Suunto Vyper and EAN non deco limits

[DickBurton]

Hi

I've been diving for a couple of years now and finally got round to getting my Nitrox certification. In the PADI book that accompanied the course it states that the non deco time at 18 metres with 32% EAN is 95 minutes. My Suunto Vyper tells me I can only stay at 18 metres for 74 minutes (I've not dived for a few days so it's nothing to do with repetetive dives), my partners Suunto D4 tells her she can stay at the same depth for 81 minutes!

I'm assuming that there is nothing wrong with either computer and I'm happy to stick with conservative limits, but the differences to seem quite significant - especially noticable at 30 metres. Can anyone tell me - is this just the Suunto algorithm being ulta conservative?

Thanks

 

[HungoverDiver]

Suunto computers use the Reduced gradient bubble model (RGBM). This is the most conservative model of decompression stop/nitrogen loading. Although it's a bit odd that the two Suunto's have different NDL for EAN32.

Reduced gradient bubble model - Wikipedia, the free encyclopedia

 

[RonR]

There is actually nothing inherently more or less conservative about RGBM as an algorithm- it's entirely dependent on the settings selected by the individual computer manufacturer. Suunto's implementation of RGBM has a reputation of being very conservative. Others, like Atomic's, are less so.


Are there differences in the settings for the two computers? Most allow you to adjust personal settings or conservatism in some way. It's also the case that any differences between computers will seem exaggerated if you look at NDLs on shallow dives, because we treat decompression as a binary on-off setting, which it isn't. A 10% variation in NDL's at 18 m may not represent much of a difference at all. I can make mine give either 76 or 80 minutes at 19 m with 32% EAN by changing conservatism settings. Significant differences at 30 m however might be due to settings or actual changes in the algorithm implementation.

 

[HungoverDiver]

it's entirely dependent on the settings selected by the individual computer manufacturer.

Ah, good to know. I always assumed Suunto = conservative = RGBM. Fun times

Suunto is annoyingly conservative though.

 

[Hatul]

Some of the Suuntos allow you to set 50% RGBM, which is a more liberal version. Perhaps her D4 is set to this?

My experience with the Vyper compared to my Galileo is the Suunto is much more conservative on repetitive dives, especially if the surface interval is short.

 

[DickBurton]

Thanks for the replies. The only way I can see to change the calculation is to change the altitude or select an even more conservative program. I have used the default settings, which I believe are least conservative. I didn't know about the RGBM setting on the D4 - I'll check later.

 

[miketsp]

..snip..
Suunto is annoyingly conservative though.

I've been diving my VYPER for many years now and I've always found it very predictable with just the amount of conservatism that I like to have.
But I wasn't prepared for what happened on one particular dive. My wife and I got on the boat with the tanks filled to EAN36 and EAN40, the plan being to do a first dive to 26m. But there was a forced change of plan and we shifted to a wreck at 32 - 33m.
So as usual I planned on tables and saw the NOAA exposure limits of 150mins at 1.4, 120mins at 1.5 and 45mins at 1.6. Knowing that this was going to be a very effortless dive and our good SACs we planned our bottom time to be 30mins based on our rock-bottom and I accepted the 1.6 limit.
So we started the dive and although I had expected the constant PO2 alarm at around 1.5 I was surprised by the rapid climb of the OLF bar graph.
Both Vypers toxed us out at a 100% OLF after only 22mins. No deco time was still 13 mins and we still had a lot of gas in the tanks.
So without quite understanding we aborted the dive and got back on the boat.
Accessing SB later I found this thread
http://www.scubaboard.com/forums/computers-gauges-watches-analyzers/31655-suunto-vyper-%2A%2Aserious-bug%2A%2A-cns-o2-computation.html

with the explanation about the VYPER's accelerated O2 loading beyond 1.4. Something I wasn't previously aware of.
If I'd known we'd have finished our planned dive normally.

 

[Hatul]

I also felt the wrath of my Vyper when I did a second dive after a short 47 min surface interval. Even though the second dive was well within non deco limits by my Galileo (even with MB level set to 1) the Vyper went into significant deco.