Computer or Not

[darkpup]

Hi Jason,

I asume you are asking about the 4 reasons?

60 ft: Any dive below 60ft would be rounded to 70 ft, which would give you a NDL of aroud, off the top of my head, 35 min or so. Well a diver who is good on air runs the chance of running out of BT before running out of air. Thus, a computer is a good, constant reminder.

More than 2 dives: Assuming we're not talking about 30ft dives over 12 hours... Using a computer multiple dives gives more bottom time for each dive, and removes some human error from SI calculations.

Nitrox dive: same as a deep dive, but now you have oxygen toxicity to consider as well. Again, a computer is a safe and easy way to accuratley track the N2, and O2 levels in your body.

Multi day: Similar to more than 2 dives as above.

Just my 2 cents,

Cheers,

Divebutt

Out of curiousity, what tables are you referencing in your calculations?

It sounds to me like the tables you're using are more complex than they need to be. The idea of human error suggests that the computer algorithm used to create the tables is so accurate that 5 to 10 minutes off on your SI might cause a problem. Since I know that isn't the case, I'm not sure how bad you'd have to mess up your SI to actually cause a problem.

The rule of thumb with regards to SI that I use is: 90 minute SI = clean, < 90 SI = double safety stop on 2nd, 3rd, 4th, or 5th dive. That's not complex or difficult to remember, nor does it require a computer. In most cases we're talking a 10 minute safety stop on repetitive dives vs. a 5 minute stop, and I'm pretty sure your computer follows a similar pattern.

As for multiple dives over multiple days while tracking CNS % and OTUs while on Nitrox, I just don't see that as being difficult either. Nick commented about how easy it was to calculate CNS% (i.e. BT / 2 / 200 = CNS%), and OTUs are just as simple (BT * 1.5 = OTUs). These calculations are based on an average ppO2 of 1.2.

Have you ever run the numbers to see how many dives you'd have to do per day to hit your limits? You're talking more than 400 minutes (~ 6 hours, 40 minutes) on 32% Nitrox at depths of 100' in a single day. For a recreational diver, is this even remotely possible when you take into consideration surface intervals and the gas in a single tank? At 5 dives a day, you might hit 50% of your daily CNS % if you really push things. Is that likely?

The only argument so far that I agree with is that computers make things convenient, especially for new divers that may not have the experience to effectively track this information. However, when you know how to do what your computer does for you, the convenience aspect, for me at least, disappears.

The point I'm trying to make is that computers aren't the only way, and IMO every person should make a well educated decision on whether to use a computer or not. Each method requires certain skills and understanding, and without the "Why's" behind some of the blanket statements made about computers, it's difficult for new divers to fully understand the impact using a computer may have on them.

I'm in no way saying that one way or the other is better. I'm not saying in anyway that computers will kill you because I obviously don't believe that's even remotely the case. I'm just saying there are ways to effectively plan and safely execute multiple dives over multiple days without the use of a computer, and a large part of my reason for this comes for the Tech training I've undertaken.

~ Jason

 

[Jetskiman]

There is another reason to have a computer. A certifying agency, such as SDI, requires them.

 

[nyprrthd]

And I forgot another thing......

I download my dive data to my laptop, and use the graph function. I'm definitely still working on my skills, and the graph shows me where I may have ascended too fast or done something else that needs work. One of the most important is that my graphs showed that I was yo-yo'ing during my safety stops. So...... I've been consciously working on improving. Helping me to become a safer diver.

 

[darkpup]

Lou,

In no way am I saying you're wrong. The more you learn about diving, the more you'll realize there's not a single way to do things. Even for the type of diving I'm involved in.

My purpose for asking the question is to get people to think about the "Why's" behind the statements, and to possibly show another approach to the problem.

Ok, let me see if I have this right. The reasons you give for computers being safer than tables are:

1. Real Time information (depth, deco, remaining BT, CNS %, rate of ascent, etc)
2. Flexibility vs. Rigidity
3. Makes diving Nitrox easier (i.e. computer keeps track of CNS % / OTUs rather than relying on tables)

The above helps you plan dives, conveniently track Nitrox related details, and gives you real time information that helps you safely execute your dive on the fly in the event something changes. Let me know if I'm on track, and here are two follow up questions for you.

Is it possible to get the same flexibility from tables as you do from a computer?

If No, then what tables are you using?

I'm hoping to continue the conversation, and see if we can define some details as we go. The topic of decompression models is quite large, and is not an exact science.

~ Jason

Darkpup - As you can see from my profile, I am a newbie of the first order. Please take that into account:

Why computers add safety:

I use my computer in conjunction with standard dive planning tools, and employ the dive planning function in my computer. While I'm on a dive, I get real-time dive data that lets me know how well I'm following my plan, and if I need to make any adjustments. I think that sticking rigidly to a plan, without having said real-time data is equally as dangerous as relying on the computer without engaging ones brain. If I question my computer, I have a dive watch/bottom timer and analog gauges to use as a double check. If my computer indicators start to get into the yelllow-towards-red area, I simply ascend to a more shallow depth and stay there until I'm back in the green. Much safer, in my opinion, than guessing.

Since I dive Nitrox, there are added steps in planning and execution that require cross-referencing different tables. Much easier to use the computer, and double check against the tables.

As it has been stated in many posts, dive conditions can change rapidly, and blow your plan out of the water (pun intended). My computer helps me to access my current situation, and aids me in making what could be life saving decisions.

But... these are my opinions, and I could be wrong.

 

[darkpup]

And I forgot another thing......

I download my dive data to my laptop, and use the graph function. I'm definitely still working on my skills, and the graph shows me where I may have ascended too fast or done something else that needs work. One of the most important is that my graphs showed that I was yo-yo'ing during my safety stops. So...... I've been consciously working on improving. Helping me to become a safer diver.

Ok, you got me there. The cool factor for graphs is high, but I still think you can come to the same conclusions without the use of a computer.

~ Jason

 

[Red Vette]

I have 2 Cobra's, Stinger, D9 ,Vytec and a VR3. I use my Cobra's for back up and I think its a great beginner computer. I can not imagine diving with out a computer! The ability to know my remaining No Deco time, remaining air time at the given depth I am, safety stop/deco timer plus the ability to plan my next dives quickly....it just goes on. I tell my students to give up Starbucks twice a week and you have paid for the computer in one year. I agree, it should be one of the first items you purchase!

 

[darkpup]

I have 2 Cobra's, Stinger, D9 ,Vytec and a VR3. I use my Cobra's for back up and I think its a great beginner computer. I can not imagine diving with out a computer! The ability to know my remaining No Deco time, remaining air time at the given depth I am, safety stop/deco timer plus the ability to plan my next dives quickly....it just goes on. I tell my students to give up Starbucks twice a week and you have paid for the computer in one year. I agree, it should be one of the first items you purchase!

If only that worked for my Scooter budget.

~ Jason

 

[nyprrthd]

Jason,

By no means am I saying that you can't do the same things with the tables that you can with a computer, as far as "doing the math" and planning/monitoring your dive. The algorythms are basically the same. As you can tell from my back-up systems, I don't put blind faith in any electronic gizmatron. As others have said, it's a tool, and not a substitute for your brain. Computers crash and freeze; and I've seen too many PDA's drop dead with no warning. If my dive computer drops dead during a dive, I can recoup the necessary info by looking at my bottom timer and gauges (my depth gauge has a max depth needle). I couldn't recoup the multi-level info, so I would have to proceed based on the table; and I would default to the air tables even if I was diving Nitrox. I keep a table in my BC pocket, just in case. If I didn't feel comfortable with that, I would simply call the dive and do an extra long safety stop for good measure. I could then calculate my pressure group back on the boat, using tables, and determine when/if I could do another dive. I've been told that as long as I had my max depth and bottom time, I would be OK reverting to the tables. Someone please chime in if I've been misinformed.

Call me lazy, but, when I'm 70 feet +/- underwater, the last thing I want to do is attempt to calculate my remaining NDL based on time spent at each depth. The computer keeps track of everything I need to know, and I can access the info with the push or two of a button. I try to swim with my hands folded in front of/under me, when I'm not taking pictures, and find it handy to glance down at my wrist every couple of minutes to see how I'm doing (I have an air integrated wrist model).

Another real-world situation that makes the computer an extra safety measure: Have you ever been on a dive, and spotted something that you just HAD to go check out? I have, and took off after a school of eagle rays towards the end of one dive. As Murphy's Law would have it, I was swimming against the current (love my Apollo fins!). After they proved that they can swim a lot faster against a current than I can, I looked at my computer. Lo and behold, I had not only sucked down my tank to 850 psi, but the bottom evidently sloped downward where I was chasing them. Mr. Computer told me that I only had 5 minutes of NDL time left. I floated on the current back to the group, while ascending a little as I went. The computer told me that I was coming back from "yellow to green." It was towards the end of the dive, so I didn't miss anything; and simply proceeded to my safety stop with the rest of the group. The temporary loss of my sanity is a discussion for another thread, but it shows how a computer can help, especially if you get excited, and lose track. Are dive computers the end-all and be-all for dive safety? Not in my opinion; but anything that can facilitate a more comfortable and safe dive is worth getting, if your budget allows. You can always rent (or borrow) a computer a few times, and decide for yourself.

BTW, as I swam towards the eagle rays, they got spooked and all 7 "took off." It was a sight to behold! When I turned back towards the group, I did notice the divemaster watching me like a hawk as I pulled this less-than-sane stunt.

 

[tstormdiver]

I do not yet have a computer. I would like to eventually get one, but being a new diver, I think it would be prudent to thoroughly learn how to use the diving tables, then graduate to a computer. The computers are a wonderful addition to any set of dive equipment, but I feel a diver should also have a good knowlege of the dive tables as a back up.

 

[nyprrthd]

Tammy,

To play devil's advocate for a minute, consider another way to look at your timeline. By using a computer, and then playing my dives back against the tables, I've gained a better understanding of the tables and how they work. The graph readout available with many dive computers (uploaded data to a PC/Mac) allows you to see exactly how much time you spent at each depth, and you can then do the math to estimate how the computer came to its conclusions. As I mentioned in another post, I also use the graphs to help me identify things that I need to work on. When I was a kid, I used to take things apart to see how they worked, so this is a logical extension, without disassembling my dive computer.

I think a computer is just as valid for a newbie as it is for an experienced diver, simply for the fact that it reduces the task loading of trying to calculate your status while perfecting all of the other skills. Not trying to be a PITA, but, as Jason said, there is no ONE way to look at this question. Many divers have gone diving for many years without ever using a computer. Could I dive without my computer? Absolutely! But why would I want to?