Place of dive tables in modern diving

[agilis]

The number of actual human errors is ginormous. Some are worried that a PDC might fail, but to err is human. We are defined by the fact that we are going to screw up. We are our weakest link and our worst enemy. The irony is that so many refuse to trust the more trustworthy of the two. Hubris? Luddism? Technophobia? Bad at choosing? There are many reasons for this, but it's obvious to me that the PDC is far more reliable than my brain at depth.

A brain familiar with the tables on a basic level together with a computer seems to be an excellent combination. There is never an advantage in not knowing something.

 

[kelemvor]

A brain familiar with the tables on a basic level together with a computer seems to be an excellent combination. There is never an advantage in not knowing something.

Fair enough.. and that's how my NAUI OW course went. We learned both. We were required to plan an execute the dives based on the table data. We were all provided an AI computer to use on all the dives but we had to follow the table. I think I still followed the table for my first year of diving. Not that it mattered really. None of my dives in that year were NDL limited.

 

[The Chairman]

A brain familiar with the tables on a basic level together with a computer seems to be an excellent combination.

The rule of 120 is enough. It's easy to check any PDC against that criteria. It's easy to teach to students as well.

 

[J-Vo]

1. All the cases I know of occurred at altitude--not quite 5,000 feet. We were told not to adjust Ratio Deco in any way for altitude, because altitude does not matter for decompression. Since that contradicts what everyone else believes, I asked how they knew it was safe to use RD at altitude without adjustment. I was told two reasons: 1) Andrew dives at Lake Tahoe without adjusting, and he is fine. 2) No one has ever been bent at altitude using RD. I responded that all the people in our group who had gotten bent were using RD at altitude. I was told those did not count, because there was some other reason for their being bent. I asked what those reasons were. They didn't know--maybe PFOs, maybe something else. How did they know it was not Ratio Deco? Because no one gets bent diving at altitude using RD, so therefore it had to be something else.

.

Circular logic works because circular logic works.

 

[The Chairman]

Fair enough.. and that's how my NAUI OW course went. We learned both.

True story. I was having this "Teaching tables vs PDC" with a NAUI course director. He tells me that he has proof that PDCs are more dangerous and proceeds to call up a dive profile from a returned PDC on his computer. The lady that had bought it complained that all it did was beep at her the whole time. Well, it appears that she had blown off 17 minutes of deco and it locked her out on the subsequent dives. The PDC wasn't defective, but her training was. No, it wasn't covered in her class. No, there was no training done by the shop that sold her the PDC. After we sussed things over for a bit, it was obvious that he was exposed to legal prosecution should she have been bent misusing her new PDC. The man taught PDCs in every class after that (or so he told me) and no PDC was to leave the shop until the buyer had demonstrated their ability to set it and describe how/why alarms would go off.

 

[Wookie]

***MOD POST***

It didn't stay basic. The split thread is in the advanced forum. If you want to post in this thread, see the special rules.

Place of dive tables in modern diving (Split from the basic thread)

 

[Rich Keller]

In the spirit on not hijacking another thread I thought I should take start this discussion from a fresh page. The event that I am describing below is true though my memory of depth and bottom time numbers that I state below may be off since this happened in 2008 and I was a new diver.

I got certified to dive in the year 2004. Dive computers were not very common and my whole class was trained to dive using dive tables. Everyone in the class knew the set point of 60 by 60. For the first dive of the day, 60/60 would be the start of our No decompression limit calculations. We knew that if the dive depth had not exceeded 60 feet then our bottom time could easily be 60 minutes. It was really that simple! Then, for 70 feet we would have a bottom time of 50 and for 80 it would be 40. The above depth and time limits were ingrained into our minds and we would remember them like we would remember our mothers name. This meant that for the first dive of the day, no one needed to even look at tables. We knew the available dive time for each depth from pure memory. It was for the second dive that dive tables were pulled out and and adjusted no-decompression limit were read, noted down on a slate and then we jumped in.

This was diving for me in the early 2000s. Then I stayed out of water for many years until I returned back to diving in 2008. Between the years of 2004 to 2008 the computer revolution happened and dive computers went from being a luxury item to a mandatory item on many dive operations. Upon my return to diving, I signed up to dive a wreck which was resting at 130 feet while the top was 50'ish. The dive operation insisted that since this wreck has many decks and different people are interested in exploring different depths, everyone should have a dive computer. I had not used a dive computer up until then and did not feel the need for it but the dive operator said that computers are mandatory on this dive. I ended up renting one.

This was the second charter of the day and the dive computer that I was given had already been used by a diver who was on the first charter and had done two dives on the same wreck with that computer. The dive operator gave me the computer without resetting it and I ended up wearing a computer that believed that the dive I was about to do would be my THIRD DIVE of the day. I was told by the dive operator that the computer will activate itself at 5 feet depth so just go and dive mate! When we splashed and I reached the top of the wreck at 60, I knew from the table ingrained in my memory that I should have 60 minutes at least. The computer was giving much less than that. I knew right away that this device is dead wrong but I did not know why. There were two things about the computer that were correct though. Depth and bottom time. As a table diver, that is all I needed to complete the dive. During the dive, I exceeded the projected no decompression limit which would have applied to the fellow who wore the computer before me. I ignored the warnings and proceeded to dive my no decompression limit from memory. When I surfaced, all alarms were going off and I knew that they were wrong. The dive boat went into panic mode because a diver just surfaced with warnings beeping on the computer!

The dive master looked at the computer and said that I had gone deep into decompression and I needed to be checked for symptoms. He started to run a decompression diagnosis on me while the deck hand was preparing to put me on 100% oxygen. I tried to explain to them that I can’t be in decompression because my depth was less than 70 and my bottom time was less than 50. Any diver knowing tables would know that the numbers I am stating mean that I was safe but behold ... the computer revolution had started and the age of electronic stupidity had begun. In this age it was not only possible to become a certified diver without knowing dive tables but was also possible to become a divemaster and lead dives without knowing depth and table limits. When computer said you were surfaced while in deco, all dive theory and basic common sense was abandoned and 100 percent oxygen was to be given.

Fortunately, other people began to surface from the dive. One of these was a dinosaur from the pre-historic era. He had been diving since the earth was very young and there were no dive computers. He saw all the chaos and asked me two questions. "How deep were you?" and "what was your bottom time?" I was relieved to see that someone spoke the same language instead of "What is your computer saying?". He told the DM that there must be something wrong with the computer because 70 feet and less than 50 minutes is really not an emergency. He kept asking me “Are you sure about your max depth and bottom time?” I told him yes. Then they all began to fiddle with the computer and it turned out that I was right and the computer was wrong! Since data from the previous dive had not been deleted, the computer calculated it to be my "third dive." The guy before me had taken the computer really really deep so the computer was seriously freaking out on this “third dive.” The confusion did not last very long and life went back to normal but had the dinosaur from the prehistoric age not emerged from the ocean then I this “lets follow the computer crowd" would have put me on pure oxygen or I would be getting evacuated by a helicopter to the nearest decompression chamber.

Today there are agencies that train you to dive on computers from day one and they are proud of it. It is seen as a sign of embracing tomorrow and being progressive. The questions is not whether computers are good or bad but whether we are using the computer to advance our thought or whether we are using it to think for us? Furthermore what is wrong in using a multiple tool approach to planning dives? Diving courses of today are loaded with so much nonsense (boat dive specialty, shore dive specialty, put your mask on specialty, take your own fins off specialty) what is wrong with creating divers who are as proficient on tables as they are on computers?

Thoughts?

I come from the age of dinosaurs as well and still don't use a computer. Back then we didn't even have waterproof charts. I would write the no decompression limits on the arm of my wetsuit with indelible ink. There was also a simple rule of thumb that we used at the time, if you stayed above 60' diving a single 72 you would run short of air before you were down long enough to get bent. The computers take you closer to the edge of getting bent then the tables would allow. It will allow for slightly longer dives but at a greater risk of being bent. I don't see that as an acceptable risk for a few extra minutes. Even if people are shown how to use the tables it is not stressed much and is soon forgotten by the student. In the end you are responsible for your own safety, I would not abdicate that responsibility to a computer or the batteries that run it.

 

[boulderjohn]

I don't see that as an acceptable risk for a few extra minutes.

That depends upon the dive. If you are diving with some of the operators in Cozumel using HP 120 steel tanks, you will go to a maximum depth of 80-100 feet and end up with an 80 minute dive (using, say, EANx 32). That can be nearly an extra hour. I recently mentioned a dive I did in Bali last year with a maximum depth of 103 feet using EANx 32 in an AL 80. Using tables, my bottom time would have been 25 minutes. Using a computer, I went well over an hour.

 

[Rich Keller]

That depends upon the dive.

That depends on the computer too. I know who came up with the Navy tables. I have no idea who set the limits on any given computer.

 

[lermontov]

That depends on the computer too. I know who came up with the Navy tables. I have no idea who set the limits on any given computer.

i suppose you still own a typewriter too