Deco Diving - Computer Help Needed (Cobra 3, or others!)

[dmoore19]

If you are interested, you might try reading this book. http://www.amazon.com/gp/offer-listing/1905492073/ref=dp_olp_new?ie=UTF8&condition=new It explains a lot and might give you some insight as to what the computer is telling you.

 

[bbarnett51]

Yes, the Cobra will start to count down when you reach the appropriate depth. If you go into deco on a recreational dive your cobra will give you a cieling of 10'. It usually adds a few minutes to your safety stop but your safety stop is no longer voluntary its mandatory.

The cobra safety stop starts at 15' and starts over if you go below 20'.

 

[Slmason.72]

So, based on the screen of the Cobra 3, if I accidentally enter deco mode and I am at 75 feet, and the computer displays a ceiling of 30 feet, and an ascent time of 10 minutes, and if it takes me two minutes to reach the ceiling of 30 feet, and my ascent time now says 8 minutes (because I just traveled up for two minutes), does that now mean that I have to stay at this ceiling of 30 feet for the 8 minutes (meaning that my ascent time becomes, or equals, my deco countdown time to stay at the ceiling for decompresion)?

No, the 10 minutes ascent time you see at 75 feet is the total ascent time including the time it takes to rise through the water column and the time(s) you must spend at each deco stop. I don't have a cobra, but do dive a D6 (also a Suunto product) and assume the display logic to be very similar based on your comments. I have encountered a few mandatory 15 foot stops due to ascent rate violations and also use the 'deep stop' option which displays like the 15 foot stop. I ran a deco scenario on the "i dive comp' computer simulator and it showed the compute reacting differently than the suggested safety stops... The simulator showed that As you ascend past the first 'floor', as long as you remain between the ceiling and floor (say 20 feet and 33 feet) you will see the two arrows indicating you are between these depths. The total ascent time will begin to decrease. Once you have completed your stop at that depth, the 'ceiling' number will change and the ascent time will not decrease further until you reach the new floor. Once the ascent time clears, you have completed your deco obligation.

Based on what I have seen for deep stops and what the simulation showed, I would expect to see one or the other behavior in real life. I know this gives two answers to your question, but at least you might know what to expect. Personally, I believe it will display the deco stops similar to the suggested deep and safety stops, and I'm glad you asked the question because should I ever find myself in that situation, I will now be looking for either behavior from my computer.

 

[DitrasetMan]

So, based on DivePal (which I have been using) and Alberto: when you enter deco mode, the remaining air time which is displayed on the left is replaced with the ceiling, which I need to go up to. And, the no deco time on the right is replaced with total ascent time. There is no specific deco countdown when you arrive at each deco stop.

Another question, assuming I have only one deco stop: does the Cobra 3 display the total ascent time from where you are until you reach the surface, or where you are until you have traveled up to the ceiling and completed your deco time? (you all are conflicting on this point). Does it incorporate the amount of time that will be necessary to stay at the mandatory safety stop? I understand what the arrows are telling you (up means go up to the ceiling, up and down mean stay where you are, and down arrow with "Er" means that you went above your ceiling and need to go beneath it immediately). I have noticed that when using the computer in the simulator, as I am traveling up to the ceiling, the ASC time decreases (probably because I am decompressing on the way to the ceiling), but then I wait at the ceiling for the ascent time to become zero, indicating that I am supposed to wait for ASC time to become zero at the ceiling (therefore it does not take into consideration the time to get to and wait at the mandatory safety stop, or the time to get to the surface). What if there are multiple deco stops, how long will I know to wait - simply rely on the arrows?
.

So....

 

[DuboisP]

Deco = Technical. Don't you french people know that!

oh !

for french divers, deco is not technical, it's normal. :blinking:
technical begins at 40m and nitrox/O² pony for decompression.

 

[DiveNav]

.....Does it incorporate the amount of time that will be necessary to stay at the mandatory safety stop? .....

A mandatory safety stop is usually called a "deco stop" ....

.....assuming I have only one deco stop: does the Cobra 3 display the total ascent time from where you are until you reach the surface, or where you are until you have traveled up to the ceiling and completed your deco time? (you all are conflicting on this point). Does it incorporate the amount of time that will be necessary to stay at the mandatory safety stop? ......

The definition of TAT (Total Ascent Time) is the time it takes to reach the surface from "where you are at any given point" and includes vertical travel time and deco stop time(s).

Where it gets "confusing" is at the last deco stop. Let me explain.
Let's assume that the computer is telling you: "10ft and 2 minutes", and you are at 15ft (perfectly OK as it is a depth between the floor and the ceiling) .... after a bit the computer shows "10ft and 1 minute". This 1 minute in theory includes the 30 seconds of vertical time (from 15ft to the surface) and a remaining 30 seconds of deco stop at 10ft.
After another bit the deco situation clears and the computer reverts to normal dive mode showing the no deco time.
In theory now you could ascend as you are not in deco anymore .... but do you really want to cut it so close? Most likely one of your tissue compartments is ~99% ....

Me? If I have enough gas I would stay few minutes more at 15ft

Alberto (aka eDiver)

 

[DevonDiver]

for french divers, deco is not technical, it's normal. :blinking:
technical begins at 40m and nitrox/O² pony for decompression.

..for CMAS divers. I'm sure a French diver, trained with PADI, SSI et al, wouldn't share that view.

Then again, CMAS (and BSAC) diving training is substantially different to the other 'mainstream' agencies...

The point being... dive only within the limits of your training and experience. A golden-recommendation that spans all agencies, approaches and perspectives..

A mandatory safety stop is usually called a "deco stop" ....

A mandatory safety stop is a mandatory safety stop. A deco stop is a deco stop.

If an agency (let's say 'PADI') include a mandatory safety stop in their tables procedures, then the nature of that stop shouldn't be re-defined to meet alternative definitions.

A mandatory safety stop is not a 'ceiling'.

PADI recreational RDP divers, inside NDL limits, always have immediate access to the surface, via direct ascent, in the event of an emergency. They should, however, plan to complete a safety stop as a matter of course, given the pre-requisite dive profile factors (i.e. deeper than 30m/within 3 PGs of an NDL etc).

The word 'mandatory' exists only in respect to dive planning, not emergency protocol or procedure. It is, and will remain, only a safety stop - a pause in ascent to increase conservatism in relation to DCS risk.

A deco stop is a 'ceiling'.

Whist not a physical barrier, such as being in a cave or wreck, it is a virtual barrier against ascent. The 'virtual' concept issues from the unreasonable probability of DCS, if that barrier is exceeded. A diver with deco obligation does not have immediate access to the surface, even if a conflicting emergency/contingency demands it.

To resort to that 'immediate access', at the expense of deco obligation, may be the 'lesser of two evils'... but is still likely to prove 'quite evil'.

 

[ajduplessis]

This tread reminds me of an incident last year when a recreational diver asked me the same question to "extend" his knowledge. His words "I want to get a better understanding of deco and how my computer work. I have no intention of going into deco....." Only to find out the next week that he got bent on deco dive.

 

[eelnoraa]

I have the same concern as AJ.

So to OP, even if you know exactly how your Cobra function in deco mode, please make an efford so that you will never see it.

 

[dumpsterDiver]

This tread reminds me of an incident last year when a recreational diver asked me the same question to "extend" his knowledge. His words "I want to get a better understanding of deco and how my computer work. I have no intention of going into deco....." Only to find out the next week that he got bent on deco dive.

Well I guess you did not do a very good job DID YOU!