Question about Shearwater default GF low settings

[tursiops]

Yes: it starts with 'D' and ends with 'SAT'. It's been around since 1994.
HTH

DSAT stands for Diving Science And Technology, the PADI affiliate that did the work, and it is older than 1994; that is when the report was published. 'The first RDP was issued in 1988.

By the way, if anyone wants to play with it, the current version of the RDP -- multi-level with 5ft increments in depth -- is online at .::Electronic Recreational Dive Planner - eRDPML::..

 

[inquis]

That is a good point, do we know if it [inquis: a higher integrated supersaturation] actually increases likelihood of DCS? Your phrasing sounds like you are skeptical.

ISS is an interesting tool, but easy to mis-apply. Dr. Simon Mitchell advocates for limited utility:

ISS comparisons are only useful for comparing profiles that are substantially equivalent in important respects (eg to the same depth for the same bottom time with the same total decompression time, but with different distribution of stop depths and times).

My mention of ISS in the previous message was intended to be even more limited, but I didn't make that clear. I was thinking of integrating from the start of the final ascent to some time later.

Ultimately, I believe a DCS hit is more likely when multiple tissues have supersaturations near their limits compared to only one near the limit. Much like it's easy to throw at least one tail from 3 fair coins compared to 1 fair and 2 biased coins (biased against tails).

 

[dmaziuk]

Your reply is unnecessarily flippant. Asking for data or citations isn’t an attack, so relax.

The answers to the questions you asked were in the post you were replying to: the "data to back this up" is 3 decades of actual NDL dives on PADI tables, wheels, and Oceanic computers.

I would be surprised if the number of NDL dives on ZH-L16 is close to even 1/10th of that.

 

[Miyaru]

...
I purchased a Perdix 2 in the fall of 2024, and noticed that even the lowest (low) conservativity GF (45/95) in recreational mode is still more conservative than the navy NDL tables I've used for 45 years. I also noticed that I can't seem to edit the "custom GF" parameter. My question is two fold....

1) What do I need to do in order to unlock/edit the Custom GF in rec mode, and
2) What would be appropriate GF values to closer mimic navy NDL tables?
...

Hi Jim,

I have a question for you that's for sure not answered by the Perdix manual.

How does your body manage to react in the same way to the (not so conservative) navy tables after 45 years of diving?

I want to know your secret! Every time I think I'm still 25, my body says yeah right, double that amount.

 

[diversity]

Hi Jim,

I have a question for you that's for sure not answered by the Perdix manual.

How does your body manage to react in the same way to the (not so conservative) navy tables after 45 years of diving?

I want to know your secret! Every time I think I'm still 25, my body says yeah right, double that amount.

Your's is probably the most important reply I've received. Gives me something to think about.

 

[leadduck]

Is there any data to back this up?

Are you saying that we can tolerate higher gas tensions on an NDL dive vs a deco dive? What would the difference be?

The safety stop after the NDL dive effectively reduces your surfacing GF. Hence, you pick a higher GF for NDL time calculation than for a deco dive.

 

[lostsheep]

The safety stop after the NDL dive effectively reduces your surfacing GF. Hence, you pick a higher GF for NDL time calculation than for a deco dive.

Let’s me clarify.

Would ending an NDL dive with a surfGF of 85 be equivalent risk to ending a deco dive with surfGF of 85?

sounds like the answer is no due to more total nitrogen being dissolved and slower tissues being the controlling compartment.

 

[Umuntu]

Let’s me clarify.

Would ending an NDL dive with a surfGF of 85 be equivalent risk to ending a deco dive with surfGF of 85?

sounds like the answer is no due to more total nitrogen being dissolved and slower tissues being the controlling compartment.

If you set SurfGF to 85, then your dive computer will apply that as the threshold for all tissue compartments, slow or fast, and it’s not going to matter whether the planned dive was a NDL or DECO dive. You computer will suggest a “safety stop” or a “deco stop” until your computer calculates a SurfGF at or below 85 for all abstract tissue compartments. Whether the dive was NDL or DECO being irrelevant for this calculation.

Is this too obvious ?

Or are you asking a different question ? For slower tissues, there may be higher N readings on a DECO dive compared to an NDL dive, but your dive computer will suggest stop lengths to bring all tissue groups below SurfGF.

 

[lostsheep]

My question can not be simplified anymore.

You are positing they are equivalent risk, others are taking a different stance.

I don’t know , and would like actual data but I don’t think it exists.

 

[dmaziuk]

Would ending an NDL dive with a surfGF of 85 be equivalent risk to ending a deco dive with surfGF of 85?

Not because the slower TC would be controlling -- my understanding is SurfGF is calculated from the controlling TC, -- but because the slower compartments in general will be more loaded and you would want a "better" metric that takes that into account. Like ISS for example.