Gf Starting Point

[KenGordon]

I used Multi-Deco with GF 100/100 (I don't remember if I used Buhlmann B or C) to compare dive profiles that required no stops to what the Oceanic manual said for NDLs for the same square profiles. The results were within 1 minute or so at all recreational depths.

I understand what you said, but it doesn't seem to refute my thought that diving with a GF High of 85 is more conservative than doing NDL dives on an Oceanic computer with DSAT and no CF set. The OP specified 45m or less, which is another 20' beyond what I looked at, but I'm skeptical that the results would diverge by a huge amount in that bottom 20'.

If your intention was to refute that notion, then I am not knowledgeable to draw the line from what you said to that conclusion. If that is the prooper conclusion, I would be grateful for more explanation to help me understand.

What a computer does for a no stop dive and what it does for a dive with stops are not at all the same thing. The NDL will be reached when the leading compartment gets to the over saturation limit, but if you start doing stops then other, probably slower, compartments will come into play, later those will become the limiting compartments while the fast one will have come down to ambient. You are trying to compare curves derived from a dozen or more equations with a single data point.

Just because one computer has shorter NDL times than another does not mean that when doing stops it will get you out with less deco stress.

To say that computer X is more conservative than computer Y you need to compare those equations. You may find that some compartments allow more oversaturation and some less. Then what? It starts to depend on the dive profile in question. You cannot generalise.

In particular I seem to remember reviews of the DSAT ones saying that it gave much longer stops than the VR Technologies computer using ZHL16C see A sense of algorithm

 

[rjack321]

30/70 in warm water for short exposures is already way more conservative than the old standby which was 30/85. And people would add deep stops to that (mistakenly) and sometimes shorten the shallow stops by moving time around into the old mythical "oxygen window". So 10 yrs ago it wasn't uncommon to net end up with a 5/95. Miraculously most of us were fine.

For those exposures, I would be happy bumping the GF high up to 80. I don't think the GF low is very relevant for that short a time. You can bump it up but the reality is its like 2mins moved from 60 to 40ft.

 

[Divetech99]

I did buy Multi-Deco now and I will play with it,

Note that MultiDeco on iOS has a bug. The OTU is not accumulating as it should over repetitive dives. if you're doing multi deco dives over multi days, the accumulated OTUs will only show the calculated OTUs for the first dive. Thus giving you a false reading that your OTU is low.

 

[Remy B.]

Window version

 

[DevonDiver]

I tend to start with a single deco gas of 50%, until the depth/time obligates sufficiently long shallow stops to dictate a 2nd gas (100%). When using a single deco gas of 50%, I want my stops to start at the MOD (21m/70ft). If they don't already, then I will set the GF-Lo to achieve that.

 

[Michael Guerrero]

I've been using 50/85 for a while using 50% and 100%. Not dead or bent...yet.

 

[Macan]

For the typical 50 meter dive at 25/30 minutes, I use 50% O2 as the first deco gas. First stop is at 20 meters and switch from Backgas to EAN50 Deco gas. This gives you a GF-Lo of 40%. I use 85% GF-Hi then, as conditions warrants, pad my final stop to bring my GF-Hi down to 70% or lower using the Shearwater GF99 indicator.

This nicely works out to GF 40/85 or 40/70 which is the recommendation of deco experts based on the NEDU research on deep stops.