Computer or Not

[rjack321]

That's in my PADI EAN32 table so I'm sure it's tried and tested by plenty of divers, though that table requires a 3min safety stop at 15 ft for this dive.

The NOAA EAN32 table gives 100 min at 60'.

http://www.ndc.noaa.gov/dp_forms.html

I played around with decoplanner this AM. It gives 5 minutes total stop time for a 60 ft/90 min dive. As you back off the time to 70ish minutes the deco time goes down to a total of 3 mins.

I guess if I had a particular goal needing 90 mins to accomplish it might be worth it. I' cold at 60 mins anyway.

 

[WarmWaterDiver]

I also know empirically my NiTek3 and IQ-700 do not display identical NDL's on the same dive - as I've worn them together. The IQ-700 is slightly (VERY slightly) more conservative in my experience. The IQ-700 also displays slightly greater time to desaturate after a given dive than my NiTek3 does.

 

[rjack321]

I suspect some manufacturers are truncating the # of compartments because the really slow ones are irrelevant.

Buehlman's original paper had 16 compartments in both tables 16b and 16c.

 

[WarmWaterDiver]

I think you may be mistaken - the Dive Rite manuals & TUSA manuals list the same half-time for the slowest and fastest compartment used. I suspect the 'middle' compartments are more variable.

 

[rjack321]

I think you may be mistaken - the Dive Rite manuals & TUSA manuals list the same half-time for the slowest and fastest compartment used. I suspect the 'middle' compartments are more variable.

I meant that they use 8, 10, 12 etc. compartments. Some number smaller than what Buehlmann published in Decompression, Decompression Sickness, which was 16 compartments.

Changing the "middle" compartment half times would have the biggest influence over an actual dive and probably explains the differences you've noted.

 

[WarmWaterDiver]

If varying the 'middle' compartments would have the greatest effect, why have I observed such a small difference between 2 models using the same Buhlmann algorithm variant (according to the documentation) and 5 to 640 minute half-times at the extremes, but one has 25% fewer compartments than the other?

Which compartments would have the smallest effect when reduced in number by 25%?

I've never seen the NDL time remaining vary by more than 2 minutes between these models on my dives. On a vacation dive day where I've say made 2 or 3 day dives and a night dive, both models may well show around 24 hours time to desat (or greater) - but they may vary by about 15 minutes total in calculated time to desat - a quite small percentage of the 24 hour neighborhood.

 

[rjack321]

The fast half times rarely control the time of your no-deco dive. They get saturated within a few minutes of when you arrive on the bottom. Fortunately, they off-gas just about as fast (depending on who you ask)

The slow compartments, like hundreds of minutes never approach stauration on the longest of NDL dives. Unless your surface intervals are shorter than your dives, they don't play much of a role in multi-dive trips either.

The middle range of half times e.g. 15, 30, 45 minutes have the strongest influence over your NDL dive. Short enough to get (near) saturated, but not so fast so as to off-gas via a 30ft/min ascent and safety stops.

Having fewer compartments wouldn't necessarily mean big differences in times. Its the whole range that's controlling the dive just at different dive times

 

[WarmWaterDiver]

I can send you my electronic dive log if you would like, if you download the TUSA PC software and provide an e-mail address.

The slowest compartment typically controls time to desat - as this works as compartments in series as I understand it. This factors in to MY dive trips, for my estimation on time to fly - if time to desat shows > 24 hours, I personally take my time to fly is > 24 hours. Anything < 24 hours on time to desat I still treat as 24 hours minimum before time to fly.

maybe they don't factor into your dive trips?

If my fastest compartments get saturated within a few minutes of arriving at the bottom, why do I not have 0 NDL time when these become 'saturated'? What is your definition of 'saturated'?

 

[rjack321]

I can send you my electronic dive log if you would like, if you download the TUSA PC software and provide an e-mail address.

The slowest compartment typically controls time to desat - as this works as compartments in series as I understand it. This factors in to MY dive trips, for my estimation on time to fly - if time to desat shows > 24 hours, I personally take my time to fly is > 24 hours. Anything < 24 hours on time to desat I still treat as 24 hours minimum before time to fly.

Time to desat is not the same as controlling a dive. Of course the slowest compartment will be the last to clear. But you can easily make repetitive dives without a 500 minute half time compartment making a bit of a difference on your NDL.

maybe they don't factor into your dive trips?

24 hours works for me. Is your 'puter giving you "time to fly" longer than this?

If my fastest compartments get saturated within a few minutes of arriving at the bottom, why do I not have 0 NDL time when these become 'saturated'? What is your definition of 'saturated'?

Saturated = at equilibrium with ambient pressure.

Because they off-gas so fast, its not that big deal. You can ascend at a reasonable rate and not have excessive bubbling. These compartments, e.g 5 minute, illustrate that really - every dive is a deco dive at when you get right down to the nitty gritty.

 

[Jason Ooi]

I used dive computer monitoring my current dive profile and 2 backup plan on my slate