Hypothetical - 2 AI transmitters instead of backup SPG?

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Wow - lots of silly assumptions there... I know my Perdix AI and Teric inside and out. I also fully understand dive tables and how to use them.

I do 3-4 week long+ dive trips a year and don't ever want to have to cut a dive short or affect subsequent dives because I had a computer or transmitter failure (as unlikely as that actually is) - so I have full redundancy. Batteries are also cheap and easy to swap out, so I typically replace the batteries in my transmitters every other dive trip (and always carry spares). My Perdix AI has a battery level indicator as does the Teric - so easy to see when the Perdix needs replacement or the Teric recharged (Teric lasts several days but normally drop it on a QI pad every night on a trip anyhow). I'm not sure why you seem to have such an issue with this approach - it works perfectly for me!

To the OP - it's not a dumb idea and, if you have the means and deisire to do so, there is nothing wrong with a 2 transmitter (or even 2 computer) set up. Ignore the naysayers and equip yourself as you see fit in this area!

My issue is that just because it works for you at your level of compitance does not mean it is sound advice for others,

As haveing a spare comuter goes then I am somewhat like you however i leave my spare computer in the bag until i need it depending on the dive. Shallow dives you dont need one pter let alone 2.

Every time you change batteries you weaken the integrity of the area involving the battery. Whether you get a slight cross thread or get a spec of something on the oring etc. With a SPG you never have those issues. Generally if it is water tight on monday it will be 10 years form now also. I dont know much about the teric but i do have preditors and petrels. Shearwaters are made for the user to maintain unlike other brands. I am a die hard shearwater fan. That aside most can not handle one puter let alone 2. And many can not change from air to nitrox with out a book. Given that my comment was regarding computers in general and not specific the teric.

Most do not many know their puters inside and out and that is where first the problem starts and second they loose sight of what is needed. vs what complicates a problem. In most cases more is not better.

As to your comment to the OP,,,, If they can manage 2 comuters then fine. MOst people can not. Also as the rec world goes the puter is really nothing more than an electronic dive table, depth gage and watch. On a rec dive you dont need tables so a 1000 dollar backup is a pretty expensive depth gage and watch.
 
I dont think you have any concept of what constitutes failure points or behaviors at all. You premis of diffferent time of purchase making the argument moot is also moot. Same goes with computers if you and your wife send in your gear for annuals you quite often send the puters in also for fresh batteries to dive the year on.

I change the battery in my computer when it reads low. It's user replaceable and I carry spares and O-rings in my save-a-dive-kit. I don't send it out or replace the battery every year just because I'm having my gear done. It's a waste of money and bad for the environment. That's another advantage of having a backup computer- you don't have to be as concerned with changing the battery on your primary. As an aside- I don't send out my gear for service every year, perhaps the regulators only get serviced. I mail them without the hoses to a reg tech I met online for about $35 each.

I maintain gear for myself, my girlfriend, her son, and my two sibling dive buddies, and I've got a handful of spares- so between all of us including backups, that's over a dozen dive computers and NEVER has more than one computer indicated LOW BATT anywhere close to the same time.
 
1. you are getting overly personal rather than keeping the discussion reasoned and respectful.



2. That is not how failure probabilities work. If you have two 18 wheelers get transmissions rebuilt at the same time and then subsequently exhibit similar driving profiles the two transmissions will likely not both fail at the same time or near the same time, in fact the probability of that occurring is rather remote. There are far too many other variables at play in when a failure will occur. Manufacture quality of individual parts, quality of workmanship, random effects that cannot be predicted (bug in the grease) etc etc etc. Most mechanical failure is modeled as an inverted bell curve with a higher probability of initial failure with the probability rapidly declining over the lifespan of the device and than rapidly increasing later in its lifespan. I would really recommend reading a book or article on Reliability Centered Maintenance, it is a concept that the Air Force developed for aircraft maintenance and has subsequently been adopted by much of the automobile industry and other industries as well. It may be superseded in the future by the development of onboard sensors but not yet.


WOW I think you have missed the whole point of the conversation and are digging to justify/defend the practice for the sake of defending something. Not that I am defending them but the DIR folks would tear you viewpoint to shreads. When and If a failure occures it does not make a difference what statistical curve you are using because it failed ( the reason if not important) and you have to recover. The idea is to implement things with the least probability of failure. My point in this has been and is still if a SPG will do the job for 100$ than why use another device that costs much more and is the same catagory of item that has just failed? People can do what they want, they alone are responsible for their dives and no one else. My position is one of process and not about giving or denying permission.
 
Batteries are also cheap and easy to swap out, so I typically replace the batteries in my transmitters every other dive trip (and always carry spares). My Perdix AI has a battery level indicator as does the Teric - so easy to see when the Perdix needs replacement or the Teric recharged

That seems excessive. The lithium CR3 batteries in my transmitters have lasted over 5 years, and as with yours there's a low battery indicator and at least with my transmitter it's as easy as changing a TV remote battery, so why toss out perfectly good batteries (and O-rings), it's not good for the environment and a waste of money even if it's not all that much? There's also a slightly greater chance of a battery compartment flood after a battery change, why risk it?

I can say personally the i have had many xmitter failures and computer failures and I no longer use xmitter's becasue of those failures

Something's wrong. Either you're using poorly manufactured gear, you're not maintaining it well, having it serviced by incompetent techs, or you're just really unlucky.
 
That seems excessive. The lithium CR3 batteries in my transmitters have lasted over 5 years, and as with yours there's a low battery indicator and at least with my transmitter it's as easy as changing a TV remote battery, so why toss out perfectly good batteries, it's not good for the environment and a waste of money even if it's not all that much?
I have other uses for them so I don't just throw them out after I swap out from the transmitters. When I do eventually throw them out I also take them to a battery drop off location - they don't go in the trash!
 
I change the battery in my computer when it reads low. It's user replaceable and I carry spares and O-rings in my save-a-dive-kit. I don't send it out or replace the battery every year just because I'm having my gear done. It's a waste of money and bad for the environment. That's another advantage of having a backup computer- you don't have to be as concerned with changing the battery on your primary. As an aside- I don't send out my gear for service every year, perhaps the regulators only get serviced. I mail them without the hoses to a reg tech I met online for about $35 each.

I maintain gear for myself, my girlfriend, her son, and my two sibling dive buddies, and I've got a handful of spares- so between all of us including backups, that's over a dozen dive computers and NEVER has more than one computer indicated LOW BATT anywhere close to the same time.

Good for you . You may be able to do this but most are not. And if some bozo messes it up then you get what you get and he probably messes up all teh gear you sent to them.
 
You may be able to do this but most are not.

How do you know most dive computers do not have user replaceable batteries?. Have you researched dive computers and based on solid data you have arrived at the correct conclusion that most divers use dive computers that do not have user replaceable batteries?

And if some bozo messes it up then you get what you get and he probably messes up all teh gear you sent to them.

I have no clue what you mean about some bozo messing up all the gear he is sent. I send my regulators to a regulator technician that has done a fine job to date (I also purchase from him), and from speaking with him and diving the regulators after service, I trust that he knows what he's doing. Whenever you hand your life support gear off to someone to service you are putting your life in their hands, and there's always a possibility that they're going to get it wrong. No clue what relevance a technician's ability has to this discussion, especially given that you send your gear off for service every year and face the same risks that the rest of us do.
 
The 18-Wheeler analogy was spot on.

All analogies suck, but car analogies suck particularly hard. Some devices have a bathtub failure curve, some follow the bell curve, and for some others it's pretty much a line. Failure rates of 18-wheeler gearboxes are about as relevant to dive computers as the phase of the moon: to colour of my underwear.
 
How do you know most dive computers do not have user replaceable batteries?. Have you researched dive computers and based on solid data you have arrived at the correct conclusion that most divers use dive computers that do not have user replaceable batteries?



I have no clue what you mean about some bozo messing up all the gear he is sent. I send my regulators to a regulator technician that has done a fine job to date (I also purchase from him), and from speaking with him and diving the regulators after service, I trust that he knows what he's doing. Whenever you hand your life support gear off to someone to service you are putting your life in their hands, and there's always a possibility that they're going to get it wrong. No clue what relevance a technician's ability has to this discussion, especially given that you send your gear off for service every year and face the same risks that the rest of us do.
You just answered your own question.
 

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