what is a decompression dive?

[Matsya]

Actually Mike aren't you and Rawls saying the same thing? He "decided" to ignore the computer based on experience and reasoning and that is what you are recommending one should do rather than blindly follow the computer or allow it to make decisions for you !!

The computer does not go into lock mode to prevent you from doing subsequent dives. It goes into lock mode because its algorithms for calculating NDLs, deco stops etc.are no longer valid since the calculations have now to be made based on the recorded data of previous dive(s) that violated the algortihms. If the intention was to prevent further dives altogether and make that decision for you, the computer would not have the functionality of gauge mode.

 

[Kim]

If the intention was to prevent further dives altogether and make that decision for you, the computer would not have the functionality of gauge mode.

There are MANY boat charters (especially liveaboards!!) where if you surface with a locked computer you don't dive again that day, and depending on your profile maybe longer.
I don't want to put words in Mike's mouth that don't belong there but I think he's making the point of the danger of using a computer and then not actually doing what it says because you think you know better. If you DID know better...why were you using a computer to begin with?
For new divers theres obviously a LOT wrong with this and I can assure anyone out there reading along here and wondering what's going on - ignoring your computer is a potentially extremely dangerous practice.

 

[MikeFerrara]

Actually Mike aren't you and Rawls saying the same thing? He "decided" to ignore the computer based on experience and reasoning and that is what you are recommending one should do rather than blindly follow the computer or allow it to make decisions for you !!

I don't think so. I don't use a computer because I plan my decompression, including contingincies, by other means. It sounds to me like Rawls stoped following his computer because he didn't like what it said and switched to following some one elses computer. It's too early in the morning for me to know just how to put it into words but I don't think it's the same thing. If nothing else, when in doubt, follow your training. What are divers taught to do given the outputs of multiple computers? I think they're taught to follow the more conservative computer, aren't they?

The computer does not go into lock mode to prevent you from doing subsequent dives. It goes into lock mode because its algorithms for calculating NDLs, deco stops etc.are no longer valid since the calculations have now to be made based on the recorded data of previous dive(s) that violated the algortihms. If the intention was to prevent further dives altogether and make that decision for you, the computer would not have the functionality of gauge mode.

Really? This might be a little hard to discuss without using a specific computer and a specific dive profile but exactly how does a recreational diver doing no-stop dives keep diving after their computer locks up? Aren't they likely to be off their no-stop tables? I'm not sure what you get when you overlay a haldanian model with elements of a bubble model as I think some computers do now but, in the case of a haldanian type model, I don't see why the computer can't keep crunching the numbers. The computers that I've used do just that. I think the lockup modes are absolutely intended to keep the diver out of the water if they were relying on the computer for decompression information. Look in the book for your computer. What does it suggest you do in the case of an error that locks up the computer?

Back on the subject of doing a disservice to new divers, I'm not telling any one that they shouldn't plan their decompression but there are ways other than computers. I also wouldn't tell some one who is using a computer not to follow it. If a computer is your choice for decompression information then you should probably follow it.

What else would I say to a new diver? A dive team made up of divers who are diving different models is as wacky a thing as I can imagine unless the planned dive is within the limits of all the computers. The whole team needs to plan on the same ascent schedule because they should ascend together. This seems like a complete no-brainer. If one diver has a problem during ascent that requires that they go to some contingincy plan then the rest of the team is with him. In other words lacking any decompression information besides the outputs of the computers, I think that Rawls should have followed his compter and his buddies should have stayed with him...NOT the other way around. Maybe his computer was off in left field but he didn't think so when he baught it or when he started the dive. He also didn't state the exact nature of the error but I would think it needs to be fairly significant to shut the computer down for 36 hours. No? If his computer is just that incredibly conservative, refer to point one...a dive team made up of divers using different models makes no sense at all unless they plan on diving a profile that they know to be within the limits of ALL the computers! This dive clearly didn't fit that description.

This was a training dive? I'd love to hear the instructors story too.

 

[Charlie99]

.... in the case of a haldanian type model, I don't see why the computer can't keep crunching the numbers. The computers that I've used do just that. I think the lockup modes are absolutely intended to keep the diver out of the water if they were relying on the computer for decompression information.

I agree with your comments about not just arbitrarily, in the middle of a dive, deciding to ignore the computer because you feel like continuing your dive. That's a LOT different than planning the dive with some other means and following that plan.

The old "plan your dive, dive your plan" is a pretty broad and useful rule.

I do however take issue with your "the computer should just keep crunching numbers" comment. If you have spent signficant time above the deco ceiling, bubble formation in tissues is a significant possibility. At that point the haldane/dissolved gas model isn't valid. Or to put it more crudely, once the computer decides that you have good possibility of being bent, it doesn't know how to calculate decompression for future dives.

My assumption on the rationale behind going to gauge mode is that, in a situation where a diver has violated ceiling depths for some reason, there may be some sort of emergency taking place, and the diver may choose to go back down to deal with it. Although the computer can no longer provide valid decompression info, at least it can provide depth and time info.

 

[rawls]

If a diver needs some one else to make their decisions they should bring their mother.

Mike...I think this is what you wrote. When the computer put me into deco, me, my instructor and the photographer all began to surface at the same time. Both of them had 10 minutes of dive time left on their computers. I nevertheless did the stop and my instructor stayed with me. Even after the stop it still locked me out and I don't know quite why. When we surfaced we first checked my computer and it was set to the correct EAN. The thing my instructor found however was my computer was set very conservatively. So I had an already conservative computer which was set even more conservatively. We sat down at that point and had a discussion and decided to do the next dive, and yes, using their computers and mine in gauge. Was it the perfect way to do things, no, but we spent alot of time during the surface interval discussing our plan. My instructor has 20 plus years of tec diving and has an instructor rating in everything from open water to rebreather. So I felt comfortable when he felt ok about doing the next dive the way we planned. Since I reset the computer to a less conservative mode it has put me alot more closely in line with his, although it is still somewhat more conservative. I have a Vyper and Jon has a Uwatec. Don't know the model. All this stuff had absolutely nothing to do with "not liking what my computer was telling me". I, by no means, am trying to second guess what you were saying, but I interpreted it as saying I basically disregarded what the computer told me and that's simply not true. When I made the decision to do the dive...even without calling mom...It was done after review and planning, just as I'm sure you do...Not being tart...I'm sure you plan your dives well. But I plan mine too. I consider myself a very safe diver. As far as the disservice to new divers...please refer to your above quote...

I think he's making the point of the danger of using a computer and then not actually doing what it says because you think you know better. If you DID know better...why were you using a computer to begin with?

Kim...Once again...I did not "ignore" my computer. If I had ignored it then I would not have let my instructor know anything about what was going on. I don't think that falls into the category of "ignore". If he had said we don't do the dive then I would by no means have done the dive. I made the decision to do the dive because I have alot of respect and trust in his experience and in the fact that we talked about it at length. Mike does his dives without a computer and I am sure he is very careful planning his dives. I'm not saying there is one thing wrong with that. He is not the only diver who uses 2 bottom timers on their dives. I am just assuming he uses 2. I understand your point and totally agree with it, but this wasn't the case on my decision to do the second dive. I by no means ignored my computer. The only thing I ignored was not making this point earlier and for that I apologize....

One more thing Kim...If you are going to take a stab at me by that "because you think you know better" quip then I would appreciate you look at the above quote and square the playing field. First of all you have absolutely no idea about what I am thinking. But if you think that you do know what I am thinking... that you have the capacity to read my mind then go ahead and take that stab...But play fair ok...

 

[String]

I'm also not sure but I've also heard similar stuff about Suuntos (I have a Vyper). I only ever pushed it into a couple of minutes deco on a last dive of the day once. The next morning it was fine - I've got no idea if it would have let me do a night dive the evening before!

Nope it'll work just as normal provided stops arent missed. I do a fair amount of deco diving and see my vyper in deco quite a lot. Dont error it by missing stops/rapid ascents and it'll work just fine.

Last week forgot to set it to gauge mode, did a dive requiring (on the vyper not the tables i used) 30 mins of stops. Sat out those stops, surfaced, computer quite happy for second dive a bit later.

Vyper,Vytec,Mosquito,Stinger,Cobra all the same. No decent dive computer should lock out for going into deco if the stops are completed.

Actually - first it showed me a couple of minutes deco but by the time I'd (slowly) ascended to my ceiling it immediately cleared. It was all very 'on the edge'.

Very common. As soon as you ascend above a certain depth off gassing begins. If its not many stops and ascent is slow enough its common for computers to clear before reaching the first stop depth. Also the Suuntos build in an optional 3 min safety stop on their ascent time so its common to jump from 4 mins stops to no mandatory stops on the way up.

Edit:- although the reverse is true, try doing a pyle stop/deep stop with a suunto still in computer mode and watch it rack up the shallow stops you need to complete.....

 

[Kim]

Kim...Once again...I did not "ignore" my computer...........

One more thing Kim...If you are going to take a stab at me by that "because you think you know better" quip ...

Your original post seemed to suggest something completely different from your explanation now. I'm not taking a stab at you, just what you appeared to be saying. If new divers get the impression they can ignore their own computers and safely follow their buddies computer instead part way through a dive I can't ignore it. That seemed to be your message, and you yourself say that you weren't clear enough - hence the much longer detailed explanation now.

In this case I chose to ignore it because I was diving with 2 divers who were with me at the same depths for the same time, so I knew I probably wasn't in deco.
(quote underlines by Kim).

doesn't mention immediately surfacing or planning further dives, and does suggest that you didn't believe what your computer was saying and ignored it.

 

[rawls]

Your original post seemed to suggest something completely different from your explanation now. I'm not taking a stab at you, just what you appeared to be saying. If new divers get the impression they can ignore their own computers and safely follow their buddies computer instead part way through a dive I can't ignore it. That seemed to be your message, and you yourself say that you weren't clear enough - hence the much longer detailed explanation now.

Kim...You are absolutely right. I didn't clarify enough and I admit it. But I also think it's only fair to not take a jab at one poster and not make reference to a remark that if a diver cannot make a decision for themselves then they should take their mother. But that's just my feelings and they may not be yours.

 

[Kim]

Kim...You are absolutely right. I didn't clarify enough and I admit it. But I also think it's only fair to not take a jab at one poster and not make reference to a remark that if a diver cannot make a decision for themselves then they should take their mother. But that's just my feelings and they may not be yours.

Well, to be fair I believe Mike and I were simply responding to your original post which seemed to suggest doing something quite dangerous. (By the way - I never mentioned anyones Mother! )
Now that you have clarified it I'm not arguing with you anymore....

Still - without Mike and my own comments I strongly suspect that that clarification might not have been forthcoming and the wrong impression left. When it comes to safety and advocacy of doing something potentially dangerous it really does become important to refute what is said, and give a clear reason as to why what was said was so wrong. THIS is for the benefit of our newer divers who might read threads such as this. We don't want ANYONE getting into trouble following advice that they've read and think they understand from the board....even more so if the original poster didn't actually say what they meant!

 

[rawls]

Now that you have clarified it I'm not arguing with you anymore....

Agreed...I'm tired of arguing about it too Thanks for the input...