Subsurface and Aladin GF's

[KeithG]

Question: Anyone have any idea or opinions on how to configure Subsurface to mimic an Uwatec Aladin?

I have loaded a cornucopia of dive profiles from my Palm Pilot into Subsurface (I can provide lots of additional background info if any one really cares). But the NDLs displayed by Subsurface do not match my dive computer.

All I want is to for Subsurface to provide non-deco NDLs "reasonably" close to my circa 1995 dive computer.

The default Subsurface Bulhmann GFs of 30/75 appear to be more conservative than my dive computer. I do realize that Subsurface runs a slightly different version of Bulhmann as compared to the early Uwatec ZHL-8.

I did find a random post via my phone Google-fu this afternoon that implied a GFhigh of around 95 for the early Uwatec Aladins.

Does anyone have any insight?

 

[atdotde]

I guess nobody outside Uwatec really knows what they put inside these grey bricks at the time. But my guess would be that GFhigh a bit less than 100 and GFlow only slightly lower than that is a good starting point for experiments. What you could do in Subsurface is to open one Aladin dive that you know was close the the NDL with "Edit in planner" and then play with the gradient factors that the ceiling matches with the dive profile.

 

[KeithG]

I guess nobody outside Uwatec really knows what they put inside these grey bricks at the time. But my guess would be that GFhigh a bit less than 100 and GFlow only slightly lower than that is a good starting point for experiments. What you could do in Subsurface is to open one Aladin dive that you know was close the the NDL with "Edit in planner" and then play with the gradient factors that the ceiling matches with the dive profile.

Agreed. I was just wondering if anyone had already done this?

The biggest hurdle is that all of our dives are multi level so the smallest NDL is generally before the mid dive point. During the second half of a dive the computer is generally giving unlimited NDL time of 99.

One approach I considered was going back to one of our LOB trips and start with a small GFhigh and then keep increasing it until there is no deco obligation. That would establish a "minimum" GFhigh since we never get deco obligations. This minimum GFhigh would be more conservative than the actual computer is.

This may be an excercise that will have to wait until I am back in the water again. Or is could pop a computer into a pressure chamber and do a few dives in my kitchen...

But I am lazy and wanted to see if anyone already had done this.

 

[KeithG]

My best guess is a GFhigh of about 90.

I popped 3 different models of Aladin (Sport, Pro, Ultra) into a pressure chamber and took them on 2 dives. I randomly recorded the NDL data at multiple points during the "dive". Note that all three computers gave very close behaviour. At several points in each dive I pushed the computers within 10 minutes of NDL (seesaw profile) so that I would have multiple visible data points to compare.

I transferred the log file from one of the computers into subsurface and fiddled with the GFhigh until I got NDLs that "closely" matched the recorded data.I started with 95 and then tried 90 and that seemed to be close enough. GFhigh might be 89 or 91?

 

[elmo]

Erik Baker published his papers "Understanding M values" and "Clearing up confusion about Deep Stops" in 1998. Before that I don't think gradient factors were used. Richard Pyle published "The importance of deep safety stops" in 1996, which popularized deep stops. Bubble models existed earlier but weren't widely used.
I doubt any dive computer using a Buhlmann-derived algorithm differentiated between conservatism at some depth (~gf low) vs conservatism on surfacing (~gf high), so while other methods of adding conservatism existed (e.g. pretend dive is deeper or longer than actual, or pretend it's at elevation) I suggest trying all gf matching in Subsurface with both gradient factors equal. In any case, differentiating between the two has a minor impact for no deco dives.
The difference between 8 and 16 tissues should be negligible for no deco dives of usual recreational duration.
My guess for best match? Gf 100/100. If not that, then something no more conservative than gf85/85.

 

[KeithG]

Erik Baker published his papers "Understanding M values" and "Clearing up confusion about Deep Stops" in 1998. Before that I don't think gradient factors were used. Richard Pyle published "The importance of deep safety stops" in 1996, which popularized deep stops. Bubble models existed earlier but weren't widely used.
I doubt any dive computer using a Buhlmann-derived algorithm differentiated between conservatism at some depth (~gf low) vs conservatism on surfacing (~gf high), so while other methods of adding conservatism existed (e.g. pretend dive is deeper or longer than actual, or pretend it's at elevation) I suggest trying all gf matching in Subsurface with both gradient factors equal. In any case, differentiating between the two has a minor impact for no deco dives.
The difference between 8 and 16 tissues should be negligible for no deco dives of usual recreational duration.
My guess for best match? Gf 100/100. If not that, then something no more conservative than gf85/85.

Thanks for the input. GF 30/90 seems a good match for my computers.

Based upon my limited knowledge of deco diving I left the GFlow at the Subsurface default of 30 since we are warm water rec divers and do not deco dive. I will have to look into the side effects of doing this?

I did try to make my kitchen dives "remarkable and aggressive". The idea was to have a series of extreme low NDL points that I could later find in Subsurface. I recognized that any time shallower than 30 feet on non-deco recreational dive would not provide usable metrics. My computer reads 99, Subsurface displays >2hrs. So I pumped the chamber up at multiple points during the dive to have the computers dip down to very short NDLs. One of the "features" of my chamber is that it leaks a bit. So I can pump it up (down?) and walk away and have the computer slowly approach the surface.

I found this page as I was trying to learn about GF's: Gradient Factors | Dive Rite It was very helpful to a noob like me.