Can you dive again after a minor Deco dive?

[Spectre]

ScubaAaron once bubbled...
My computer is rather conservative and at 90' I get 17 minutes NDL time. My buddy's computer gives him 25 (as does the PADI table I believe). So if I go to 90' for 23 minutes I'm in DECO mode. It does not go blank and only show depth, it apparently will show me what depth to go to and how long to stay until I'm "out" of DECO. Then I can surface safely.

Am I pushing the envelope too far?

To answer your question here.. I would say yes. Given what I'm assuming your training level is, you should probably be sticking to the most conservative computer, or go back to tables and dive on those. But stay within the NDL until you have the training and underwater comfort necessary for a ceiling.

BTW: The computer display most likely isn't telling you the depth to go to. It's telling you the ceiling. The first mistake many OW divers make when kicking into deco on their computers is to bolt to that ceiling. You are much better off doing a slow and steady ascent.

Without deco training, you are better off sticking with your training and not pushing things. There is a lot more to overhead environment diving than just avoiding DCS.. there is gas management, there is dealing with emergencies at depth, and of course there is the issue of your buddy being on the same page as you with your dive plan.

You should know how you are getting out of the water before you get in the water, not figuring it out at depth. You should be planning your dive and diving that plan... your computer is best served as an in-water backup to make sure what you planned jives with the algorithm. Don't get out when your computer tells you... get out when you plan to get out, and make sure your computer is happy before you get out.

A good example of why you don't want to blindly trust your computer is the Uwatec problem that they just recently had a recall on... .where the offgassing on the surface interval was treated as using the gas on your dive, not air. So if you were diving 32%, it assumed you were on 32% on your surface interval. Blindly following your computer can definately get you into trouble...

Don't push yourself too far too fast, get the training -and- experience you need at each level before getting yourself, or more importantly, your buddy, in trouble.

So... in a nutshell. Dive the most conservative profile in your team, and stick within the experience, training and comfort levels of the team. If you aren't familiar with decompression procedures, you're better off sticking to your training, which depending on your certification agency is 6 hours of SI if you come within one pressure group of the NDL limit, and 24 hours of SI if you exceed the NDL limit.

 

[Don Burke]

Deco diving with different computers brings in all kinds of issues. Some may give you more time on the first dive and then cut you very short on repetitive dives.

The simulator on my old Oceanic will cut you pretty short on a dive after a deco dive. It will also spring a pretty long stop on you if you go beyond the no-stop limit on two consecutive dives.

 

[DA Aquamaster]

I agree you should not be doing deco without formal training. i I would suggest that if you are intentionally doing deco, you are doing "technical" diving whether you intend to be tech diving or not as you are in an overhead environment and outside the bounds of normal recreational diving.

You need to have a fully redundant air supply adequate to support you from max depth depth through your normal ascent and deco stops plus some fudge factor and this means a pony of at least 19 cu ft. if you have good air consumption. 30 cu ft is better and a minimum if you are a hoover. A properly configured set of doubles is far superior and highly recommended.

I am middle of the road on using computers.

Some computers offer a limited deco capability designed to get you to the surface when you mildly and unintentionally exceed the no deco limits. For intentional deco diving even when you are only planning short 10 ft stops, I would avoid them at all costs.

They will get you in trouble in a hurry in planned deco diving as they do not support stops much deeper than 10 or 20 feet and will in most cases lock up on you if you go out of range with them. A small delay of a fe minutes at depth (for example getting tangled just before your planned ascent time) can result in them going out of range, leaving you guessing as to your depth, time and deco schedule. They also have extremely limited planning modes that preclude proper planning for a safely executed second deco dive.

Some higher end computers offer a greatly extended range in terms of both depth and deco time and can accomodate deco stops to depths of 70 ft or greater without locking up on you and the better ones will go into gauge mode rather than lock you out if they do go out of range.

The better computers also offer simulation and planning modes that will allow you to pre plan your initial dive and repetetive dives just like a table. If all of these features are present I have no problem with using the computer for deco diving as long as appropriate precautions are taken including adequate contingency planning for a minimum of the the next two greater times and depths. But to do this properly still requires adequate training in using and understanding tables and in deco diving procedures.

You need to assume you computer will die on you during each and every dive and use a slate or similar low tech device to record contingency plans for the relevent times, depths and deco schedules you may encounter on the dive. A watch and backup depth gauge are also required equipment to complete the dive safely when your computer goes dead.

I also agree that every dive is a deco dive. Being a few minutes over the NDL is no big deal (and with Navy tables would probably not even have been considered a deco dive anyway) as long as the ascent rate is slow and controlled and the required deco stop is made. But the lack of planning or mistakes that got you into that situation are a BIG deal and need to be corrected.

I do a lot of deco diving including repetetive deco diving and with proper training and equipment am not overly concerned or overly at risk. But nothing makes me cringe more than to see a single tank diver with no redundant air supply or an inadequate redundant air supply doing a planned deco stop. Sooner or later things will go wrong, the odds will catch up with them and they are going to get bent.

 

[100days-a-year]

Actually it's pretty easy to get into deco mode on any computer with a single 80.Almost every time i spearfish deeper than 90' my NDL is the factor bringing me up.As every dive is a deco dive,ascent procedures and stops shouldn't be foreign but many times students aren't made aware enough about this.For some ideas on how stops and ascent rates work on gas loads I suggest the GAP program as it shows a graphic representation of tissue group gas loads.I don't use it for diving since Vplanner but it is a great learning tool.If you plan to continue this type of diving a intro-level tech class could really benefit you.

 

[Karl_in_Calif]

cornfed once bubbled...


There is nothing strange about this at all.

Different computers, different algorithms, differerent answers.

PADI's tables don't agree with SSI's tables, so why would you expect two different computers to agree?

PADI's tables were specifically designed with -0- deco as a basic premise. Different story. Bad analogy.

SSI and NAUI(old) tables are all variations of USN. But these are tables not computer algorithms. Different story. Bad analogy.

You are trying to analogize to different computers with different algorithms.

I would not expect computer algorithms to vary that much from each other on the NDL side. Maybe a minute or two. I would not expect a big difference. Maybe there is?

I have only dived with my Suunto Vyper dive computer, and I consider all other dive computers as inferior.

Having stipulated that, I would not stay longer than my Suunto told me I could stay at a given depth on an NDL dive, even though I am acutely aware (acutely, CornFed, very acutely) that USN tables are very, very generous. Nor because of anybody else's NDL computer as well.

 

[DA Aquamaster]

The algorithm in my old Scubapro computer was very conservative in the middle depth range around 80 ft, and offerred bottom times in that range that were drastically shorter than everything else in the water. A pain in the butt when diving with buddies in that range, but I never skipped a stop just because their computer said it was not required - that is a really bad idea.

My current Wisdom computer offers about 2-3 minutes more bottom time at depths in the 100 to 130 ft range than my older pelagic made computer and is actually more generous than the US Navy tables below 130 ft.

There is also a difference in depth readings between my old and new computers that is fairly linear with a deviation of about 1 ft per each 60 ft of depth resulting in a 2 ft difference at 120 ft. Both are within their expected 1% accuracy but just at different ends of the acceptable deviation curve.

A 1 to 2 ft difference in computers held side by side at depth is pretty normal and not very significant. But I have seen identical computers with a 5 ft difference at depth (one was screwed and needed to be replaced). A five foot difference throughout most of a deep dive can mean a fairly significant difference in terms of remaining bottom time or deco required even with identical algorithms.

 

[cornfed]

Karl_in_Calif once bubbled...

PADI's tables were specifically designed with -0- deco as a basic premise. Different story. Bad analogy.

SSI and NAUI(old) tables are all variations of USN.

Would you please explain the difference in table design. What is the underlying premise of the PADI/DSAT tables that make them so different then the modified Navy tables used by others? How does the design of one set of NDL tables differ from that of another?

But these are tables not computer algorithms. Different story. Bad analogy.

Would you please explain how table design is do different then computer algorithms. What is it about each that makes them so different?

You are trying to analogize to different computers with different algorithms.

Good, I was afraid you weren't paying attention.

I would not expect computer algorithms to vary that much from each other on the NDL side. Maybe a minute or two. I would not expect a big difference.

I retract my last statement.

I have only dived with my Suunto Vyper dive computer, and I consider all other dive computers as inferior.

Please explain why, in your opinion, you consider all computers to be inferior to the the Suunto Vyper. What is it that makes the Vyper so much better then other computers. Why is it better then the Suunto Cobra? Why is it better then the Uwatecs, Oceanics, Cochrans, etc.?

You have made several comments which I believe warrant further explanation. I would appericate it you would justify your statements.

 

[Karl_in_Calif]

cornfed once bubbled...


Would you please explain the difference in table design. What is the underlying premise of the PADI/DSAT tables that make them so different then the modified Navy tables used by others?

You need to study PADI's RDP to find out the answer to this question. If you buy PADI's Encyclopoedia of Recreational Diving it will answer your questions about the RDP. PADI is very proud of the RDP, however you must avoid deco for it to be valid for your profiles.

OR you need a PADI OWSI who is qualified to teach you. I am not a PADI OWSI, therefore I am not qualified to provide your request. Youre on your own.

 

[Karl_in_Calif]

cornfed once bubbled...
Please explain why, in your opinion, you consider all computers to be inferior to the the Suunto Vyper. What is it that makes the Vyper so much better then other computers. Why is it better then the Suunto Cobra? Why is it better then the Uwatecs, Oceanics, Cochrans, etc.?

Cobra is a good computer too. No disagreement there.

Uwatec and Cochrans have been subject to recalls.

Anything with Oceanic printed on it I simply do not buy. This is the low cost end of scuba equipment specifically marketed to the rental departments and to divers on a strict budget.

 

[cornfed]

Karl_in_Calif once bubbled...

You need to study PADI's RDP to find out the answer to this question. If you buy PADI's Encyclopoedia of Recreational Diving it will answer your questions about the RDP. PADI is very proud of the RDP, however you must avoid deco for it to be valid for your profiles.

OR you need a PADI OWSI who is qualified to teach you. I am not a PADI OWSI, therefore I am not qualified to provide your request. Youre on your own.

How is studying the tables (PADI’s RDP) going to tell me anything about how they were designed? If I buy the PADI Encyclopedia will learn how to read them. I will learn nothing about how they differ from other tables. Saying you need to stay out of deco for non-deco tables to be valid is like saying you have to breath nitrox for nitrox tables to be valid.

Karl, you haven’t answered my question. In fact you’re so far off I’m not even sure you understand what the question is. You claimed that recreational NDL tables are so different in design that they can’t be compared to diving the algorithms used in computers. Furthermore, you claimed that some tables are so different in design that they can’t even be compared to other tables. I would like you at defend these claims.

I would also like you to explain how the “USN tables are very, very generous”.

All I want is for you to provide valid support for the claims you make. You haven't done that. You haven't even come close.