Must I abort if computer fails?

[Hatul]

Dive computers are so inexpensive now, you can pick up a backup for $200.

Adam

 

[Reg Braithwaite]

The following plans are followed by thousands and thousands of divers all over the world. I guess they aren't adequate. You would be doing a great service to these people if you can tell what they should be doing instead so that these directions can be given to them.

I certainly never suggested that anything is inadequate. I was simply asking if a diver getting into the water without some sort of idea how deep they will go, how long they will stay there, and what implications this have for their ascent/deco is considered a dive plan.

You seem to be suggesting that it is a dive plan, and under many circumstances an adequate dive plan. I have no argument with this, however I do want to be clear so that if you call that a dive plan, I will use a different phrase for discussing a plan where you have a known estimated NDL in advance.

I believe that to be relevant to this thread because if you have an estimated depth and time in advance, you need not abort the dive when your computer fails. I just wanted to get on the same page about terminology with you.

 

[halocline]

The reason that so many recreational dives, including hundreds of my own, can be done without planning specific depths for specific times is that the depth/time involved is well below any NDL issues. But doing such a dive knowingly does not mean "no plan". It just means that the diver knows beyond any doubt that his/her profile will not go near any decompression limits.

That's quite a bit different than "riding the computer" which is what Richard originally was talking about.

 

[Rhone Man]

I dive with two computers. Has two advantages:-
(1) you have a backup in the event of failure
(2) I don't mind squeezing every last drop out of the battery because of (1)

 

[rstofer]

the tables are not Accurate, the computer does not take into account your particular body, and there are many algorithms that give different answers to the same question "how long can I stay at this depth?"

I think everyone is willing to concede that you can't dive NDLs all day whether by computer or tables without increasing risk.

However, millions and millions of dives have been made with tables and, as the tables have gotten more conservative over time, the incidence of DCS has fallen. Are they perfect? No! But neither are computers.

In fact, if a diver rides the NDL of a computer, they are probably at a much higher risk of DCS than the table diver who treats his multi-level dives as a square profile.

I have a computer simply to deal with the nitrox issues. Accumulating O2 over a 24 hour period is more than I want to keep up with. But I have always been satisfied to dive with tables.

Richard

 

[boulderjohn]

Let's start wit this. Here was the challenge:

I'm confused. Do you consider "I will get in the water and dive until I reach some sort of gas limit or until my computer tells me I have reached my NDL" a dive plan?

Just a few observations as I see them:

A computer isn't relevant in this situation, just an SPG.

See above. ""I will get in the water and dive until I reach some sort of gas limit..." A lot of people use SPGs to tell if they have reached a gas limit. What's your point? I asked you to tell what is wrong with the plan and how it could be improved. I miss where you do that here.

Just relying on a computer, they won't know what their NDL is until they hit it. If a computer dies, all they can do is abort this and any subsequent dives. Planning based on the gas and wreck depth before the dive, everyone will know before the dive what time to call the dive.

Have you read this thread? Why won't they know their NDLs before the dive? Why must they abort? Note, too, that I never said they needed to do this with a computer. That was your imposition. Again, note Reg's original challenge wording.

First, without planning ahead or having some knowledge of basic table profiles, how do you know 15 minutes at 80ft is NDL? Second, once you're at 20ft, are you likely to hit an NDL?

Who said 15 minutes at 80 feet was NDL? It isn't anywhere I know. Who said they didn't know anything about the tables and NDLs? If you are going to add extra problems that were not in my statement, why not make them deaf and blind as well? I just gave an example of people choosing to dive a specific depth for a specific time. I asked you to tell what was wrong with the plan and what you would do differently. You did not do that.

Same as 2 & 3.

Exactly.

If relying on a computer's real-time output, how will this plan account for sufficient reserves to cover the overstay? If two divers have overstayed and one goes OOA?

You added another condition not in the original: All the divers are blithering idiots who are not looking at their gauges. "OK, we are 15 minutes into the dive. The last time we checked, everyone had plenty of gas. We just saw an absolutely spectacular site that I would love to explore for 2 more minutes, but we can't because it is not in our plan. One of you might go from a 2/3 full tank to OOA in the next minute, and I don't want to be responsible."

So you would require a plan that calls for specific times at specific depths for the entire multi-level experience, no matter what, is that what you are saying?

Last May I was diving on the big island of Hawaii. We started our dive, planning to go to a specific starting location at a specific depth, but as we descended we saw in the distance that a Manta Ray was being cleaned by some wrasse. We moved to that location. The ray eventually moved away, and we were about the same when an eagle ray came in to take its place. We stayed to watch that a couple of minutes, checked our gauges, and moved on. Then we moved up the reef to a shallower level where we encountered something else about as interesting. Then we moved on up and finished our dive on the top of the reef. It was an absolutely spectacular dive.

If you had been leading another group the same day, you would have seen none of the above. "Hey, there's a manta ray over there!" "Sorry, that precise depth and time is not in our plan." Look, an eagle ray is coming!" "No, got to move on. I'd love to watch, but we didn't plan for that." OK, you would have followed the plan, but I think a lot of other people would have preferred a plan that allows for the unexpected and adds a minute here or there.

I believe it all depends upon the situation. If I am doing a deep decompression dive, I will plan everything very carefully. I will check my air consumption rate against the planned depths and times to make sure I will have enough gas. I am trained in all of these planning details, and I will use that training. On the other hand, put me on a multilevel reef like I described above, and I will rely on simple turn pressures and the like. I will look at my gauge and I will explore what is there.

 

[Reg Braithwaite]

put me on a multilevel reef like I described above, I will rely on simple turn pressures and the like. I will look at my gauge and I will explore what is there.

Well everything seems straightforward. I said somewhat earlier that if you had a dive plan laid out in advance, there was no need to abort the dive should your computer fail, you could continue based on your plan.

You said that a plan could be based on simple turn pressures. It sounds like if you have a plan based on turn pressure and your computer failed, you could finish the dive when indicated by the turn pressure.

Are we in "Violent Agreement?"

 

[TSandM]

It's funny -- on a deep decompression dive, if we ran into the kinds of things you described (mantas and eagle rays) we'd have the freedom to adjust the depth or bottom time, or both, so long as we remained within the outside parameters of deco and gas that we had set for ourselves at the outset. That's the beauty of RD -- consult the team, and you can change things.

I have changed dive plans, but it requires consultation with the entire team to do it, to make sure everyone is comfortable with the change.

 

[caymaniac]

I would abort the dive if my computer failed. I had a computer failure once about 8 yrs. ago, while on day 2 of a dive trip on Cayman Brac. At 110 ft. in a chute my computer crapped out, my wife had gauges but who could say how long I had been at what depth. I signaled to abort the dive and took the next day off as I had a full ten days on the island. I took my computer batteries out and used a pencil eraser to clean the contacts on the computer, I dove the rest of the week without incident.

I now have a redundant computer in my BC pocket.

 

[Mr Carcharodon]

That's the beauty of RD -- consult the team, and you can change things.

.

But ratio deco gives you a framework within which to replan the dive. Many of the people here do not have that framework and little or no situational awareness that lets them know how close to the limits they are at any point in the dive. Additionally they typically have no plan of what to do if they suspect they have run over their NDLs. For that group of people terminating a dive is likely the best choice.


RD, especially within recreational limits, is a simpler tool than conventional tables, and simpler that working with a team that has multiple computers with multiple answers. Hopefully more people will learn about it over time.