Beyond 130 feet: always a deco dive?

[Dive Bug Bit Me]

4 inches definitely doesn't give you a lot of room for error, I agree for sure.

I cut tables for technical dives in GAP so my computer is considered backup to them. I plan to never end a dive until I have completed the run schedule according to those tables and cleared my computer just to add a little more conservatism to the dive plan. My computer has never had remaining deco after the table schedule has completed, which is due to how I cut the plan in GAP (more conservative). Computer is a Uwatec Galileo Luna w/multi-gas capability.

I like the idea of using a tech computer as a back up to my tables. Thing is my computer will give different stops to my plan that was cut on software (iDeco or V-planner). Therefore when I ascend, I need to dive either the cut plan or the computer. If I do both, I end up with too many deep stops, invalidating my cut plan. If I skip some of the computer deep stops, the computer locks me into use tables mode. Curious to what your view is.

 

[James R]

I dive the table run schedule until the last stop is complete, then make sure my computer's also clear. My computer doesn't have deep stops so there's no issue between them there. Like I said before, the plans I cut have always been more conservative than my computer so I've yet to have to worry with it at all.

Eventually I will replace this computer with something more appropriate (and with OLED screen!) for technical diving and mixed gasses, which will allow me to run my table schedule exactly and adjust should I mess up and miss a stop etc.

 

[cbrich]

To be honest, it's not a PADI 'initiative'... the concept of padding your deco is hardly exclusive.. or new...

I think you missed the point. Look at the link and you see what chrpai was talking about.

http://www.scubadiverinfo.com/images/dive_tables_PADI_front.jpg

Look at the back side and you see what is being discussed. I am saying PADI put that statement on the RDP for legal reasons.

 

[chrpai]

I mentioned that just to illustrate another intepretation of what a safety stop is.

Personally, I like to think of it as all dives involve decompression, it's just the ceiling and duration might be as little as 0 and 0 depending on the scenario. What we call it is just words.

(As an aside, I'm not a technical diver so it's frequently 15'-20' for 3-5 minutes and a nice slow dive ascent over several minutes or more as I follow the bottom of Lake Travis back to my exit point. )

 

[DevonDiver]

Considering I've spent the last 10 years with a PADI RDP in my bag, I do understand the point. What I fail to understand is how that applied to decompression diving, as taught by TecRec (the name given to PADI's technical diving program).

The 'mandatory' safety stop is mandatory only in the sense of diving planning. For recreational dives. It is not a 'ceiling'... and it can be broken if other factors present a safety requirement to do so. In contrast, a decompression stop cannot be broken - it is a 'ceiling'.. an 'overhead'.

The difference, in a nutshell between stop classifications:

1) Recommended Safety Stop - "you'd be wise to do one"

2) Mandatory Safety Stop - "you'd be stupid not to do one"

3) Decompression Stop - "prepare to call an ambulance..."

 

[boulderjohn]

Out of curiosity, do most computers handle going beyond the NDL and dealing with deco, or are those a sort of emergency mode that the computer really shouldn't be in? Are there specific tech computers that are designed for deco?

All computers will do this, but if you read their manuals, they will tell you that it is to be used in case of emergency only and is not designed for planned decompression.

I like the idea of using a tech computer as a back up to my tables. Thing is my computer will give different stops to my plan that was cut on software (iDeco or V-planner). Therefore when I ascend, I need to dive either the cut plan or the computer. If I do both, I end up with too many deep stops, invalidating my cut plan. If I skip some of the computer deep stops, the computer locks me into use tables mode. Curious to what your view is.

Different tech oriented computers handle this differently. Just after the Suunto HelO2 came out, I did a pretty deep (261 feet) dive. My buddy and I planned it using V-Planner, and we followed it perfectly. He had just gotten a new HelO2, though, and he wanted to see what it could do. He tried his best to set the preferences as close as he could to the V-Planner schedule, but as we ascended, it got angrier and angrier at us as we ignored its commands. Finally, during either our 40 foot or 30 foot stop (I can't remember), it gave up on us and went into gauge mode, becoming perfectly worthless for us.

In contrast, other models of computer (like the Shearwater Predator) will keep adjusting every time you ignore it (as the HelO2 did), but will never quit on you, even if you leave the water with time remaining on it. This is an important issue for using computers for decompression diving, either when using computers to back up tables or using computers as your primary ascent device. If you are using them as your primary ascent device, you have to deal with the reality that not every computer on your dive team will agree, even if everyone has the same model. You have to determine before the dive which one you will follow in case of disagreement, and you can't do that with the fear that you are going to lose functionality of a computer for 48 hours because you chose to follow a different computer on that dive.

 

[Dive Bug Bit Me]

Agreed. My VR will beep, flash red and scream, but it will not abandon me.

Then again, by the time it is having an emotional melt down, I am not convinced how reliable its remaining deco plan really is. Hence I tend to choose an exit plan as I leave the bottom (so far always the cut plan) and use it. Clearing the computer, that admittedly is in meltdown mode, after my pre cut plan is done seems like one of those things that sounds cool in theory. . . .

Hence my question for those who insist on this as a procedure.

 

[ianr33]

Except, assuming you are following PADI/DSAT procedures, that within 3 pressure groups of an NDL the safety stops become `mandatory`. (Throwing gas on the fire just to make it more hazy!)

So then it becomes a mandatory optional stop? Or is it an optional mandatory stop??

I guess the ceiling too may be an arbitrary depth, but I'm pretty certain they are completely independent of one another.

Wrong tool for the job.

Agreed.

 

[boulderjohn]

I think you missed the point. Look at the link and you see what chrpai was talking about.

http://www.scubadiverinfo.com/images/dive_tables_PADI_front.jpg

Look at the back side and you see what is being discussed. I am saying PADI put that statement on the RDP for legal reasons.

The reasons don't have to be guessed at. The research was published in peer reviewed journals. PADI conducted extensive tests on divers and used Doppler bubble imaging to check their blood after dives. Their numbers were based on the results. The mandatory safety stop rule was established because their research indicated a gray area (literally on the tables) between dives that did not require a stop and dives that did.

You have to remember that in all cases we are dealing in probabilities and not absolutes. In the NDL dives, you are extremely unlikely to get DCS if you follow those numbers. If you go off the table, the likelihood increases to the extent that it was considered unacceptable to go without a decompression stop. The mandatory safety stop region is the transition between the acceptable risk and the unacceptable risk.

 

[mstachowsky]

So...would it be correct to say that a tec diver plans a deeper dive much more carefully, prints tables specific to the dive/gas profile, and uses the computer only as backup?