Deco on Dives in Coz? Educate Me

[BabyDuck]

the take-home is 'know thy computer'. they all do things differently. my rec computer will clear stops while i go up slowly, but some won't. see if you can find your manual & what it says it will do if you stay past ndl time.

 

[Mr Carcharodon]

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.

I think the point of confusion is about the terms “locked out” and “violation” not being the same. Computers will not lock you out while you are still in the water because the intention is give you the information to finish the dive safely. But once you get to the surface they may lock you out for a period of time which is intended to keep you from getting back in the water when you may be at risk for DCS. In this case “violation” means you went to a shallower depth than your computer wanted before it wanted you to. The shallowest allowable depth is the “ceiling”. For a NDL dive the ceiling is at the surface, and for a deco dive it is someplace below the surface. But if you are just a few minutes into deco the ceiling will likely be somewhere between 20 fsw and the surface so in that case a longer safety stop at 15 fsw is not going to be a lot different. But if you run over your NDL by more than say 5 minutes the first stop could be deeper than 20 fsw. At that point you really need a plan on what depths to stop at and for how long.

That dive in Coz was a deco dive even if it was pretty minor deco. The other thing to remember is that you need the gas to complete the stops because that slow ascent was not entirely optional.

I do think many of the operators in Coz are more casual about deco and gas planning than I would choose to be. Addmittaly the risks are still low. But they are higher than what would be sanctioned by any training agency I can think of. Part of this is about informed consent. The dive operators are taking you on dives with added risk but a lot of the divers are not aware of the risks they are taking.

 

[Offroad]

I think the point of confusion is about the terms “locked out” and “violation” not being the same. Computers will not lock you out while you are still in the water because the intention is give you the information to finish the dive safely. But once you get to the surface they may lock you out for a period of time which is intended to keep you from getting back in the water when you may be at risk for DCS. In this case “violation” means you went to a shallower depth than your computer wanted before it wanted you to. The shallowest allowable depth is the “ceiling”. For a NDL dive the ceiling is at the surface, and for a deco dive it is someplace below the surface. But if you are just a few minutes into deco the ceiling will likely be somewhere between 20 fsw and the surface so in that case a longer safety stop at 15 fsw is not going to be a lot different. But if you run over your NDL by more than say 5 minutes the first stop could be deeper than 20 fsw. At that point you really need a plan on what depths to stop at and for how long.

That dive in Coz was a deco dive even if it was pretty minor deco. The other thing to remember is that you need the gas to complete the stops because that slow ascent was not entirely optional.

Great explanation, thanks again.

I decided to finish the dive without any deco obligation because that's what I was comfortable with at the time. With the information I have learned (and will seek to learn), I may feel comfortable with going a few minutes into deco at some point in the future.

 

[MMM]

Based on my experience, DMs won't take divers onto dives where there is a potential deco situation before they have confidence in diver's air usage, buoyancy control and general comfort level. If I've demonstrated on many dives that my air consumption is such that I can safely manage any deco obligations, then what's the big whoop.

 

[Prop Joe]

I'm a Suunto user (very conservative) and have some obligations in my past. I'm getting older and I'm thinking the Suunto might not be all bad. My buddy does the same profile and never has obligation "issues" with his (liberal)Computer. We just do a nice muti-level acsent or hang a little longer at the "safety" till the Suunto clears. If you need to do a stop... Chasin' a fish for that perfect pic... You can never have enough gas. Plan accordingly. Always be prepared to pay the "Nitrogen Police".

I like steel 120's for instance. Some like 80's to save a few bucks. What do you save when you blow a stop for... What $10-15 bucks??? Give me the big tank please. I'd rather come up with extra gas than blow an obligation. Everyone will have an opinion on this...
Flame suit on.

 

[DandyDon]

I was just discussing knowing one's computer well, watching it and understanding it thru the dives in a private discussion. Good thread, altho it sounds like you didn't know what to expect. Does your model have a Simulated Dive feature? Great tool! I tried to take my home buddy on a one-minute deco practice dive at Santa Rosa NM once, but we're both such air hogs we had to do fast tank changes, get back down, and sit on the bottom grate to hit Red. We dive Oceanic computers which are no more liberal than Padi charts but can be difficult to Deco - except he wussed out, hovered 5 feet higher and watched me do it so didn't really get the experience.

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.)

That's about how we do it. He wears a computer so I can read it. :silly: We have the same brand and we have at least been thru Simulated deco dives but it's been so long he'd forgotten everything. All he has done for years are annual Cozumel trips and he forgot how to use his compass too.

We had 100 cf tanks for Cathedral last time tho and as the DM briefed, we went a couple of minutes into Deco - which cleared before we even got to the Safety Stop. There was some other confusion. I asked on the boat if he'd noticed he went Deco? Nope. I showed him on his. Asked if he noticed the beeping sound? What was that about anyway? :shocked2:

I often remind him that it's fine to dive an Oceanic into the Yellow as long as we work it back into the Green before or on the SS, but once you hit Red, I don't think you can. Low Yellow is the best you can hope for. We also noticed on downloads that we've both been casual about some other things to work on.

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.

Yeah, and know your machine well before you dive it. Manual study, download from OceanicWorldwide.com and read in large font if needed, Sim Dives if you can.

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.

Many models don't have Deep Safety Stops built into them if that's what you mean? Ours don't. We just had the required Deco stop for 10 ft I think it was, but cleared it ascending before we got to 20.

I've taken my Oceanic on a variety of Sim Dives, thinking about what I'd do in the water if it happened then while I was kinda narced (you will be even if you don't notice it; I don't) and it gets a little exciting watching, then relieving watching the Deco Obligation do down on ascent even before stops.

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.

Yeah, and you can lock up an Oceanic by screwing up Nitrox settings too; always turn Default off.

the take-home is 'know thy computer'. they all do things differently. my rec computer will clear stops while i go up slowly, but some won't. see if you can find your manual & what it says it will do if you stay past ndl time.

I bet you know yours well, but so many recreational divers buy em, wear em, not really knowing. Always good to download computer manuals to your PC; I do the same with cameras.

 

[Offroad]

I have been through the manual for my computer many times including the section on Deco, and I did know the icons it would use to direct you through an obligation. That said, I did not read that section before this trip and probably should have. I will do some simulation deco dives to get more familiar with handling that on this computer.

In reading my manual last night, I'm not sure this computer will recalculate if you miss a stop as some have mentioned, and add time to remaining stops to compensate. It calls ascending above a required stop for less than 5 minutes a "Conditional Violation". If you remain above a required stop for more than 5 minutes, its a "Delayed Violation". When you surface after a "Delayed Violation" 5 minutes later, you are in "Permanent Violation" (Locked Out). Nothing is mentioned about any recalculations for missed stops, but perhaps simulation mode would give more information. It would seem that only the "Conditional Violation" can be fixed by moving to the required stop within 5 minutes, after that I believe you are going to be in "Permanent Violation" shortly after surfacing.

On this dive had I elected to stay deep enough to go into deco, the obligation would have been very short. My questions and the main reason for this post, was to better understand how others I observed were handling their short deco obligation, and how this would affect a group of divers. I do agree with the comments about having plenty of gas, my wife is about 15% better than me on consumption, so I dive a 100cf tank on the deep dive each day. We both had plenty of gas available for that dive.

Thanks to all who have responded, you have caused me to think and learn which is a very good thing.

 

[FishOutUvH2O]

On this dive had I elected to stay deep enough to go into deco, the obligation would have been very short. My questions and the main reason for this post, was to better understand how others I observed were handling their short deco obligation, and how this would affect a group of divers. I do agree with the comments about having plenty of gas, my wife is about 15% better than me on consumption, so I dive a 100cf tank on the deep dive each day. We both had plenty of gas available for that dive.

Thanks to all who have responded, you have caused me to think and learn which is a very good thing.

On the dives I do, there are always an assortment of different computers with different algorithms. This means that there is always the possibility that some folks computers are going to tell them that they are approaching NDL's sooner than others. It's always handled the same way. Those whose computers are getting close to NDL's ascend a few feet above the group. That's the beauty of having the visibility we do in Cozumel. Ten feet can make a world of difference in NDL times, but you and your buddy can still stay, more or less, with the group. This would be no different for any deco obligation someone might inadvertently get. I personally avoid doing any unplanned deco-dives. I bought the computer to tell me NDL's and I try not to ignore it. But, if you end-up in deco, just remember and plan for the fact that once your computer goes into "deco mode" you're are now under a theoretical "ceiling". Meaning that a direct ascent to the surface without doing the required deco-stops significantly increases your risk of DCS. So, if something goes wrong, you need to have a plan to deal with the problem that factors in that requirement.

I should probably add that if a diver ends-up with deco obligations that would put them underwater longer than the rest of the group, that generally, the rest of the group will surface along the DM's buoy while the DM stays with the diver until their computer clears.

 

[Offroad]

Ten feet can make a world of difference in NDL times, but you and your buddy can still stay, more or less, with the group. I personally avoid doing any unplanned deco-dives.

Yes, it's surprising how different our NDL remaining time displays can be based on the small difference in depth my wife and I will have during the deep portion of a dive. This is with two computers with the same algorithm (Oceanic and Aeris) that read exactly the same depth.

I also agree, the vis while diving at Coz makes it easy for us to stay out of deco if we prefer, while not being separated from the rest of the group. On this dive, when I lost sight of the DM and other divers due to avoiding the last swim through, it was no problem finding them when they had finished it.

 

[FishOutUvH2O]

Offroad- Here's a link to a thread in the Sherwood manufacturers forum. http://www.scubaboard.com/forums/sherwood-scuba/340039-unrealistic-deco-time.html

While it doesn't pertain to Oceanics, It is an interesting discussion on both decompression diving in general and what can go on when a non-deco computer ends-up in deco mode.