On a NDL dive, which computers' NDLs are not affected by GFLo?

[scubadada]

Unknown but doesn't have custom GFs
Divecomputer.eu/Deep 6
Garmin Descent
Liquivision Lynx
Heinrichs Weikamp
?SeaBear (consumed by SP)

I believe all have custom GFs except the Liquivision Lynx, which has 3 presets in the tec mode. @stuartv can confirm for the Seabear H3

 

[scrane]

Even if you plan an NDL dive, isn't it worthwhile to program a moderate GF Lo in case you inadvertently fall into deco?

 

[tursiops]

Even if you plan an NDL dive, isn't it worthwhile to program a moderate GF Lo in case you inadvertently fall into deco?

Of course....but it is a separate decision that does not affect the NDL....that is the point here.

 

[stuartv]

I believe all have custom GFs except the Liquivision Lynx, which has 3 presets in the tec mode. @stuartv can confirm for the Seabear H3

The Seabear H3 does allow custom GFs. I can't remember whether the GF Lo affects the NDL or not, though. Mine died and could not be repaired. They quit making them years ago.

Even if you plan an NDL dive, isn't it worthwhile to program a moderate GF Lo in case you inadvertently fall into deco?

There is an active and valid (in my opinion) question regarding what constitutes a moderate (i.e., in my opinion, "moderately conservative") value for GF Lo.

Some people are of a mind that a low number, like GF 30, is more conservative (with regards to risk of DCS) because it results in an ascent with a deeper first stop and a longer total ascent time.

Others are of a mind that a high number, like GF 85 is actually more conservative. Those people say that it is better to get more shallow quickly. The idea being that stopping deeper has you off-gassing in your fast compartments but you're still on-gassing in your slow compartments. So, you end up doing deco for your deco, as some say. Meaning, you are spending time in a later deco stop to off-gas the inert gas that you absorbed during an earlier, deeper deco stop.

The whole subject is, obviously, very complex and there is an extent to which EVERYONE are really just blind hogs searching for acorns.

When all else fails, I always think back to a saying that I have heard attributed to John Chatterton, during the tech classes he teaches. "There is only one reason anyone ever got bent: They didn't do enough deco."

 

[dmaziuk]

Of course....but it is a separate decision that does not affect the NDL....that is the point here.

It affects your gas planning. If you plan to "inadvertently" go into deco on "moderate" GF Lo, you should have the gas to complete the more and longer deco stops. Or have a computer that "just recalculates your way to safety" after you blow a mandatory deco stop or three.

I'm sure @huwporter is right in that IRL the differences should not be large enough to matter, but computer models don't track real life. We just compute the numbers, its the scientists who tell us what numbers to plug in and WTH they all mean.

 

[scrane]

I think it's becoming clear that GF Hi is responsible for NDL limits, but I just wanted to point out that GF Lo plays a part in overall dive mechanics. I have seen people refer to GF numbers like 95/95 and was wondering if GF pairs like these have any place outside of a theoretical discussion of NDLs.

 

[stuartv]

I think it's becoming clear that GF Hi is responsible for NDL limits, but I just wanted to point out that GF Lo plays a part in overall dive mechanics. I have seen people refer to GF numbers like 95/95 and was wondering if GF pairs like these have any place outside of a theoretical discussion of NDLs.

You mean, does GF95/95 have a place in the real world? I would say it absolutely does. I know a number of tech divers who use numbers like that as their normal numbers. I'm talking about people who are regularly diving in the 200 - 300 foot range. However, it should be VERY CLEAR that there is more to their dive plan than simply setting their computer to GF95/95, doing their dive, and following their computer to the surface. I think everyone (of those serious tech divers) that dives numbers like that simply uses those numbers as a way to get shallow as quickly as they can, and then they take other steps to off-gas to a level they deem safe, for them, before they surface. (and this is not the right forum or thread to get into the details of that, even if I really knew them all)

 

[dmaziuk]

I have seen people refer to GF numbers like 95/95 and was wondering if GF pairs like these have any place outside of a theoretical discussion of NDLs.

Discussing the place of GF pairs in calculation of NDL is akin to discussing which end of a crowbar is better for hammering screws.

 

[KenGordon]

You mean, does GF95/95 have a place in the real world? I would say it absolutely does. I know a number of tech divers who use numbers like that as their normal numbers. I'm talking about people who are regularly diving in the 200 - 300 foot range. However, it should be VERY CLEAR that there is more to their dive plan than simply setting their computer to GF95/95, doing their dive, and following their computer to the surface. I think everyone (of those serious tech divers) that dives numbers like that simply uses those numbers as a way to get shallow as quickly as they can, and then they take other steps to off-gas to a level they deem safe, for them, before they surface. (and this is not the right forum or thread to get into the details of that, even if I really knew them all)

Is that the kind of people who do two such dives and then a third to lift the anchor?

 

[Jay]

I believe all have custom GFs except the Liquivision Lynx, which has 3 presets in the tec mode. @stuartv can confirm for the Seabear H3

Thanks - I've amended my earlier post.

Hi @Jay_Antipodean Maybe folks that have these other computers will take the time to check the planner for 10/90 vs. 90/90, or some other easy comparison to see if GF low affects NDL

I'll send some PMs/a few new threads to try and get more results in the door.