Perdix Ndls

[uncfnp]

I just got my old vyper out and confirmed you are wrong. I dont mean that in a rude way at all so please dont take offense but I did a dive plan on air on both the suunto vyper and my perdix. At 90 feet it says 22 while the perdix says 20min. The perdix is more conservative...yes only by a couple minutes...but none the less suunto is one of the most conservative computers and it surprised me the perdix even on low was still more conservative.

Actually I am not wrong and no offense intended. I have both computers in front of me. I did say it was a Cressi and not a Suunto and on nitrox.

So went back and ran air for comparison. Both on low, the Cressi takes over at roughly 60 feet. Cressi NDL on air at 58 feet is 50. On Petrel at 60 it is 49. (For comparison at 88 feet its 22 also for the Cressi so essentially the same as your Suunto).

But on nitrox, at 88 feet the Cressi NDL is 32 and at 90 its 31 on the Petrel. Interesting. Seems like something more then just EAD at play here.

 

[Bigeclipse]

and that is why i tell everyone that is interested in this sort of diving that you should get at least some sort of decompression training. a 5 minute back gas deco opens up so many more opportunities....

I'm going to for tec 40-50 next spring. This is just tempory...

 

[Bigeclipse]

Actual I am not wrong and no offense intended. I have both computers in front of me. I did say it was a Cressi and not a Suunto.

That is what I should have stated sorry. I meant to type you are wrong about the suunto. I also see you meant things change depending on depth and that is where I am concerned most. For example...we may have a deep 100ft dive and a few extra minutes can make all the world when you already have such a short time in recreational diving at those depths. I'm less concerned about having the perdix on medium for consecutive dives...but low in the first dive seems valid.

 

[Bigeclipse]

yes and no. If you are diving square profiles, then they should be within a minute or so of each other, but what doesn't change is the fact that the DSAT algorithm puts you at the surface with the same theoretical tissue loading as the computer, which may or may not be safe for repetitive diving, adverse conditions, etc etc.

Tbone...would it be a bad idea for my 2 dive scenerio to set the perdix on low conservatism for a deeper first dive to simulate other dive computer NDLs and then switch the conservatism to medium for the consecutive dives after?

 

[uncfnp]

..but none the less suunto is one of the most conservative computers and it surprised me the perdix even on low was still more conservative.

And that is a great example why one can not use conservative and liberal in any absolute way with algorithms. Even comparing two dive computers on one dive, it changes just with depth. Then add all the other variables. Conservative and liberal are only generalizations.

 

[uncfnp]

That is what I should have stated sorry. I meant to type you are wrong about the suunto. I also see you meant things change depending on depth and that is where I am concerned most. For example...we may have a deep 100ft dive and a few extra minutes can make all the world when you already have such a short time in recreational diving at those depths. I'm less concerned about having the perdix on medium for consecutive dives...but low in the first dive seems valid.

No problem. And remember, unless you all dive shoulder to shoulder there will be some variation between computers, even ones running the same algorithms.

 

[tbone1004]

Tbone...would it be a bad idea for my 2 dive scenerio to set the perdix on low conservatism for a deeper first dive to simulate other dive computer NDLs and then switch the conservatism to medium for the consecutive dives after?

I would commit to the profile that you believe will be the best for you under that specific dive scenario. That may be low/med/high depending on the day, too many variables. I personally would commit to the Perdix under whatever conservatism you believe will be best for you and say f-it to the other computers.

My personal opinion? I think the low conservatism is not safe for me based on the diving that I do and my medical history of bad joints unless I am diving in the caribbean or some equally irrelevant place for dive profiles *take no offense to that but reef diving is basically a glorified swimming pool, which is great for relaxation*. If I was diving in the mid-Atlantic, I wouldn't dive anything but the "high" conservatism, but I don't care about mandatory decompression, and that gradient factor coincides with my risk tolerance for DCS.

 

[Stoo]

and that is why i tell everyone that is interested in this sort of diving that you should get at least some sort of decompression training. a 5 minute back gas deco opens up so many more opportunities....

This tbone guy seems to be very sensible. The OP should follow this advice. Having a good idea of how this whole deco stuff works is really helpful in terms of determining the changes you might want to make in how your computer is behaving.

 

[Stoo]

All of which reminds me:

 

[uncfnp]

This tbone guy seems to be very sensible. The OP should follow this advice. Having a good idea of how this whole deco stuff works is really helpful in terms of determining the changes you might want to make in how your computer is behaving.

I agree, more knowledge and understanding of decompression theory is the ideal goal. But I believe the whole point of the recreational mode on the Shearwaters is for the average recreational diver to be able to use it with the average recreational divers level of theory. Adjusting the GF setting in recreational mode is no more risky then adjusting CF on the Geo. In fact, as the OP has pointed out, in some instances the most "liberal" setting in the Shearwater's rec mode is more conservative then some other DC's specifically marketed as recreational. Certainly more conservative then any computer running pure DSAT.