Liberal vs Conservative

[eponym]

I definitely do not intend to play chicken with DCS. I just want to understand the pros and cons of the differences among these computers. All the responses have been great.
Do you all rely on the computer for NDL, or do you plan your dive, dive your plan and refer to your computer for reference?
I very rarely have a square profile so I would think general planning would be in order, but would use the computer for more guidance through out the dive.

I dive with a Suunto Vyper. The NDL times it allows on air seem very comparable to table limits, if you're holding a square profile. Obviously the credit you get for non-square profiles adds up to a good deal more bottom time than any (?) recreational dive table will give you.

When I dive Nitrox, the Vyper seems a bit more conservative on non-deco times than using equivalent air depth with my tables. It's also quite a bit more agressive in assigning oxygen toxicity units while diving nitrox. I asked Suunto about that and they replied that this is a recreational diving computer and they want it to be conservative in this regard.

I often don't do pre-dive planning on familiar spots with hard bottoms, unless I'm diving with a new guy--then it's nice to have some parameters agreed on. So a lot of time I'm just keeping track of air and on a single tank it's rare for me to run up against time limits on the computer. But these are relatively shallow dives, usually not much chance of getting below sixty feet.

I'd say the biggest factor in choosing a computer might be usability. How easy is it for you to navigate the menus, set and check the options, read the display, and interpret what it's telling you? If you go into deco obligation, does the display make sense or will seeing "STOP" displayed make you stop in your tracks? (On the Vyper, it means you will have an obligation to stop, later in your ascent.) How clear is the ceiling & floor information when you reach that point?

Please: I am not advising anyone to use a recreational dive computer to do decompression dives. I wouldn't even do that to myself. The functions and procedures are built into the machines, however, and should you need to follow them it's important that you be familiar with them and able to respond correctly.

Fin on,
Bryan

 

[DEEPLOU]

Pick up this month's ScubaDiving Magazine. They answer this exact question. They even review your selections. It includes the bottom time allowed on a variety of dive profiles. It is suprising how different some of them are.

Most of the time I hit the water w/ 3 computers, Aeris Atmos 2, Dive Rite Duo, and Suunto Viper.
For calcuations they are identical to Aeris Elite, Tusa Hunter, and Suunto Geko that were reviewed.

This article confirmed what I have seen on multiple dives.
The article was not that clear to indicate that the Tusa was a 2 gas computer that allows you to switch to a deco gas.
Since most of my dives are in the deco zone, I run a schedule on D Plan and follow it, but at final stop, wait to clear the DR Duo.
Some profiles the Aeris will clear within a minute or two of the Duo (even though it is not calculating 100% O2 at 20 ft), the Viper usually tells me I have about another half hour of hang time.
For successive dives the Viper serves as a bottom timer only.

As aggressive as the Aeris is, I have not read of it being sued due to it getting divers bent on regular (or not) basis.

I am aware that Uwatec is involved in a law suit. But I understand part of that is error in its calculations and a coverup of its knowledge of the situation.

 

[Uncle Pug]

rlowe desires, "as MUCH safe bottom time as possible... as much SAFE bottom time as possible"

outlawaggie reviewing a ScubaDiving Magazine (gaaakkkffffphttt) article notices "It is suprising how different some of them are."

RichLockyer reports, "DCS incidents are reported to have increased in recent years, and a lot of te blame is being put on people getting right up against NDL and then riding it all the way up. Of course, at 30-50ft, the computer "relaxes" and shows over an hour of available NDL, so the diver relaxes and it not as attentive to his safety stop and ascent rate."

pasley notes, "There are so many variables, age, hydration, fatigue etc. In my mind, diving with out getting bent is more important than pushing it to the edge and diving for 5 extra minutes. Remember DCS is not and exact science."

Folks.... not only is decompression an inexact science, the pertinent variables are much more numerous than any dive computer can accept as input and take into account. The manufactures of dive computers know this and build in liability driven conservation factors to one degree or another.

You can't get maximum safe bottom time using a dive computer!

 

[DA Aquamaster]

UP is exactly right. The last word in conservatisim has to be yours. If a particular dive has been harder working than usual, or colder than usual, or you don't feel as good as you should diving to your computers limits, or it is your umpteenth dive of the day, or your umpteenth diving day in a row, or (insert variable here), etc, etc, then you need to take it upon your self to apply whatever conservative adjustment you feel the situation dictates. Erring on the side of caution is always advised as computers just crunch numbers in theoretical mathematical models with little or no consideration of all the variables that affect divers in the real world. Anyone who puts all their faith in a dive computer is a DCS case waiting to happen.

Personally I like the convenience and download/data capability of a dive computer but I also concurrently track my dives and surface intervals throughout the day with either DPlan or Palm VPM on my PDA for a few reasons.

1) If the dive computer quits I want to know where I am in terms of deco obligation for the dive and I want a deco schedule taped to a fin where I can use it if needed, (and where it can be used for the deco anyway as the deep stops are a more conservative approach). As an added benefit even with a computer failure I can keep right on diving that day as I still know where I am regarding N2 loading.

2) Both DPlan's bubble gradient model and Palm VPM incorporate deeper stops and are in all cases more conservative than my dive computer's model. The dive computer also seems to be able to live with the deep stop ascent profile with only a few extra minutes needed at 10 ft to keep the computer happy and a few extra minutes at 10 ft is just a bit more conservatism - sort of a saftey stop after the deco stops.

3) By always keeping tabs with Dplan or Palm VPM and observing the results, I get a very intuitive feel over time on how much deco will be needed in a particular situation. And over time I have developed a very good general idea of what the ascent curve should look like. So in the end my brain is able to be both the backup and the accuracy check for everything else. That is something that never really developed to the same degree when I relied soley on the advice of a dive computer.

In my opinon, if you are concerned about saftey and getting the most bottom time for an acceptable level of risk, put less thought into finding the ideal computer and more thought into learning about deco theory and models.

 

[rlowe]

My conclusion is that I need to put more emphasis on planning the dive and keeping track the good ole fashion way. I have not done a lot of seriously challenging dives so to date, its been relatively easy to do. And since I dont have a computer it's all I have. That said, my dives are rarely square, so I might spend a little time at 70 ft and then some time at 50 and so forth. I just thought a computer might help safely extend the dive time beyond the basic table (square profile).

More education for multilevel planning on the way for me.

Randy

 

[Mark Vlahos]

My conclusion is that I need to put more emphasis on planning the dive and keeping track the good ole fashion way. I have not done a lot of seriously challenging dives so to date, its been relatively easy to do. And since I dont have a computer it's all I have. That said, my dives are rarely square, so I might spend a little time at 70 ft and then some time at 50 and so forth. I just thought a computer might help safely extend the dive time beyond the basic table (square profile).

More education for multilevel planning on the way for me.

Randy

Absolutely, multilevel dive training is great. But remember, a dive computer is just a tool. It can be one of the many tools that you bring to each dive. A carpenter can not build a desk with only a hammer, he needs many tools to turn the raw materials into the finished porduct. For a diver, training is an important tool.

I took the PADI Advanced Open Water course and found it helpful, but I learned LOTS more in my Decompression class. I found the Decompression class to be more like what I expected the AOW course to be. That being said I think the Deco class has an expectation of around 150 dives under your belt, so you may not be ready yet.

Mark Vlahos

 

[mkgriesinger]

Hi All,
I never hear of people getting Decompression sickness when using a dive computer. I have tried searching articles and forums . So i guess the questions is, has anyone heard of getting sick while using ANY (Liberal or Conservative) dive computer that hasn't "malfunctioned?"
Thanks

 

[Hatul]

Hi All,
I never hear of people getting Decompression sickness when using a dive computer. I have tried searching articles and forums . So i guess the questions is, has anyone heard of getting sick while using ANY (Liberal or Conservative) dive computer that hasn't "malfunctioned?"
Thanks

There was just such a report in the last DAN magazine and I read other reports as well. These are divers who followed the advice of their computers and got bent anyway. In my mind that's an argument in favor of conservative algorithm.

Adam

 

[jd950]

You are reviving a thread from 6 years ago. If you dive, you can get bent. Computer, no computer, liberal, conservative, it doesn't matter. Sometimes there is no apparent "reason."

I know you said you searched, but search through the accidents and incidents and dive medicine forums for extensive discussions on this and if you are a member of DAN you can search their databases for a number of articles on the topic. Look for terms like "bent" "undeserved" "algorithm" "chamber."

The short answer is yes, people get bent while using computers. Not that many people get bent at all and when they do the details are not always clear, so you will have a hard time finding any useful stats. Computers don't know your age, health, hydration level, exertion level (usually), or how rested you are or your luck, and all of those can be factors.

You will not find anything that links any particular brand of computer or algorithm to an increased risk. Such a computer would fail in the marketplace and all manufacturers try to utilize an algorithm that they believe will not damage their customers.

The computers don't usually malfunction, at least not in a way that causes injury but divers often do, by taking their computer to its limit and beyond, failing to account for their own individual health, ascending too fast, etc. DAN's Alert Diver runs an article every issue detailing some dive accident from their files.

Hope this helps.

 

[fnfalman]

Want to have "safe" bottom time?

Don't go near No Decompression Limit. It's that simple. When your nitrogen loading bar start to get up towards the higher end, end your dive before you hit NDL.