Why do some agencies recommend using a bottom timer instead of a computer

[boulderjohn]

. Again IMO its the dir thing. a computer is subject to failing and its primary purpose is to compute deco. To these folks it is un-necessary as they use ratio deco or some dirivative of it.

The idea that a computer can fail is at the heart of it. The unspoken second half to the argument is that the human mind is in contrast incapable of error.

I discussed this recently in a blog post here. That blog post is being discussed currently here.

 

[boulderjohn]

Well point 1 and 13 are still valid...the rest are somewhere between questionable and just not true with modern computers.

I agree--but let's look at #1 and #13, the most valid of these reasons, in more detail.

1) Dive computers tend to induce significant levels of diver dependance, eliminating the awareness so common and essential to all diving but particularly obvious when diving tables

What I find best about the use of computers (combination of desktop planning and the dive computer itself) is how it can influence planning and decision making. In planning a dive, we can go through a variety of scenarios quickly as we determine the best dive plan for what we intend to do. I am really at a loss to understand the difference, at least in technical diving. I agree it is true in recreational diving.​

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.

Failure or loss of a computer would be on the same order of probability as the failure or loss of a bottom timer. This one argues that if you didn't have access to your computer, then you could use your bottom timer if you knew the tables. Well, if you had two computers, you could use the second computer. In technical diving, you need a backup, and you should of course know how to use your backup, whatever it is. Since you don't start a dive without a backup, then the loss or failure of a computer is exactly the equivalent of the loss of a bottom timer.
​

As a whole, the 13 points all ignore the one I find most important--the relative reliability of the two modes of conducting your dive plan. If your computer fails during a dive, you should see that and respond appropriately, either by ascending to the surface on a recreational dive or switching to your backup on a technical dive. If you make a mental mistake during your dive, you will not know it, and you will base remaining decisions on the dive you thought you did rather than the dive you actually did. As my blog post mentioned above points out, the odds of the human brain making such an error are far, far more likely than is a computer failure.

 

[NAM001]

boulderjohn has made excellent points. There is a major difference in the abilities of technical, seasoned, and newby divers. Find a new diver, or say one with 100 dives, and ask them what the NDL is for for say 40, 60.100 ft,,,, from memory. they probably can not tell you. Ask them their consumptiion rate for a specified depth, and they don't know. what do you do if you exceed NDL by say 5 min. They don't know. The only thing worse than a not so good plan is having no plan at all. the computer negates these issues as long as the computer is working. Other questions to ask. if you have been diving for 15 min at a constant depth how much air will you use? If you use 500 psi at 60 ft how much time has passed? Ask what is a tank factor is? If you have time and psi used, can you determine what depth you are at? All these are mental tools to use to at least SWAG time and depth. With out them you can not even begin to work a deco problem, even if you knew how. Again the computer localizes all that data in one contraption. For those that do not use a computer adn think a bottom timer is the same,, think of this, depth time psi is on 3 different contraptions and a failure of one can be delt with much easior than the failure of all 3 inputs. Computers are a major convienience till it fails. Now throw one variable in the mix like varying depths and you are screwed for the most part if you dont know if you round your depths up or down, same goes for time and how about sac or rmv. The theorys needed to do this are no longer present in OW or AOW training. Discussion regarding dive tables on this board have been beaten to depth and called unneeded to be taught. If you dont have a computer and were taught , like so many, to clear your mask, exhale on ascent, recover your reg and then sign for receiving your OW card, you are screwed in an sensor equipment casualiy. The answer is always if you have an equipment problem end the dive. Or use your buddy's indicators for his depth and times and do an immediate staged ascent, which will probably work 99.9% of the time, because 99.9% you have no problems. Until you get separated. Bottom line is these skills do not happen in a three day course on a vacation. Many of them cant be used by those that dive rarely or rent gear and have bad buoyancy etc. My opinion has always been , use your head if you want but have the computer to verify your thoughts,,, or use the computer and then use your head to verify the rational of the data from your computer. Baing NARCed is still a factor in divingand effects rational.

There is a lake i go to and i can do a shoreline dive around the parimeter. I can tell by the SPG how close to the exit point i am. I can tell by the compass when i start going in circles what part of the lake i am at. I can look at teh spg and get a rough idea about far time wise i am into the dive and I can check that and be reasonable close. Thats in 30 ft of water and there is noproblem of blowing and going up if needed at that depth. but it is a process of honing skills through being aware of your surroundings and indications. I know that if I am at 100 ft and the spg says i have 700 psi on a lp tank ive been down about 15-20 nminutes. If problems occur i ignore the gas I am using (IE 32%) and use the standard numbers for air and head up. If water is less than ideal (low vis) I notice when the light starts to fade and note that depth . When i come up i have an idea when I reach 25-30 ft if a stop is necessary. When it comes to ascents test your self by not using your computer to hold depth. use the light penetration and ear pressure senses as a depth gage. Use your spg and mental clock (one thousand one , ect) to guess 3 minutes stop. After a while (and a long one at that). you will become much less dependant on your computer. I by n o means am suggestin ignoring the computer but to skill yourself to come to the same conclusions as your computer. Computers seldom fail,,,,,,, but computer and mask straps do!!!!!

 

[dmaziuk]

what do you do if you exceed NDL by say 5 min. They don't know.

In all fairness, that is in the (PADI at least) book that they were supposed to study and pass the test on. It boils down to a very simple rule, and if they don't know/remember it, that's on them. You can't overcome stupid, computers or no computers.

 

[NAM001]

In all fairness, that is in the (PADI at least) book that they were supposed to study and pass the test on. It boils down to a very simple rule, and if they don't know/remember it, that's on them. You can't overcome stupid, computers or no computers.

I agree because once they leave the conditions of No DECO diving they have left the arena of rec diving. You are absolutely correct in that ....You can't overcome stupid, computers or no computers. As a side note Padi says no diving below 60 ft without AOW (or further training) (*also a highly debatable aspect as to the meaning) so you cant surpass NDL on a single dive without runingout of air, or probably a 2 or maybe 3 tank dive day with reasonable SI's.

 

[NAM001]

In all fairness, that is in the (PADI at least) book that they were supposed to study and pass the test on. It boils down to a very simple rule, and if they don't know/remember it, that's on them. You can't overcome stupid, computers or no computers.

I agree with you. Padi I believe says no training below something like 40' for OW and what 100 ft for AOW. At 40 feet a tank should last you about what 50 minutes for a new diver and the NDL should be (120 rule) minimum 80 min. 60 ft 60 min. With those factors there is no need to push the dedicated training time involving NDL issues for OW divers. Although they do cover it just enough to legally cover them selves. IMO Minimum standards do not foster mastering of skills. That is where the instructor becomes the most valuable asset to the training.

Back to the meat of the OP.... those agencies do not stop at passing upon demonstration of recovering regulator the min of 2 times. They pass at mastering of them at a variety of conditions. Again each course functions as a prep for the next course which requires strict adherance to required skills as prereq to starting the next phase of training. I hate to say it but they teach to make quality divers. They do not teach to make 200$.

As uase of computers go. They are training with the ultimate goal of tech diving. You dont use computers on tech dives so they dont start their intro diving courses with computers involved. It is easier to teach the final method once than it is to reteach progressive changes in methods. First learned first remembered first mastered. And mastering to tech quality is the goal from day one. Other agencies goal is to master to the satisfaction of the course time frame for conditions that do not exceed the level of the current training needs.

I dont know the detail of the more tech agencies but I would suspect they do not teach CESA as that is a shallow water skill and is not advantagous for deep water prespective training. I would expect them to teach prevention of a problem with solutions usable at any depth and not depth specific recovery attempts like CESA. One should never have to consider CESA with a buddy in hand. And they do push buddy system very hard from the comments I have seen.

 

[boulderjohn]

I agree because once they leave the conditions of No DECO diving they have left the arena of rec diving. You are absolutely correct in that ....You can't overcome stupid, computers or no computers. As a side note Padi says no diving below 60 ft without AOW (or further training) (*also a highly debatable aspect as to the meaning) so you cant surpass NDL on a single dive without runingout of air, or probably a 2 or maybe 3 tank dive day with reasonable SI's.

PADI recommends that you do not surpass your OW training limits without additional "training and experience." Conversations with PADI indicate that the phrase means training and/or experience"--both are not required. Neitehr can actually be required in the real world, because neither PADI nor any other agency can establish rules to giovern you in your diving.

 

[dmaziuk]

I agree because once they leave the conditions of No DECO diving they have left the arena of rec diving.

That's not what I said, nor what the book says. Yes, by OW rules that may constitute an "emergency", but the procedure for such "emergency" decompression without a computer has been taught to everyone with a PADI OW cert and no further training.

 

[NAM001]

That's not what I said, nor what the book says. Yes, by OW rules that may constitute an "emergency", but the procedure for such "emergency" decompression without a computer has been taught to everyone with a PADI OW cert and no further training.

My point was that if you stay in the relm of less than 60 ft (PADI'S RECOMMENDED LIMIT FOR OW DIVING) you can not get into a deco problem unless you push repeditive dives to exceed the NDL. Most DECO issues do not raise their head till you get past 60 ft and approach 100 ft. Thats the AOW arena.

Back to the OP I would doubt that those referenced agencies would teach safety stops. I SUSPECT they teach it as mandatory stops so that their proceedures are constant no matter what depth you are ascending form. Again I am no authority of their courses. They have a more stringent set of goals and purpose than say padi or ssi etc.

 

[boulderjohn]

I agree with you. Padi I believe says no training below something like 40' for OW and what 100 ft for AOW. At 40 feet a tank should last you about what 50 minutes for a new diver and the NDL should be (120 rule) minimum 80 min. 60 ft 60 min. With those factors there is no need to push the dedicated training time involving NDL issues for OW divers. Although they do cover it just enough to legally cover them selves. IMO Minimum standards do not foster mastering of skills. That is where the instructor becomes the most valuable asset to the training.

Back to the meat of the OP.... those agencies do not stop at passing upon demonstration of recovering regulator the min of 2 times. They pass at mastering of them at a variety of conditions. Again each course functions as a prep for the next course which requires strict adherance to required skills as prereq to starting the next phase of training. I hate to say it but they teach to make quality divers. They do not teach to make 200$.

As uase of computers go. They are training with the ultimate goal of tech diving. You dont use computers on tech dives so they dont start their intro diving courses with computers involved. It is easier to teach the final method once than it is to reteach progressive changes in methods. First learned first remembered first mastered. And mastering to tech quality is the goal from day one. Other agencies goal is to master to the satisfaction of the course time frame for conditions that do not exceed the level of the current training needs.

I dont know the detail of the more tech agencies but I would suspect they do not teach CESA as that is a shallow water skill and is not advantagous for deep water prespective training. I would expect them to teach prevention of a problem with solutions usable at any depth and not depth specific recovery attempts like CESA. One should never have to consider CESA with a buddy in hand. And they do push buddy system very hard from the comments I have seen.

I am very confused about what agencies you are talking about in much of this thread, so the following points may or may not apply.

• I wouid guess that the majority of tech divers today use computers. If I have seen a tech diver in the last two years without a computer, I missed it.
• CESA is absolutely not appropriate for tech diving--you have to solve your problems under water because of a decompression obligation.
• I believe the agencies described in this thread do not teach CESA in their beginning classes, either.
• I believe every agency teaches all levels of diving within the NDLs in their OW classes. I don't believe anyone teaches to just be above 40 feet and you'll be OK.
• Things like the rule of 120 only apply to certain dive tables and do not work with others.