Deco on Dives in Coz? Educate Me

[Offroad]

On our last deep dive this year, we dove Punta Sur Cathedral. On the pre-dive briefing the divemaster told us that there was a number of swim through's and if we moved along well we could do them all on that dive. He also mentioned that if we went into deco, it would not be a problem.

My wife and I like the swim through's and normally follow the dive master on all of them when other divers sometimes hover overhead in shallower water. We dive with Oceanic and Aeris computers which have a liberal profile. When we were getting ready to head into the last swim through, mine was down to 2 minutes of bottom time and since we have never pushed them into deco, I took a path up and around the outside of the reef to move to shallower water. We were 3rd and 4th behind the DM and the rest of the group followed us instead of the DM and the first two divers. We just waited a few minutes on the top of the reef for the DM and other divers to pop out and we all started slowly up for our safety stop.

On the boat, one of the divers who followed the DM through the last swim through said her computer went into Deco but came out quickly. It sounded to me like the diver who went into deco just followed the DM and when she moved to shallower water her computer removed the deco obligation. I would have assumed from reading my computers manual that once it asked for a deco stop at a particular depth, if you didn't follow it the computer would be bent and locked out.

I know from our manuals and Oceanic/Aeris operational videos, what our computers will ask for if pushed into deco, but not having done one I have some questions:

Isn't it likely that once pushed into deco, different computers will be asking for different stops for different amounts of time? Shouldn't all deco stops be followed to completion as asked by that individual computer? It seems like this might make staying together as a group a bit more difficult. Maybe I'm a bit too conservative but I'm more comfortable moving to shallower water prior to a deco obligation. I don't mind diving a liberal computer to fairly low DTR but we also try to do longer than required safety stops whenever we are not holding the group up. Any advice for a complete deco newbie is appreciated.

Thanks

 

[cvchief]

I know my wife's mares puck slippped into deco on our last trip. She accended a bit and that apparently took care of the deco obligation. She did the same thing on a previous trip. As I strapped the thing on her and didnt really tell her anything about it, she never noticed. I saw it when I downloaded the dives off the puck. However the profile itself took care of it as we slowly came up. (Yes I know thats bad and we went over it before the last trip so she knows to accend a bit when its running out of time.)
Of course being an airhog, I have less chance of having to worry about it. She on the other hand could stay down and wait for us to come back on our second tank.....

 

[Offroad]

I know my wife's mares puck slippped into deco on our last trip. She accended a bit and that apparently took care of the deco obligation.

Maybe this is more common on the type of deep profiles used in Coz than I would have expected.

 

[Mr Carcharodon]

Isn't it likely that once pushed into deco, different computers will be asking for different stops for different amounts of time?
Thanks

To answer your question you are right that differnet computers will do ascents that have differences in how long you stop and at what depths. But if you skip a stop the computer will recalculate and add time to the shallower stops. You will not be locked out until you get to the surface. The intent of locking you out is to force an extended stop at the surface.

If you go just a few minutes into deco adding a minute at your safety stop for each minute you go into deco should clear your computer. It would be even better if you slow your ascent from half max depth up to the surface, with most of the time spent between 30 fsw and 10 fsw. Anyway different divers having computers that provide different plans is a problem. One way to resolve that is to have an plan of how to clear deco and get eveyone you dive with to follow that. If that cannot be done staying out of deco is safer.

 

[Offroad]

But if you skip a stop the computer will recalculate and add time to the shallower stops. You will not be locked out until you get to the surface.

If you go just a few minutes into deco adding a minute at your safety stop for each minute you go into deco should clear your computer. It would be even better if you slow your ascent from half max depth up to the surface, with most of the time spent between 30 fsw and 10 fsw.

Thanks for the explanation, sounds like we would have been fine following the DM on that dive, ascending slowly to our safety stop and adding some time to our normal 5 minutes or so. I guess the point is, we should see the computers clear the deco obligation and then add the safety stop.

 

[deborahdelamar]

The DM will plan the trip as a non-decompression day. All is considered: Experience of the divers, choices of sites, multilevel plans & max depths, length of SI are all part of the equation and the briefings are clear. I've never been on a dive where everyone in the group ended together. The DM shoots a buoy and divers ascend close to it as appropriate for them. Long safety stops are OK and advised -- many ops use 5 minutes as a minimum and none will be angry if you want longer than 3 unless they have other problems at hand...

SOP in Coz is 700psi to begin your ascent to the safety stop -- gradual, of course -- no dash for the surface so you can continue to enjoy yourself. If you see that you're nearing the NDL, simply dive a bit shallower to gain time. With most computers, there is a safety factor when you hit the NDL and a deco stop is not automatic. You may go into deco at one depth and come out of it as you ascend. However, if you're skirting the NDL prematurely in the dive, you need to make an adjustment ASAP. And you should honestly monitor your air -- Do you have a few hundred PSI extra for say, a 20-minute stop and slow ascent after?

What happens sometimes is that a distraction at the end of the dive (a lionfish, a shark, an incident of some kind) may lead you to a mandatory stop.

In summary, remain aware of what your instruments are telling you.

 

[georoc01]

Yes, as you go shallower your computer will gradually remove your deco obligation. You can clear it before you reach the mandatory stops. If you skip a stop the computer will go into violation, but if you clear it before you hit that depth, you are fine.

I was doing deco dives as part of at tech class with two computers. I notified one computer that I had switched to 100% o2 but not the other so the 2nd computer never cleared. But most of the time, my computers would clear before we hit the final stop.

 

[Offroad]

Yes, as you go shallower your computer will gradually remove your deco obligation. You can clear it before you reach the mandatory stops. If you skip a stop the computer will go into violation, but if you clear it before you hit that depth, you are fine.

Ok, now I'm confused again.
The post below indicates I can skip a stop and not be locked out, but the computer will add time to shallower stops.

But if you skip a stop the computer will recalculate and add time to the shallower stops. You will not be locked out until you get to the surface.

If you go just a few minutes into deco adding a minute at your safety stop for each minute you go into deco should clear your computer. It would be even better if you slow your ascent from half max depth up to the surface, with most of the time spent between 30 fsw and 10 fsw.

 

[scubawife]

Theoretically, every dive is a deco dive because don't we all make a 3-5 minute "safety stop" at the end of any dive? What's the purpose? To nitrogen off-gass before ascending to the surface. When your computer actually hits "deco" on a dive, if it's a properly planned multi-level dive as most Cozumel dives are, as long as you're aware of your air, you should be fine.

I dive with the same brand computers and have dived Punta Sur, Maracaibo and a couple other deep sites in Cozumel where we did the dive expecting some deco. If you are aware of your air consumption rate, allow enough time and air, having your computer go into the warning zone or even go into deco is not a big deal. We know going into the dive that we could end up with an additional deco obligation and it's never been an issue. As you multi-level up from depth, your computer should indicate a ceiling that you can't go above until a certain deco obligation has been met. If you blow a stop, the computer will usually add time to on to a shallower depth. At least with the Oceanic and Aeris computers I've had, if you ignore your computer and do surface w/o meeting your obligation, the computer locks out for 24hrs... but with proper multi-level dive planning and awareness, that should never be an issue. When I dive with my Aeris or Oceanic, I'm usually the last diver in the group to hit the warning or deco zone, and the first out of it. They are VERY liberal computers and I know that. I tend to dive more conservatively then my computer allows, but on the few occasions when I plan to push the limits, I still prefer the liberal computer over my other computer, a Mares, that at times verges on ridiculous even under the most conservative diving plans.

 

[georoc01]

Ok, now I'm confused again.
The post below indicates I can skip a stop and not be locked out, but the computer will add time to shallower stops.

Yes, if you skip a stop at 50 feet, it will add time to future stops.

Generally it starts first adding a mandatory stop at 10 feet. Then as you extend your deco, it will add stops incrementally deeper. It will recalculate deeper stops if you go shallower, or flash for you to go back to the stop you skipped. That may depend on your computer.

But if you surface w/o doing your deco obligation, your computer will lock out for at least 24 hours. After locking my atom 2.0 out pretty good, it took 48 hours to completely clear.