Dive Computers - Pros and Cons

[Deep Blue]

I posted the following as an attachment to another post, but looking at it, I think it would make a great start for a discussion. So here we go.....

Baker's Dozen for not using a Dive Computer By Jarrod Jablonski

1) Dive computers tend to induce significant levels of diver dependence,
eliminating the awareness so common and essential to all diving but
particularly obvious when diving tables
2) Dive computers do not allow proper planning as divers can't properly
"study" the impact of various mixture and decompression choices.
3) Dive computers are of very limited educational benefit as they do not
induce questioning, or proper planning discussions as can be found with
tables and most particularly with deco programs
4) Dive computer programmers often play games with computational process
so that they can take insulate themselves from the risk of taking
largely square profile data and utilizing it on a multilevel dive. These
games tend to result in odd and often ridiculous levels of conservation.
5) Dive computers are expensive and in some cases leave divers with
limited resources carrying equipment that is of far less benefit than
other equipment that may have been purchased.
6) Dive computers significantly limit the likelihood that divers will
track their residual nitrogen groups.
7) Dive computers do not allow for Helium diving in any formats but the
bulkiest and most questionable format.
8) Dive computers will often generate longer decompressions than could
be figured by an astute, well-educated diver with experience.
9) Dive computers often create confusion by giving the user too much
useless information, sometimes even obscuring depth and time in favor of
blinking CNS and/or deco limitations.
10) Dive computers can become very difficult to properly if a deco stop
has been violated. Some computers lock up completely while others just
beep or generate erroneous and distracting information. Divers using
mixed gasses are likely to often violate computer profiles.
11) Dive computers do not allow for the educated diver to properly
modify their decompression to account for advancing knowledge such as
the use of deeper stops in a decompression profile.
12) Dive computers do not offer divers as much flexibility in the
generation of profiles with varying conservation. For example the right
mix would allow 100 min at 60 vs. 60 at 60 but I might prefer to do one
or the other and indeed might like a compromise. Computers confuse this
issue by not providing divers with the proper information.
13) Dive computers users often ignore table proficiency and therefore do
not learn tables properly. When confronted with a situation where they
can't dive the computer (failure, loss, travel etc) these divers are at
a serious handicap.

[Omicron]

Excellent points, some of them. I said in the other thread as well, that a lot of these things seem to be "computers rot your brain, they're bad!!!". Eh...someday's...so what??? So what if the recreational diver that is never going below 80-100 feet doesn't have his tables memorized? What harm will it really do, as long as he's obeying NDL's??

One of the things I've always found interesting - and I'm kinda playing devil's advocate here - is a lot of people espouse the use of their own custom cut tables.

Well...how do you cut those tables? VPlanner? GUE's Deco Planner?? You're using a computer...no different than me, it's just that my tables are changing every second I'm down on my computer. I'm getting computer cut tables that are not as demanding on me - if I don't spend EXACTLY 5 minutes at EXACTLY 97 feet, my computer makes up for it for me, whereas w/ custom cut tables I'm SCREWED! Unless of course I'm carrying half a dozen sets of backup tables...but then again...my dive computer kinda does that for me on the fly.

[FreediveWI]

IF your at 80' on nitrox, which you could afford if you didn't buy a $900 computer, you wouldn't have too much to worry about in terms of deco- assuming your diving a single tank and look at you tables before you go.

As far as computer failiure goes when generating tables, like on Dplan, we each make our own and check them with our buddies before we jump in. We know ahead of time how it should work out- which is really important for deco! I have seen people get into real trouble with air integrated computers when they go into deco. The computer tells them they have enough air to do the dive, but they have no idea if they have enough to deco out after the dive! I have evenseen problems with limited deco, under 15 minutes, because the dive was probably done on a single tank to begin with and they doen't have the reserves to do it safely.

If your diving your computer to the knife's edge( 97' for 4 minutes) what will you do when it fails? Do you have a back-up computer, even more money, or do you use back-up tables? Do you have a back-up plan at all? If your close to 100' and close to deco I hope that you have some back-ups in place. IF you really like Uwatec I would highly recommend their bottom timer. IT is an awesomely simple, and less expensive, piece of gear.

Somone else mentioned that Halcyon wasn't cheap, but neither is OMS, or that over priced thing from Deep Outdoors. IF your looking at a BC even Zeagle's cost a lot of money these days. After I burned through a couple of Zeagles, they just seem to fall apart when you dive a lot, I finally went to backplate and wing for my single tank diving. This stuff is a whole lot more durable and you won't end up replacing it in a couple of years- depending upon how much you dive. Another bonus, for warm water divng, is that the plate and wing pack smaller than a Zeagle travel BC.



Someone also mentioned diving the Vienna. My deco times were much longer using a computer on that wreck than diving tables, mostly becasue of gas changes and deep stops. A wreck like the Vienna is starting to cross the line into tec diving where you should be on tables and using deco gas if oyu want ot get a good dive on her.

Jon

[Omicron]

Okay, I'm understanding your points here but enough on the price I paid for the computer. I bought it and am still not having any trouble getting fills on anything that I need. Can we consider that a dead point now???

As far as backups go while diving on the edge of deco using my computer...if i'm not entering deco, i technically don't NEED to have a huge worry. I can begin my ascent with appropriate safety stops and finish my dive with peace of mind.

If my computer dies during deco, I know the time of deco that I'm doing and I use my backup timer (or monitor a friends timer) to finish my obligation.

I was one of those talking about dives on the Vienna earlier, so I just cut a quick table using V-Planner...honestly, they don't look a lot different than what our dives were!!

And Jon - I'm NOT trying to be argumentative - I'm honestly enjoying this discussion

DIVE PLAN
Surface interval = 10 day 0 hr 0 min.
Altitude = 0ft
Conservatism = Nominal

Dec to 125ft   (2) on Air, 50ft/min descent.
Level 125ft 15:30 (18) on Air, 0.98 ppO2, 125ft END
Asc to 50ft   (20) on Air, -30ft/min ascent.
Stop at 50ft 0:30 (21) on Air, 0.52 ppO2, 50ft END
Stop at 40ft 1:00 (22) on Air, 0.46 ppO2, 40ft END
Stop at 30ft 3:00 (25) on Air, 0.40 ppO2, 30ft END
Stop at 20ft 4:00 (29) on Air, 0.33 ppO2, 20ft END
Stop at 10ft 7:00 (36) on Air, 0.27 ppO2, 10ft END
Asc to sfc.   (36) on Air, -30ft/min ascent.

Off gassing starts at 84 ft

[FreediveWI]

I'm NOT trying to be argumentative

No problem. This is always a good thing to discuss.

You already bought the computer and are happy with it, fine. You are doing mostly no-deco diving, also ok.

I am a little bit worried about going into "limited" deco without a backup. You should at least carry a set of tables. What happens if your computer goes out when your not looking at it and you know your in deco? those things rack up deco really quickly on the bottom and you need to be sure that you have the right numbers.

In the late 80's and early 90's we planned out our dives on Canadian Tables, and carried them as back ups, but used our computers on the bottom- Us divers Monitor's. THe dive times were always within in a minute of the tables no matter how much we swam up and down. More than once I had a computer fail on me, I had back up computers but quickly decided that back up tables were easier to carry. With all of the money I spent on computers and back up computers over the year I could have just bought a stage bottle setup and carried the correct deco gas to get me out of the water in a LOT less time.

WHen we dove the Vienna we dove to the bottom, around 140', for 30 minutes and, according to the Canadian tables which closely mimicked my computer, I would have had 48 minutes of deco to do. I just planned out the same dive on D-plan using air as a back gas and a deco gas and I only had 40 minutes of deco- same exact dive. If I paln the same dive properly, trimix and two stages, I only have 18 minutes of deco.

My deco times, using a computer with a computer back-up were regularly 45 minutes to an hour. Once you switch to the right gases adn stages they hardly ever go over 25 minutes.

If I have an opinion on something it's usally because I have done it other ways and foud a better one. I think that it would be good to share this with others so they can learn , and save moeny, for my mistakes. If people really insisit onmaking them over again themselves that's fine, but I didn't just read this stuff on the internet and decided it was best- I actually did the dives.


My point boils down to this. If you buy the right gear to begin with you will replace less of it in the long run, saving you money; not buy as much overpriced junk, which will save you money; and you will have more cash left to acutally go diving- the most important part. Even if you decided a computer is for you I think that money spent on a $900 computer could be better spent on a $400 computer and you could use the extra $500 to pay for the difference in nitrox fills over the cost of air fills. Nitrox offers huge, real, benefits in diving over some wirst worn computer. If you figure out a dive like the Dredge # 6 on the correct nitrox mix you can do over a 3 hour dive with no deco- who needs a computer for that!

Jon

[Deep Blue]

The biggest problem that I have with dive computers is that they tend to allow people to put their brains on autopilot. I seriously doubt that you could find anyone diving a computer that understands what their air consumption is, or could even hazard a guess about how long that tank on their back will last at their planned depth. (Planned depth? I just let my computer tell me that!!!) I have had numerous people tell me that they just dive until their computer tells them it is time to come up. That is it for their dive planning!!!!

While I don't have a huge issue with recreational divers using computers, as long as they do some predive planning, I do have a big problem with technical divers using wrist mounted computerst to plan their dives. When planning a technical dive, there are so many planning issues that need to be addressed, from gas requirements to gas choices, to conservatism levels to lost gas ramifications, that these items need to be addressed up front.

As far as I am concerned, there is no such thing as a little deco. That is like being a little pregnant. If you are going to stay withing the no deco limits, do so and feel free to use your computer. If you are going to be doing a deco dive, plan it right and set your computer to bottom timer mode.

Hate to sound hard core here, but I know that there is a substancial difference between deco and no deco diving. If you are going to involve yourself with an overhead condition, which you are doing when you are in deco, you need to be prepared and have a thourough understanding of what you are doing. I have seen too many people get themselved into trouble by only doing a "little deco" on their wristmounted coputer.

Now, if I can only find my way down off of this soap box!!!!

[Chris H]

I will be the first to admit that, in the past, I relied heavily on my computer to tell me how, and when, to do a dive. Like Jon mentioned, the Vienna was a bit beyond a recreational dive. I had a great time on it, but it also made me appreciate a lot of the things that have been said here, mostly by Jon and or Gert.

I have since taken a Nitrox course and made sure that I had a much better understanding of dive tables than I previously had. I need to do a bunch more reading to get a true understanding of what is going on. I, like Jason, have only done a handful of decompression dives, of which no stop was ever more that 15 minutes. There are many times when I would have loved to stay longer, but deco usually looms so the dive has to be terminated.

The other factor that seems to limit bottom time is the charter captains and their schedule. If you show up on a boat to do a really great dive, and there are others on the same boat who have a single 80, points are not made spending an hour + in the water. I know that now there are tech charters offered through Deep Blue (Thanks Gert) and possibly others too, but in the past the opportunity to even get into Deco on a lot of charters was very limited. It is partly because of these "tech" charters becoming more of the norm that I think it is time to consider where to go next with my diving. I don't care about deep at all. I have been this deep because I wanted to see 200 on my depth gauge? Forget it. However, if there is a great wreck in 150' of water, I have some interest. I also want it to be done as safe as possibe.

I need to learn some more things before the 100'+ dives, or anything that involes deco for that matter, become the norm for me. Gert, don't apoligize for being hard core, for most of us this is all new. Even if someone doesn't agree with statements made, it should at least make them stop and think. Your comments have done just that for me. Thanks.

[Deep Blue]

Chris,

You make some good points on the power of deco on deeper recreational depth wrecks. When I teach my decompression procedures, I do not frame it as a deep class. I personally have a strong belief that if you are going to dive deeper than 150 feet (I prefer if deeper than 130 feet) that you use helium in your breathing mix.

The most powerful aspect of the deco class that I teach is the ability to plan dives in the 130 foot range with respectable bottom times and still get out of the water in less than an hour. Even if you are on a recreational boat, as long as you are first in, limit your dive time to under an hour, you shouldn't get too many evil stares as you get out.

A great example is planning a dive on the Wisconsin for 130 feet, you can do a 30 minute bottom time, with EAN28 and carry 1 40 cubic foot bottle of EAN50 and your total deco is 12 minutes. You are out of the water in 45 minutes. This dive could be done on one big single, the Pressed Steel E150 comes to mind with room to spare the Totally cool even on the most recreational boat.

If you did that dive with air, and no deco gas, as would a person relying totally on their computer, you have 36 minutes of deco and at total dive time of 67 minutes for the same bottom dive!!!! For this dive you would need to carry 180 cubic feet of back gas to cover the dive and a reserve.

Gaining an understanding of gas planning and the effect of gas selection as well as dive planning suffers greatly when a diver relies too heavily on the computer on their wrist, and forgets about the one between their ears!!!!

[Omicron]

Yeah, I do know what you are talking about Gert. I've taken some of my favorite dives that I do on a regular basis and ran them through VPlanner using various gas combinations. It's amazing what carrying tank of 50% will do for your deco times!!!!

One of these days I may actually do the training so I can do those dives

[FreediveWI]

This article was just published on the Deeeper Blue website- not to be confused with the Deep Blue diveshop.

Diving Unplugged
Print | Email19 February 2004
By Paul Osmond


Email
Bio As my head broke the surface I immediately knew there was problem. Our Extended Range instructor and one of the students were lying on the tubes of the Zodiac, breathing O2 and appeared not to be moving. We doffed our gear and jumped into the boat, where we noticed that both divers where conscience and relatively comfortable. Amazingly both divers had survived an aborted deco from a dive approximately 180ft/60m for a total bottom time of about 20 minutes. The student had trouble venting gas from his wing, the instructor got involved and both were subsequently dragged to the surface. No attempt was made to recompress in water, instead both divers exited the water and opted to breathe O2 on the boat until the assistant instructor and I returned from our deco. The Coast Guard was notified and would meet us at the dock, which was only 10 minutes away.

Both divers were being closely monitored for the inevitable signs of Decompression Sickness, which thankfully never materialized. By the time we had reached the dock and unloaded, both divers were feeling better and on their feet. They decided to go to the hospital and get professionally checked over, but not to wait for the Coast Guard. They were notified that the situation had dramatically improved and that their services were no longer needed. By later that same evening both divers had been checked out and told it was safe to go home.

Approximately two years later I assisted another diver with a mild case of Type I DCS, who got hit after a second dive to 60ft/20m. In this case the diver had done one uneventful 60ft/20m dive for 40 minutes and did a second 60ft/20m dive about an hour or so later. On the second dive he had lost control of his buoyancy after about 30 minutes and bounced to the surface from about 30ft/10m. The DCS symptoms didn’t really start to manifest themselves until later that evening when the diver was at home. After an uncomfortable night and the discovery of a large rash on his abdomen the next day he decided to talk to me to see if this could be DCS. I was a co-worker and also an ERT (Emergency Response Team) member who had access to O2 and other first aide equipment. Hearing the story and recognizing basic Type I DCS symptoms, I immediately put the diver on O2 and transported him to a hyperbaric chamber where, happily, he made a quick recovery.

It was these two incidents that, for me, emphasized the fact that decompression is a very mysterious animal and can vary dramatically between individuals. I realized that the algorithms, tables and the other deco aides cannot possibly fully understand what is going on inside any one person, and how they must be made very generic and wildly conservative to account for the diving population as a whole. Granted, it was most likely the quick intervention of O2 that separated the first incident from the second, however, the physiological make up, fitness level and predisposition to DCS of the divers could not be overlooked. Ultimately I was less willing to trust blindly any computer, table or deco algorithm and wanted to understand better the deco process in relation to human physiology.





The way I dive now is radically different from my earlier years, my increased understanding of decompression coupled with better physical fitness; minimalist gear configuration, proper gas mixtures and team work have greatly enhanced my enjoyment and freedom in diving. One of the biggest changes, or leaps of faith, was the elimination of a wrist/console mounted dive computer, now instead I use a bottom timer, dive tables and complete dive planning.

Dive computers can be useful if you just want to do a series of multi-day air dives and staying well within accepted decompression limits. They allow for simple fun diving but do have disadvantages that can pose problems for an inexperienced diver. Computers reduce the amount of dive planning needed to do a dive, so a failure may leave an unprepared diver no choice but to “wing it”. Even when divers are wearing identical computers the schedules they output may be different because of slight variations in depth, time or number of dives done that day. In my opinion this is the most insidious disadvantage because an inexperienced diver may choose to follow their own computer, rather then staying close to their buddy, and slowly become separated in the water column. The buddy may even be close but a diver’s attention could be more focused on the computer causing a lack of awareness. In either case a diver may fail to notice that their buddy is in trouble.

When entering the realm of technical diving most diving computers offer no advantages at all to a diver. They do little to make a diver better or ready for more advanced dives, usually do not account for multiple gas mixes and often have annoying bells and whistles telling you that you are doing something crazy. Most importantly, like in recreational diving, increased dependence on a computer reduces the need for proper dive and contingency planning.

Diving unplugged forces a diver to rely on the “computer between the ears”, which is far more dependable then a black box on your wrist. It requires you and your buddy to plan your dive ahead of time; agreeing on decompression schedules, turn time, max depth, contingency plans, etc. These plans can be entered on a slate or wet notes taken with the diver and referenced when needed. It guarantees that you and your buddy are using the same plan throughout the dive, allows divers to stay close to each other and allows for quicker spotting of issues since both divers should be doing the same thing at the same time. Most importantly it forces you to understand the dives and your body at a level you would never achieve by depending solely on a computer.





The proponents of computers often argue that a computer gives you more freedom because any drastic unexpected changes in a dive plan can be calculated instantly and the deco profile altered on the fly. This is true, to a point; the big problem occurs when dives/deco need to be abbreviated or aborted because of low on gas, medical issues, dry suit floods, fatigue, toxing, weather, whatever. In these cases a computer will not understand that you need to reach the surface as soon as possible and will complain that you are flying through your deco schedule, possibly adding to the stress level of an already stressed diver. Once the problem has been dealt with a diver may have the option of going back and redoing some of the missed deco to reduce any chance of injury, however, many computers will go into a lockout mode or think it is another dive and pad the schedule more then necessary. In these situations a diver is back to using the “computer between the ears”.

As a diver gets used to diving within a certain depth/time and using the same deco schedule for that range, they will soon come to recognize familiar feelings within their body for each phase of the dive and post dive. Any variation from this norm may mean that a diver has done something wrong or, potentially, has done something more correct. In some cases it may mean on that particular day they could have been dealing with other issues like cold, dehydration or fatigue, etc. When a diver comes to understand their body in relation to a particular type of dive, they now have a “barometer” in which to gauge the dive and improve upon existing deco schedules and practices. However, this understanding only comes from the repetition of doing the same plan for the same (kind of) dive, not from the day to day randomness of following a dive computer.

The best use of a computer in diving is via your PC or Palm Pilot. Here you can run various decompression programs, cut tables for different gas mixtures and do virtual dives to check out the “what if’s”. You can alter things like gradient factors, conservativeness, deco algorithms, gas mixtures and a myriad of other options to help you fully understand how these factors interact (or at least within the program).Also, if you are reading this article I am sure you know, the Internet is a vast storehouse of diving knowledge with many sites displaying the planning and background for a large number of dives. Many sites have scuba forums where a diver can post questions, browse archives or get in touch with divers around the world. The internet is the biggest diving resource today and will enhance a diver’s knowledge and dependability far better then a black box on the wrist.

Sources:

Here are a few of the sites that have helped me over the years. I use substantially more then is listed, but these are the ones I go to on a regular basis.