Dive computer basics

[Diver Dennis]

It will give you a read out.."Kiss your *** goodbye". (assuming you are on an 80 filled with air...)


Seriously though, I think you might have meant just going into deco at a reasonable depth, in which case it should give you instruction on the stop. If you go into deco for just a couple of minutes on a multi-level dive chances are you will be clear before you reach a mandated stop.

 

[ianr33]

. The Aeris computers, just like other computers made by Pelagic and sold under Oceanic and Sherwood brands, use one decompression algorithm for NDL calculations and a different model for calculating mandatory decompression stops.

Hi Charlie. Could you expand on that a bit? I often take my Aeris computer along for the ride on deco dives and have seen it do some very strange things. In particular if a second dive is deeper and involves deco the computer comes back with a huge amount of deco time (maybe 60 minutes compared to 10 from V planner)

 

[Charlie99]

Hi Charlie. Could you expand on that a bit? I often take my Aeris computer along for the ride on deco dives and have seen it do some very strange things. In particular if a second dive is deeper and involves deco the computer comes back with a huge amount of deco time (maybe 60 minutes compared to 10 from V planner)

The PelagicOceanic computers that I am familiar with, and I'm reasonably certain also the Aeris/Pelagic computer you have, base the NDL calculations on the DSAT/PADI decompression model.

The DSAT model is unique in that it is an NDL model only. More specifically, it has only the M0 or surfacing compartment limits, and does not have any delta-m info -- the slope information that says how M values change with depth. The M values + delta-M values are used together to figure out the compartment limits at a stop depth such as 10'. To get decompression stop times, Pelagic borrowed a bit from the Workmann/USN model, but since it has higher M0 values, they had to do a bit of kludging to get the computer to behave rationally at the transition between NDL and mandatory deco. Or maybe they just picked very conservative delta M values.

I don't know the specifics of what causes the behavior that you have noted, but many divers in the UK, where a large percentage of divers routinely have signficant decompression obligations, have also noted that sort of ultra-conservative behavior when used on a dive with significant deco.

I'm a single tank diver that rarely gets more than a few minutes into deco, so it hasn't been an issue for me.

 

[ianr33]

Thanks Charlie.

If I am being lazy I will follow my computer up to around 10 minutes of deco indicated.Anything more than that is a tables dive,most likely with deco tanks(s)

It is interesting though that the Pelagic computers are really quite aggressive on NDL dives but then become hyper conservative once into significant deco. My take on that is that they were never intended to be used as deco computers,dont really know how to handle it and so play it safe.

 

[diver 85]

The way I read it the OP was asking a question---not saying he/she was going there or even planning on going there for that long, basically looking for info......

 

[LavaSurfer]

When Diving a Aeris XR2 computer, If I go past the deco limits, say 200 feet for 30 min, will it let me know what to do at that point, (assuming I was not planning on doing this).

To answer your question:
DiveAeris.com - Scuba Diving Computers - XR-2
toll-free: (800) 647-0605


I can only assume why you would ask a question so bazaar as certainly you would not really do this dive by accident or even on purpose without proper planning and training. In case you were serious, Here is a deco schedule that you might be faced with on air alone. It is not trivial and your Aeris computer is not designed for this type of diving.


Dec to 200ft (4) on Air, 50ft/min descent.
Level 200ft 16:00 (20) on Air, 1.48 ppO2, 200ft ead
Asc to 110ft (23) on Air, -30ft/min ascent.
Stop at 110ft 1:00 (24) on Air, 0.91 ppO2, 110ft ead
Stop at 100ft 1:00 (25) on Air, 0.85 ppO2, 100ft ead
Stop at 90ft 2:00 (27) on Air, 0.78 ppO2, 90ft ead
Stop at 80ft 2:00 (29) on Air, 0.72 ppO2, 80ft ead
Stop at 70ft 3:00 (32) on Air, 0.65 ppO2, 70ft ead
Stop at 60ft 3:00 (35) on Air, 0.59 ppO2, 60ft ead
Stop at 50ft 6:00 (41) on Air, 0.53 ppO2, 50ft ead
Stop at 40ft 6:00 (47) on Air, 0.46 ppO2, 40ft ead
Stop at 30ft 10:00 (57) on Air, 0.40 ppO2, 30ft ead
Stop at 20ft 15:00 (72) on Air, 0.34 ppO2, 20ft ead
Stop at 10ft 26:00 (98) on Air, 0.27 ppO2, 10ft ead
Asc to sfc. (98) on Air, -30ft/min ascent.

Off gassing starts at 137.9ft

OTU's this dive: 42
CNS Total: 18.4%

190.6 cu ft Air
190.6 cu ft TOTAL
DIVE PLAN COMPLETE

 

[mello-yellow]

It will give you a read out.."Kiss your *** goodbye". (assuming you are on an 80 filled with air...)

My computer actually has this message! Well, almost

It has a special display which the manual says "is inconceivable will ever come up". It occures if one of the following conditions is met:

1. Total continuous bottom time 10 hours or more
2. Depth 500 feet or more
3. First obligatory deco stop deeper than 40 feet*

Once that display occures it will not change until the computer is taken out of the water -- most likely by rescue personnel.

* I know, that one is not COMPLETELY inconceivable

 

[SailNaked]

Ok just to be clear I have no intention of staying at 200 feet for 30 minute, And I do not want to know anything about that dive. I could not remeber the max No Decomp for something reasonable so posted that example. what I am interested in is if a dive computer can give you useful information after it goes past its limits, my manual says it will warn me for 10 sec then go to guage mode, and after 5 minutes on the surface will effectively lock up if I go above the deco schedule. So I was curious if I am not paying attention (miss the 10 sec beeping) at say 140 feet and I go over whatever it is that im supposed to be at by a minute and then go above the stop for a few seconds will the computer ever give up on my stupidity and just flash "shouldnt have done that" at me? or will it allow me to get back under the deco stop and calculate how long I should stay there for my own good and happiness.

 

[ianr33]

The above schedule is for only 20 minutes bottom time. Original question was for 30.

 

[ianr33]

Ok just to be clear I have no intention of staying at 200 feet for 30 minute, And I do not want to know anything about that dive. I could not remeber the max No Decomp for something reasonable so posted that example. what I am interested in is if a dive computer can give you useful information after it goes past its limits, my manual says it will warn me for 10 sec then go to guage mode, and after 5 minutes on the surface will effectively lock up if I go above the deco schedule. So I was curious if I am not paying attention (miss the 10 sec beeping) at say 140 feet and I go over whatever it is that im supposed to be at by a minute and then go above the stop for a few seconds will the computer ever give up on my stupidity and just flash "shouldnt have done that" at me? or will it allow me to get back under the deco stop and calculate how long I should stay there for my own good and happiness.

If you go into deco at 140 feet the computer will give you a stop at 10 feet. Initially that will be 1 minute at 10 feet. This time will gradually increase.Eventually it will give you one minute at 20 feet. (And maybe 20 minutes at 10 feet as well,depends on algorithm and profile etc.etc)

If you then ascend shallower than that deco "ceiling" it will start complaining.Stay above it longer than 30 seconds or whatever it allows it will give up on you completly and go into gauge mode once you have surfaced.

If I was at 140 feet and my computer was telling me to do a 5 minute stop at 10 feet this is what I would do:

Ascend to 70 feet (at 30 feet/min) Pause there.Slowly ascend to 20 feet (At about 10 feet/min)
Stop at 20 feet until the deco obligation has cleared. (If the computer is asking for 5 minutes at 10 feet it will need about 8 minutes to clear at 20 feet)

Ascend to 10 feet and wait for the computer to go green.

The above works great IF you have enough gas to do it. If you dont then ascend directly to 10 feet and wait as long as you have something to breathe. If you survive be thankful that somebody was looking over you and sign up for a deco course !!