When computers fail

[padiscubapro]

Originally posted by sharpenu
True, IF the computer fails, you have no SPG. The point I am making is that the dive is over anyway. Let's be honest. The chances of a sudden failure are close to the odds of your first stage failing. Or your mask breaking. While you may have a redundant air supply, how many of us have a spare mask at 100 feet? What if the boat sinks? I guess I am trying to say that with the reliability of today's computers, the chances of computer failure are so small as to bring them to an acceptable level. The statement that you are smarter and less likely to err than a computer (made by some here) is the type of attitude that keeps me employed. Like it or not, we trust our lives to computers every day. Does your car have ABS? Do you fly to your destination?

You say how many have a spare mask??? Mast straps do break, and there is always the posibility of a carless diver kicking you in the face.
Anyone who is deco diving should be carring one, its no different than carrying a backup light. If you can't read your guages you cant do your deco stops.. Masks don't take up much space.. If I'm cold water diving its in a pouch on my drysuit leg.. otherwise its in a pouch nicely stowed away.

 

[Lost Yooper]

Even the most extreme of the cavers use computerized bottom timers such as the Uwetec/OMS or the Suunto Vyper (in gauge mode). The difference is that they don't rely on them. Like them, I have a simple (and cheap) Timex watch and a simple backup depth gauge (clipped off in my pocket). I keep my primary dive plan on my slate and a set of backup tables in my pocket (my buddy the same way).
Albeit, I'm describing a technical/deco type of dive here, the same type of logic can be applied to recreational dives. If you don't know enough about decompression procedures and what-not for your recreational dives, and are relying solely on a computer, then I think you may be begging for trouble.

The real problem with computers is their inadequate alogorithms coupled with clueless/improperly trained divers. A computer doesn't know how fat a person is, if they're properly hydrated, and other such relevant things. Sometimes, you might find that a recreational computer will get you out faster than a good set of tables, but have you offgassed properly? You have to think about what is more important (especially on repetitive diving days) -- quanity v. quality.

Take care.

Mike

 

[Hobbs]

Originally posted by BILLB
I know of many NE wreck divers who are DIR rigged and dive computers. In fact they dive with two computers. Now this is going to take a lot more money but then again, you can't take it with you!
-------------------------

Just would like to point out that a DIR rig is "usually" a two tank system with an isolation valve. However they dont proclaim the two gauge system with two manometers. or am I incorrect with this ?. please correct me if I am in error.
I have had some discussions with ppl who to "some" extent follow DIR standards and regulations, and NONE of them can say they have two HP hoses with manometers or computers on.
one on each . This makes atleast me wounder why that is.
since the isolation valve increases the chanses of something going wrong when filling or emptying the tanks.
example
when filling they might close the valve since it was open from the beggining and as a result only fill one tank = half the air supply.
when filling they might close the valve after = you think its open and you only have access to half the air system.

both of those scenarios should be detected way before in the water, but should have would have could have just isnt cutting it.
and still they are known to happen

 

[Lost Yooper]

Computers and DIR do not exactly fit into the same sentence very well -- much less air intergration anything and backup 'puters and pressure gauges.

As for the manifold, one has to be smarter than the manifold and keep an eye on everyone who's around your tanks. If I catch another person touching my valves, I'm going to bite their darned fingers off! Part of the predive check is to ensure your isolator is not closed. I had a captain of a recreational charter turn mine off right before I jumped into the water. Not particulary imusing, really. This is an important issue, but you can't blame the manifold.

Mike

BTW. That captain had quite a swim back to the dock .

 

[Hobbs]

Originally posted by Lost Yooper
Computers and DIR do not exactly fit into the same sentence very well -- much less air intergration anything and backup 'puters and pressure gauges.

As for the manifold, one has to be smarter than the manifold and keep an eye on everyone who's around your tanks. If I catch another person touching my valves, I'm going to bite their darned fingers off! Part of the predive check is to ensure your isolator is not closed. I had a captain of a recreational charter turn mine off right before I jumped into the water. Not particulary imusing, really. This is an important issue, but you can't blame the manifold.

Mike

BTW. That captain had quite a swim back to the dock .

its not the manifold system I am attacking wich you might have thought, its the fact that DIR users who normally is very well educated dont see the danger in only using one manometer
what if you have to for some reason close the connection valve, due to the system design it then means that you have lost half your air supply AND in worst case the manometer.

speaking of manifolds and such.
would it not be good to have a possibility to have the tanks and regulators work as both 2 single systems aswell as a unit system ? I cans see some advantages with this.

dive safe

 

[Lost Yooper]

I don't agree. They weigh the pro's and cons of most everything and determine the acceptable risk involved of each. Isolating the left post is not a "normal" emergency to say the least. Keep in mind, that a strict buddy system is fundemental in DIR, and if properly executed will get you out danger. That's how I see it.

On your second point, I believe you are talking about independant doubles. This stuff just introduces a whole series of problems that are totally unnecessary. Like most things, by trying to fix a problem that shouldn't exist in the first place, people often introduce even worse problems.

Mike

 

[Hobbs]

Originally posted by Lost Yooper
I don't agree. They weigh the pro's and cons of most everything and determine the acceptable risk involved of each. Isolating the left post is not a "normal" emergency to say the least. Keep in mind, that a strict buddy system is fundemental in DIR, and if properly executed will get you out danger. That's how I see it.

On your second point, I believe you are talking about independant doubles. This stuff just introduces a whole series of problems that are totally unnecessary. Like most things, by trying to fix a problem that shouldn't exist in the first place, people often introduce even worse problems.

Mike

no i was thinking of a valve system that will make the dubble tank pack on my back work as EITHER indipendant or a redundant pair, now why would one want to do that I can hear you ask, well couse in case of an emergency you can actually save almost ALL air and use it.
I have never seen this type of valve systems since it would require atleast 5 valves to operate on the tanks.

and to the first point: what does your buddy know of your airsupply after a emergency ? and how does he know how much air you have leaft ESPECIALLY when he hasnt had the same malfunction.
lets be honest he doesnt know how much air you have left ! wouldnt it be better IF lets say YOU knew ?? and all that is required for that is a simple manometer!

so please tell me what are the advantages of NOT having two manometers and how do you /they (DIR) figure. Couse I cant figure it out. and please dont tell me the entanglement factor is to high or the danger of the manometer malfunction. give me a good reason so I can understand

Mike I am not trying to be a wise ass or so, just trying to figure out things for myself. hope you understand.

take care and safe diving

 

[Lost Yooper]

Ok, let's see here.

"no i was thinking of a valve system that will make the dubble tank pack on my back work as EITHER indipendant or a redundant pair, now why would one want to do that I can hear you ask, well couse in case of an emergency you can actually save almost ALL air and use it.
I have never seen this type of valve systems since it would require atleast 5 valves to operate on the tanks."

The type of system you describe is trying to solve a problem that isn't of significant risk (if I understand it right). The most common failure (at least that I've seen) is a right post free flow. With a manifold, you simply isolate it and you still have access to both tanks. The same thing can be said about the left post, but as you mention, you wouldn't know how much air is left.
Believe it or not, not knowing how much air you have left in your back tanks is not a really big deal assuming you have done everything right to begin with (rule of thirds and having a competant buddy). Assuming you had to isolate your left valve, you would terminate the dive -- no biggie. The only way you're not going to have full access to both tanks is if a neck O-ring or burst disk popped underwater. Then you would would have to isolate that tank (practically unheard of).

"and to the first point: what does your buddy know of your airsupply after a emergency ? and how does he know how much air you have leaft ESPECIALLY when he hasnt had the same malfunction.
lets be honest he doesnt know how much air you have left ! wouldnt it be better IF lets say YOU knew ?? and all that is required for that is a simple manometer!"

Not knowing isn't really a big deal, if you've done everything else right. If you're doing technical dives and are breathing your backgas down to 500psi, then maybe you would want to know. However, this is the wrong way to go about it anyway. There is no reason to introduce anything else to solve a problem that is very unlikely to occur, much less be critical if it did.

"so please tell me what are the advantages of NOT having two manometers and how do you /they (DIR) figure. Couse I cant figure it out. and please dont tell me the entanglement factor is to high or the danger of the manometer malfunction. give me a good reason so I can understand"

The advantage is having a simplified configuration that is efficient and provides sufficient redundancy for most realistic problems that could occur. By introducing other "stuff" to solve problems that not only shouldn't occur (but wouldn't matter if they did), you're more than likley adding problems that are more likely to occur. Get what I'm saying? If you don't need it, don't take it.

"Mike I am not trying to be a wise ass or so, just trying to figure out things for myself. hope you understand."

No sweat. Ask away, and I'll do my best to describe how I see things. Hopefully others get in here and fill in my gaps.

Mike

 

[budgy]

Before computer I used navy tables, now I dive with a computer, recently I have been using the buhlmann tables as a guide for pre-dive planning.
I agree with you when your cylinder contents, depth and time is in one electric gadget and fails, all you can do is cancel the dive. Hopefully your diving with the same buddy dived so it would be safe to do the same deco.

 

[Se7en]

Before I start, a disclaimer: I'm not trying to argue against DIR. I believe it is the system which has had the most examination of any that people dive, and therefore represents the current high water mark of gear configuration. That doesn't mean however, that it is necessarily perfect...

Originally posted by Lost Yooper

The most common failure (at least that I've seen) is a right post free flow.

The only way you're not going to have full access to both tanks is if a neck O-ring or burst disk popped underwater. Then you would would have to isolate that tank (practically unheard of).


The advantage is having a simplified configuration that is efficient and provides sufficient redundancy for most realistic problems that could occur. By introducing other "stuff" to solve problems that not only shouldn't occur (but wouldn't matter if they did), you're more than likley adding problems that are more likely to occur. Get what I'm saying? If you don't need it, don't take it.
Mike

Lost Yooper Mike

Doesn't this introduce a contradiction?

You (as an exponent of DIR) say that isolating a tank is practically unheard of - therefore two SPGs are NOT required for redundancy.

Yet DIR requires an isolation manifold - which sole purpose is to enable the isolation of a tank.

An isolator manifold also adds SIGNIFICANT complexity in terms of knowing which gas supply you are both breathing, and measuring the pressure of.

Surely on these grounds, the extra complexity of managing an isolation manifold, and the lack of requirements for one on the basis that tank O rings of burst valves practically never go, should indicate that the isolater is 'other stuff', that you don't need and shouldn't take?

Conversely, if you need the ability to isolate your tanks, why don't you need the ability to measure pressure in those tanks once isolated? After all, at this point you now have all the issues of managing independant doubles - with the added problem of not knowing how much gas you have in 1/2 of you system...


After all, even a free flowing first stage doesn't dump air that fast, and you have your buddy for backup...

Mike