use).

I follow the recommandation of Bernard Gardette, a french professor who worked with the Comex.