Shearwater OC Rec on Low vs DSAT computers

[travlbum]

There are a million and a half threads about the Shearwater Perdix but they usually only touch on OC Rec's NDLs in low mode compared to dive computers that just use the DSAT.

So, within normal no-deco recreational limits, how do bottom times for repetitive dives compare between DSAT computers like Oceanic and a Shearwater set to OC Rec Low (45/95)?

Does anyone have a definitive answer? Or did I miss the thread that goes over this in detail?

 

[rongoodman]

It's not clear what the question is? Are you asking for comparisons between various Buhlmann GF settings and the DSAT algorithm?

 

[scubadada]

Hi @travlbum

It takes a high GF hi to closely match DSAT. Of the rec mode settings, low conservatism, 45/95, is the best fit. Either of the other two settings would be more, and considerately more, conservative.

In reality, it is a bit more complicated. I have been diving with an Oceanic VT3 and a Dive Rite Nitek Q for about the last 80 dives to gain experience with GFs. At deeper depths a higher GF hi is required than at shallower depths. I am still experimenting with GF hi of 90-100, though I have it pretty well worked out. I believe this is the case because the M-value lines probably have different slopes, with Buhlmann having a shallower slope than DSAT. The surfacing M values (Mo) for the two algorithms are pretty similar. The M value line slopes (deltaM) are available for Buhlmann, but I have not been able to find them for DSAT, a proprietary algorithm. If anyone has this information, I would love to hear about it to see if my hypothesis is correct or not

Good diving, Craig

 

[travlbum]

It's not clear what the question is? Are you asking for comparisons between various Buhlmann GF settings and the DSAT algorithm?

Sorry - I've edited my post to add:

So, within normal no-deco recreational limits, how do bottom times for repetitive dives compare between DSAT computers like Oceanic and a Shearwater set to OC Rec Low (45/95)?

 

[scubadada]

My post, above, pertains to NDLs

 

[wedivebc]

Since the GF numbers describe a ratio between m-value at deepest stop (low number) and m-value surfacing (high number), only the high number would actually apply to the NDL since it applies to the surfacing gradient. You can change the number to anything you like between 1-100 and somewhere in there you'd have NDL run times that approximate recreational dive computers or possibly DSAT but since the algorithm used in most recreational is some variant of Buhlmann with some padding or tweak built in you would just have to do some side by side comparison to find the number you're looking for.