Garmin fenix 8 NDL

[Amsterdam2001]

Hello, I bought a Garmin Fenix 8 a couple of weeks ago and dived with it this week. I noticed that my NDL was very low compared to the other divers that where using other computers like suuntos and shearwaters (10 minutes lower at conservatism normal). I then checked in the dive planner to see what my ndl would be at 25 meters in normal conservatism after a couple of days of surface interval. It gives me 18 minutes. The PADI dive tables indicate a 29 minute ndl at 25 m. Even at low conservatism the Garmin indicates 23 minutes ndl. Does anyone know what might cause this?

 

[scubadada]

Hello, I bought a Garmin Fenix 8 a couple of weeks ago and dived with it this week. I noticed that my NDL was very low compared to the other divers that where using other computers like suuntos and shearwaters (10 minutes lower at conservatism normal). I then checked in the dive planner to see what my ndl would be at 25 meters in normal conservatism after a couple of days of surface interval. It gives me 18 minutes. The PADI dive tables indicate a 29 minute ndl at 25 m. Even at low conservatism the Garmin indicates 23 minutes ndl. Does anyone know what might cause this?

The owner's manual is not what one would expect for a dive computer. The computer appears to run Buhlmann ZH-L16C. How is conservatism set, presets with what GFs, custom GFs? Where can I find this in the owner's manual?

 

[Nick_Radov]

You might want to move this question to the Computers, Gauges, Watches & Analyzers forum regarding specific settings or differences between devices. As for the NDL, that will be the same as any other device using the Bühlmann ZHL-16c algorithm with the same conservatism Gradient Factor (GF) settings. If you want to understand gradient factors that has been extensively discussed in the Decompression Theory forum. I wouldn't recommend changing the defaults unless you're sure you know what you're doing.

 

[scubadada]

You might want to move this question to the Computers, Gauges, Watches & Analyzers forum regarding specific settings or differences between devices. As for the NDL, that will be the same as any other device using the Bühlmann ZHL-16c algorithm with the same conservatism Gradient Factor (GF) settings. If you want to understand gradient factors that has been extensively discussed in the Decompression Theory forum. I wouldn't recommend changing the defaults unless you're sure you know what you're doing.

Good idea, done. I did not notice the forum, only the content.

 

[inquis]

The PADI tables are quite liberal by today's standards (equivalent to a gradient factor of about 95 for a clean dive).

 

[tursiops]

A number of Google entries say the Fenix 8 dive settings have adjustable Gradient Factors, but I cannot find anything in the manual about that.
My guess is the OP is on a high conservatism setting.
For example, MultiDeco suggests NDLs for air at 25m as 26 mins for GFHi=96; 22 mins for GFHi=85; and 15 mins for GFHi=70.
On some computers, Low, Moderate, and High Conservatism correspond to GFHi = 95, 85, and 70 respectively.

 

[Nick_Radov]

On some computers, Low, Moderate, and High Conservatism correspond to GFHi = 95, 85, and 70 respectively.

I don't have a Fenix 8 but other Garmin dive computers have the following conservatism settings (or you can pick any custom settings you like). The Fenix 8 may be similar.

Conservatism​	Low GF %​	High GF %​
High	35​	75​
Medium	40​	85​
Low	45​	95​

There is a debate about whether reducing the Low GF % is really more "conservative". But that's a topic for another forum, and mainly only applicable to dives beyond the NDL.

 

[Amsterdam2001]

Thanks for all the reply’s. Indeed you can choose from three conservatism settings, being high 35/75, medium 40/85 and low 45/95. What I understand from some off the reply’s is that it is just the algorithm. So others using the bühllmann algorithm also have 18 minutes ndl at 25 meters with gf 40/85? Than how could the difference be so large with my dive guide who used a suunto? At the end of the dive he had 10 minutes left while I was at 1 minute ndl (on conservatism medium) so we needed to ascend.

 

[Belzelbub]

Than how could the difference be so large with my dive guide who used a suunto? At the end of the dive he had 10 minutes left while I was at 1 minute ndl (on conservatism medium) so we needed to ascend.

Were you diving air? Are you sure the DM was as well? On air, with GFHi of 85, 18 minutes seems about right at that depth. And it will depend on the Suunto. Some newer Suunto run Buhlmann, while most run an RGBM variant. Generally the RGBMs can be more liberal on the 1st dive, but get more conservative on subsequent dives.

 

[scubadada]

Hi @Amsterdam2001

I ran a first clean dive on air using 40/85 on my Shearwater Teric NDL planner:

Your 18 min at 25 m looks to be close to what I found. Perhaps you can run your planner over the full range of depths and see how it compares to this table. Let us know how this works out.

Without knowing what Suunto computer your guide was diving and how it was set, it is difficult to compare your NDL to his. @Belzelbub made some important points. Suunto computers run a couple of versions of RGBM, one can be set to run quite liberally and the other is generally reasonably liberal on a first clean dive before becoming more conservative on repetitive dives. In addition, some Suunto computers now run Buhlmann.