Ambitious newb: Researching PDCs and relevant background info

[TSandM]

The battery issue I was referring to is peculiar to transmitters, because they have no battery indicators. Dive computers generally do, so you can know if your battery is getting low before it cuts out on you.

As far as the other issues -- there are two ways to dive. One is reactive, which is what is taught to open water divers. You get in the water and swim around until you hit some kind of limit, whether it's decompression, gas, or thermal tolerance, and then you end the dive.

The other approach is Proactive, where the dive is planned. You know before you get in what profile you intend to do (roughly), how long you can stay, how much gas you are going to use, and how you are going to execute your ascent. This approach is taught to technical divers, and it changes the way you approach diving. With all that planning already done, your gauges become almost a backup, because you already know what you are going to do. If something changes during the dive, you can recalculate, but in general, you don't change your dives in a direction that makes them less conservative than what you planned.

For example, I might be on a boat where the guide says we're going to go down on a reef that runs along a ridge at about 80 feet. I know from experience that on 32%, I have about 20 minutes of no-deco time at that depth. I calculate my gas supply and consumption, and the reserve I need for me and a buddy to get to the surface from that depth, and conclude I have enough gas for the dive. At that point, my dive computer is just a cross-check, and my SPG is primarily to alert me to anything (like an unrecognized current) that might make my gas consumption higher than normal. I'll check the gauge every five minutes for the first couple of checks, and then, if it's tracking what I predicted, I might drop off to every ten minutes. See why I don't think I need the information on my wrist?

 

[stuartv]

The battery issue I was referring to is peculiar to transmitters, because they have no battery indicators. Dive computers generally do, so you can know if your battery is getting low before it cuts out on you.

The Hollis TX-1 shows the transmitter battery status on the PDC display. It will display an alert when the TX battery gets low and an alarm when it gets very low.

Plus, the PDC battery is rated for 300 dive hours and the TX battery is rated for 1500 dive hours. So, like I said before, if you change the TX battery every time you change the PDC battery, you should never have a problem with the TX battery dying unexpectedly.

http://www.hollis.com/tx1-trimix-computer/

Also, at least one other wireless AI I looked at has a ring around the TX that lights up that uses a different color to indicate battery condition, I think.

---------- Post added September 7th, 2014 at 02:06 AM ----------

A Petrel and a Predator controller, yep. And an analog depth gauge, an analog dive watch, and pre-cut tables. Multiple backups are good when you're several hours away from being able to surface.



This isn't as complicated as you're making it out to be: you plan and cut tables for the deepest, longest dive you might do and then you dive within the plan. If all goes well, the Petrel has you out of the water before the plan would because nobody's doing a perfectly square profile; if all goes to you don't have to recalculate anything, you just dive no deeper or longer than originally planned and wind up doing a little extra deco.

Gotcha. Thank you.

---------- Post added September 7th, 2014 at 02:18 AM ----------

Bollucks! Is the best thing I can come up with! Most simply put - the last thing you want to do, is to be relying on a computer to tell you anything like what you just wrote above. By the time you get to the point in your diving where this would be an "option" - and it would not surprise me if you get there sooner than later - you will look back on this and smile! I promise!

Bollocks is right! [emoji2] I didn't say anything about RELYING on a PDC for what I was talking about. What I said was, if you're switching gases and using a PDC, then my understanding is that you switch bottles and you also perform an operation on the PDC to tell it what gas you switched to.

Now, if you accidentally switch your computer to the wrong gas, there's nothing that will alert you to that fact, right? And if you are following your plan and switched to the correct bottle, it might not even affect your dive. But, if you use that same computer for a repetitive dive, it's going to calculate things based on incorrect data about your current N2 and O2 debts, right?

But, if your computer had AI, it could catch your error and prevent all that. How is that a bad thing? How is it bollocks? Does noone ever make a mistake when changing gases on their Petrel and fail to catch it right away? Maybe even fail to catch it at all?

---------- Post added September 7th, 2014 at 02:45 AM ----------

Also, at least one other wireless AI I looked at has a ring around the TX that lights up that uses a different color to indicate battery condition, I think.

I was wrong on this. It's the Suunto TX that has the lighted ring. It lights up to show that it's on but does not have any indicator of a low battery condition.

However, the Suunto PDC (I checked the D9 manual) works like the Hollis. The PDC itself will display an indication that the TX battery is low.

 

[Dr. Lecter]

But, if your computer had AI, it could catch your error and prevent all that. How is that a bad thing? How is it bollocks? Does noone ever make a mistake when changing gases on their Petrel and fail to catch it right away? Maybe even fail to catch it at all?

If you ever get to a point where you're actually performing gas-switching during a dive, you'll understand why this is simply not how things are done. The computer is great for crunching depth/time data vs. your desired algorithm, but it is not a backup to your brain for all aspects of the dive. If you can't properly execute a gas switch, the solution is to learn how to do it...not backstop yourself with a bunch of transmitters and a more complicated computer.

Then again, maybe it is...have you considered diving a Poseidon Mk VII? I think it might suit you very well.

 

[PfcAJ]

There's really only one way to prevent switching to the wrong gas. Mark your tanks appropriately, analyze your tanks, look at the sticker and make sure its correct before you put the reg in your mouth, and have someone double check it. Skip one of those steps and you're asking for a bad time.

Add ons and gimmicks only serve to complicate the issue. KISS.

 

[lv2dive]

See my comments within the text...

...
Bollocks is right! [emoji2] I didn't say anything about RELYING on a PDC for what I was talking about.
Well if you are counting on the computer as a backup to "alert you" that you don't have gas turned on or that the gas is the wrong mix (which would be beyond the capabilities of the computer) I call that that "relying on" the computer. po-tay-to, po-tah-to

What I said was, if you're switching gases and using a PDC, then my understanding is that you switch bottles and you also perform an operation on the PDC to tell it what gas you switched to.
Yes this is true

Now, if you accidentally switch your computer to the wrong gas, there's nothing that will alert you to that fact, right?
Incorrect. You should have planned your dive and suddenly the deco time is inconsistent with the plan. So as a thinking diver you would figure out why.

And if you are following your plan and switched to the correct bottle, it might not even affect your dive.
Well if you switched to the correct bottle but didn't change your computer correctly, it WOULD affect your dive - if you switched to the wrong gas on your computer, you would have either done more or less deco than required. Period.

But, if you use that same computer for a repetitive dive, it's going to calculate things based on incorrect data about your current N2 and O2 debts, right?
As discussed above.

But, if your computer had AI, it could catch your error and prevent all that. How is that a bad thing? How is it bollocks? Does noone ever make a mistake when changing gases on their Petrel and fail to catch it right away? Maybe even fail to catch it at all?
Computer being AI would do nothing to catch it. All of the bottles would be charged and ready to go, you would still have to tell teh AI which one you were breathing.

 

[Lorenzoid]

. . .

And then, obviously, there's a whole bunch of posts recommending PDCs - even from the serious Tech divers.

These attitudes seem contradictory to me. I assume that means I just don't understand the subject well enough yet. . . .

By now you've probably figured out that SB is largely a discussion board, and you're not going to get many black and white answers to ANY question. What you'll get here are looks at different schools of thought and approaches. After you've dived a lot, you will get a feel for what the different approaches and philosophies are, and find yourself persuaded by some and not by others. You dive, you read, you dive, you discuss, you dive, and so on--and your diving and mindset evolve. This is why I think SB can be a double-edged sword for new divers. It can be a great help and yet can also distract new divers from things they should really be focusing on. I suspect the whole idea of selecting and using a dive computer is captivating to a software guy like you. Input to be gathered, analyses to be made, and then a shiny new electronic thing to play with! I get it--I am in a 12-step program for former techies.

. . .
And again, this not about Tech diving or what you experienced divers do. It's about what you recommend to new divers. . . .

There are a lot of tech divers on SB, and some of what they have learned from tech diving can be applicable to improving recreational diving, and they want to share that with us. But it's hard for someone without any diving experience to speak of to make really informed decisions as to what to adopt and what to ignore.

Not too many new divers end up saying "I hate my computer." I don't mean to say you are WAY overthinking this decision (just overthinking it maybe a little bit) or that you should just choose any old computer. What I guess I'm trying to say is that after you've been diving a while the choice of that first computer becomes a distant memory for many of us. There is so much more to diving than that computer. My recommendation would be to do your homework--as you clearly have done--and then follow your instincts and buy what appeals to you. It's possible that one's whole approach to diving changes over time, and with those changes may come new gear decisions. Who knows. I think you will be satisfied for a long time with whatever computer you choose.

 

[stuartv]

See my comments within the text...
Computer being AI would do nothing to catch it. All of the bottles would be charged and ready to go, you would still have to tell teh AI which one you were breathing.

Right... And what I said was, IF you switch your PDC to a different gas than what you physically switched to, the AI PDC would detect that the gas you selected is not dropping in pressure, so it would alert you that you switched the PDC to a different gas than what you are physically using. Sure, a thinking diver would notice the deco times on their PDC are all off from what is expected. But, how quickly would that happen and they catch their mistake? Or, might a thinking diver simply change their PDC to the new (incorrect, in this scenario) gas, and then use their dive plan and bottom timer to deco, and never notice that the PDC is wrong? Or might a thinking diver be varying from their dive plan (in a more conservative way) and notice the difference in deco, but chalk it up to their variance from the dive plan?


Anyway... this conversation has gone way past what I need to know to help me select a PDC to buy, so I'll let it rest now.

Thank you to all of you that have shared your experience with me. I know that my questions may make it seem differently, but I do put a LOT of value on learning from other people's experience, so this has definitely helped me. All my questions are because I like to understand, as best my knowledge and experience level will let me, the thought behind the choices and recommendations of more knowledgeable and experienced people. Playing Devil's Advocate does not mean that I actually hold the position it may seem like I'm arguing for. It just means I'm trying to fully understand YOUR reasons for your position.

Thanks again!

---------- Post added September 8th, 2014 at 01:07 PM ----------

By now you've probably figured out that SB is largely a discussion board, and you're not going to get many black and white answers to ANY question. What you'll get here are looks at different schools of thought and approaches. After you've dived a lot, you will get a feel for what the different approaches and philosophies are, and find yourself persuaded by some and not by others. You dive, you read, you dive, you discuss, you dive, and so on--and your diving and mindset evolve. This is why I think SB can be a double-edged sword for new divers. It can be a great help and yet can also distract new divers from things they should really be focusing on. I suspect the whole idea of selecting and using a dive computer is captivating to a software guy like you. Input to be gathered, analyses to be made, and then a shiny new electronic thing to play with! I get it--I am in a 12-step program for former techies.

I see we've met.

I will end up with a shiny new toy to play with, regardless. My problem is that I am very much a KISS (Keep it Simple, Stupid) guy. I like simple and streamlined. The idea of 4 hoses coming off my 1st stage and having two different places to check my dive info is, well, the old school approach. And, obviously, it does work. But, the idea of having only 2 hoses (plus a wireless TX and using a hybrid Octo) coming off my 1st stage and only having 1 place to look for all my dive info seems (SEEMS, mind you, to my inexperienced mind) like a much simpler, more streamlined configuration. And that has a lot of appeal to me.

But, I expect I will just let the whole subject lie for now and wait until I finish my OW certification before I make any decisions. That way I can also get input from my OW class instructor, too. He already steered me away from some of the snorkeling gear I was going to buy (based on Internet reading, of course) into different gear - and yes, I actually listened to him and bought based on his suggestions instead of what the interwebs told me.

 

[rivers]

Right... And what I said was, IF you switch your PDC to a different gas than what you physically switched to, the AI PDC would detect that the gas you selected is not dropping in pressure, so it would alert you that you switched the PDC to a different gas than what you are physically using. Sure, a thinking diver would notice the deco times on their PDC are all off from what is expected. But, how quickly would that happen and they catch their mistake? Or, might a thinking diver simply change their PDC to the new (incorrect, in this scenario) gas, and then use their dive plan and bottom timer to deco, and never notice that the PDC is wrong? Or might a thinking diver be varying from their dive plan (in a more conservative way) and notice the difference in deco, but chalk it up to their variance from the dive plan?

The thing is, when you get to a point where you are diving with multiple gases, there is a checks and balances system in place to make sure you are switching to the right gas before you even pop the reg in your gob. If you switch to the wrong gas, it can kill you. Divers who are diving with multiple gases do not rely on a computer to tell them what they are breathing.
For example, at the moment, if I'm diving with a stage, it's only one stage. But, before I switch to it, I confirm that it is A) my stage and has the right gas in it, B) check to make sure the reg i have in my hand is attached to stage, and C) have my buddy or team confirm that it is in fact the right stage/reg and I am switching at the right depth for the gas in that cylinder. Reason being, if I ever add a second stage to the equation, i already have the checks and balances system in place to make sure i do not under any circumstances switch to the wrong gas at depth. Or in an every day scenario I am likely to encounter, I've picked the wrong stage up from the rope where everyone hangs their stages at my local quarry (I like to practice gas switches and sometimes, it's a bottom stage in case I'm trying to use up the gas in my twinset).
It is good that you're asking these questions, but you if you ever get to the point in your diving where these questions will become relevant, you'll understand the answers you've been given.

 

[stuartv]

The thing is, when you get to a point where you are diving with multiple gases, there is a checks and balances system in place to make sure you are switching to the right gas before you even pop the reg in your gob. If you switch to the wrong gas, it can kill you. Divers who are diving with multiple gases do not rely on a computer to tell them what they are breathing.
For example, at the moment, if I'm diving with a stage, it's only one stage. But, before I switch to it, I confirm that it is A) my stage and has the right gas in it, B) check to make sure the reg i have in my hand is attached to stage, and C) have my buddy or team confirm that it is in fact the right stage/reg and I am switching at the right depth for the gas in that cylinder. Reason being, if I ever add a second stage to the equation, i already have the checks and balances system in place to make sure i do not under any circumstances switch to the wrong gas at depth. Or in an every day scenario I am likely to encounter, I've picked the wrong stage up from the rope where everyone hangs their stages at my local quarry (I like to practice gas switches and sometimes, it's a bottom stage in case I'm trying to use up the gas in my twinset).
It is good that you're asking these questions, but you if you ever get to the point in your diving where these questions will become relevant, you'll understand the answers you've been given.

I think I understand perfectly well the answers I've been given. I have almost no diving experience, but I have a LOT of experience with activities that can get you killed and using processes with checks and balances to ensure that you don't make a mistake and die. I understand very well the concepts of planning and redundant processes to cover contingencies that shouldn't happen but do anyway.

What I also think is that the people responding to me don't understand me. They all respond (including yours) as if I'm suggesting something that would replace any of their existing checks or balances or knowledge or experience - which I am not. Several responses have even addressed the issue of physically switching to the wrong gas, which I have never brought up as a scenario.

All I have asked about is the possibility that you make a mistake during the process you are already using, with your existing equipment - i.e. that you select the wrong gas on your PDC. And all the responses so far indicate that, either, nobody EVER makes that mistake, or, that everyone always follows their processes and checks and balances so perfectly that if they ever did make that mistake, they would catch it immediately (or close enough that it makes no difference). Either way, all responses indicate that there is NO value in an additional check-and-balance being added to the process. None of the responses have said "well, yes, that extra check-and-balance would be nice, but it's not worth the extra money." None of them have said, "well, yes, that extra check-and-balance would be nice, but it's not worth the tradeoff in questionable reliability of a wireless SPG - even if it's backed up by a traditional one."

Nope, all the responses to this question have either been "there is no value in that extra check-and-balance" or they've been off-topic (talking about physically switching to the wrong gas).

 

[eelnoraa]

First, slow way down. Just get your OW cert, enjoy the rec diving. Forget about different mix and multi gas deco diving. By the time you get there, the cost of training, other equipment, even the gas, will make buying another computer seems like peanuts. And chances are you may not have intention to go there.

Have that said, I would recommend a first computer to be wrist mount, air and nitrox support, and gauge mode. Easy to read is a bug plus. AI capable if you need it. And don't need to go crazy on a top of the line model. With these consider, I think the best bang for the buch for is:
https://www.divegearexpress.com/computers/dg03.shtml

If you ever move to trimix deep deco dive. You can set this computer into gauge mode as a backup.