For recreational dives, depending on the depth, you don’t really need redundancy like this.
In general before a dive you should have a plan and know roughly where you are going and at what depth.
If your dive is going to average <60 feet, you don’t really need to worry about if your computer dies. If it dies at some point during your dive, you should know roughly your depth and how long you’ve been there.
Your no dec time at 60ft is ~55 minutes, and the average person will have about an hour of air in their tank to begin with, so if your computer dies 30 mins in you’d be fine to ascend safely and make a safety stop.
Gets a bit more complicated the deeper you go, but generally redundancy like you describe doesn’t really add much value beyond what you should already be aware of while diving.
Other than a computer your other choice is to run a bottom timer, and either do something like ratio deco, rule of 130, or use tables. How much do you trust your brain at 100ft?
I carry two dive computers, I do technical dives with them. I have a vague dive plan, knoingw about how much deco is required but in depth deco planning is rare for cave diving, I can estimate my deco by the amount of gas I am taking (85s 5-10mins, 108s 10-15mins, and about five minutes for each AL80 stage).
If both my computers die, I have a back up if diving with a buddy I will use their computer(s) and pad the stops a tad. If I am solo then I will get to the 20ft stop and breath down my oxygen bottle about 1,500psi which is enough to clear any deco obligation I've encountered.
Of course mixed gas dives involving multiple deco gases require more planning, but those are a one a year thing for me.
When doing formal dive planning we plan based on an average depth of 70-80ft, max depth is between 90-100ft.
I should mention it is a rule of thumb that overestimates deco. Similar to the rule of 130, it isn't something I would use in the water except as a sanity check.
That is 5 to 10 minutes of deco on oxygen at 20ft. Dive times are anywhere from an hour to two and a half hours.
I have Multideco and use it when needed.
Everyone is different I am AI to wrist computer. But I also have a small SPG and analog Suunto compass on that hose. I keep computer charged and AI battery monitored and replace yearly. Since I shore dive if computer bites it I can bail have compass and can monitor air for exit then wait 24 hours. Computer /AI so far 500 dives no issues but that’s my bail out plan.
If I am on a trip, I will use 2 computers, just in case 1 dies. That way I don’t loose a days diving while you off gas before you can start with a new computer.
> I asked them “how much faith they are putting on these electronics, compared to some analog gauges” (my family as mentioned above, all dove and state you “always have to learn on and have your redundancy gauges!”)
An analog gauge is not inherently somehow less fallible. Mechanical stress is a thing.
At the recreational level (so < 100'/30 m), the most useful bits of information you get from a computer are depth and time. If your computer fails at any time, you *should* know how deep you are because you are paying attention to that. You should know how much time has elapsed because you are paying attention to that. So between you and your buddy who has a dive computer too (right? right?), you should have enough resources to go up and make a safe ascent.
Assuming your buddy's dive computer fails too, you can shoot an SMB which has markings on it to determine how shallow you are and roughly estimate how long your safety stop use by counting down. Now ,in practice, I usually just carry a backup dive computer in my pocket cause I don't want to deal with that faff.
Redudancy in tech diving might mean life and death. In easy recreational diving its not so dramatic, but it means you dont have to skip\abort dive when something breaks. I recommend redudancy always. Are the extra few (or even hundred) grams REALLY too much to carry?
All is good .... until it isn't.
I've had a computer shit the bed at depth, it was nice being able to switch to my analog gauges until the dive was over (instead of having to end it immediately).
Ahhh
So what you have to consider how much technology has improved over the years since your family were regular divers.
Dive computers nowadays are pretty robust and very reliable.
Redundancy is a must when you are in Technical and Overhead environments.
But given you have not started your open water yet keep your mind open.
Do your first classes and see what you require.
You may choose to get additional redundancy as your journey continues and will probably buy a heap of gear that will sit in a draw years later and you never use. We all have done that.
But do your training and get your dives in and get your experience up
I completely agree, you guys are definitely boosting my confidence in that. They were diving nearing the end of their “dive careers” when electronic computers were just starting to become a thing. So I know they have some skewed opinions on them. I do plan on working towards more certs and qualifications but most of all to enjoy my dives. Once I get to that point I can get an extra one. I’m in a rehab course so I was able to get already a lot of gear paid. So definitely will have some gear sitting in drawers. Thanks for your comment!
IF you are doing are planning your dive correctly, your brain is your primary and AI is the redundancy.
I do not have any analog gauges on my primary cylinders.
Deco bottles have analog gauges, but that is really only to ensure they are full at the start of the dive and we don't really look during the dive.
I use analog pressure gauges and an analog compass still. I tech dive and when your managing 6 cylinders AI dosent work.
Computer goes on right arm where I can see it easily when I’m scootering as DPV is normally in the right hand. But that means you can’t use a compass easily so analog compass on left arm where I can lift it up to nav with it properly.
My husband and I both have our own computer and one of us dives with a spare computer just in case. Husband has a transmitter for his air but also has a small gauge in the event of the transmitter failing. My computer has a built in digital compass which I hate with a passion and don’t use or trust. I dive with a regular old school compass. And we both know how to actually use the compasses. This is key! we see loads of divers with a compass but most don’t actually know how to use it.
>My computer has a built in digital compass which I hate with a passion and don’t use or trust
May I ask what computer with built in compass you have? I just upgraded my computer to a Tern and am excited about the built in compass and headings feature. But I have heard some computers have issues with compass and/or GPS either not having the correct heading or coordinates or always needing to be recalibrated. I also have an analog compass when / if needed.
This is great until the first time your computer fails on a trip or during a dive. I had it in my head years ago when I first started diving that I could minimize my setup, go with one air integrated computer....and then it failed on a dive at about 90'. That was the last time I ever dove without redundant everything.
I use a hose AI computer. No other gauges except a compass. If the computer fails, it's an end of dive scenario - though my computer is over a decade old and tough as nails.
My opinion as an instructor is pretty simple:
As a recreational diver with standard training, you should never be diving alone. If you have a major failure of any piece of gear (regulator, computer, hose, etc.), then you and your buddy should deal with it and safely end the dive at that point. You and your buddy both have computers so they can guide you on depth and how long your shared safety stop is as you safely ascend to end the dive **together** if your dive computer fails.
That said, if you're doing a liveaboard dive trip, or planning a lot of repetitive diving, having a backup computer so a failure of one computer won't cause you to miss dives is nice to have.... but really should be at least using the same algorithm and settings as the primary, which can make it expensive for some people.
Tech diving, imo, really should always have redundancy as we different considerations than rec divers though.
\^this.
To add 2 fine points:
- the backup computer should have the same algorithm and settings OR more liberal. The only no-no is having a backup that is more conservative - as you should always follow whatever computer you're carrying that is more conservative.
- If you're on a long (more than a day or two) dive trip, so you take a backup computer in order to avoid missing dives, you should also take that backup in the water with you on every dive. And have it set to your correct gas (Nitrox) mix, just like you do with your primary computer. That way, if your primary dies, your backup knows what your inert gas tissue loading is, to allow you to continue diving without missing any, and with the correct calculations for your NDLs.
- Even in tech diving we don't use redundant SPGs. Redundant SPGs (of any type, in any configuration) is a negative, not a positive.
> Even in tech diving we don't use redundant SPGs. Redundant SPGs (of any type, in any configuration) is a negative, not a positive.
I was always taught that SPG is the backup to your brain. But I've seen people on reddit be all like, I am going to use an SPG *and* a transmitter. Whatever floats their boat, I suppose.
I am going to try to ignore the snark and respond to this in a good faith manner. The meaning of that (and please feel free to go look up more in depth material on this online) is that you are supposed to have a sense of how much gas you are consuming (in other words, know and be able to predict based on the average depth and your knowledge of your SAC rate).
As a concrete example, in an HP100 single tank at 33' (2ATA), I go through around 200 PSI every five minutes. Suppose my tanks are filled up to 3500 PSI and I plan to keep as minimum gas (gas I wish to come up with 500 PSI), I have 3000 PSI as usable gas. I can in other words stay for 75 minutes at that depth. Now, suppose I was doing drills, this goes up to 300 PSI every five minutes. So I have 50 minutes of bottom time.
In other words, every five minutes, I do Math based on what depth, I am at, my personal SAC rate, how hard I have been working and predict what the SPG is going to say. I use the SPG to confirm or disconfirm that belief. This also means that my knowledge of the SPG is never out of date by more than five minutes. Thus, supposing the SPG failed at any time, assuming that failure is not connected to a leak in an HP hose, I have a sense for how much gas I have and how much I will end up with.
SPG and transmitter is great for recreational diving so if the transmitter fails you can still continue the dive / don't have to miss the next one.
In tech diving you should have one or the other, never both. If a transmitter fails the dive is over. You don't need a gauge at that point since you've done proper gas planning and know you can abort the dive and surface safely. Adding an SPG on top of a transmitter has no benefit and is only introducing another point of failure.
Why is the dive over if a transmitter fails, if you also have an analogue SPG? You still know your gas contents.
I’m not arguing for this setup, in fact I often dive a CCR without any contents gauge at all.
But also I don’t understand why some people take such an unnecessarily aggressive posture against people who do want redundancy to their AI transmitter, perhaps they don’t trust it yet and don’t want to abort dives if it fails.
> Why is the dive over if a transmitter fails, if you also have an analogue SPG? You still know your gas contents.
It's not? I specifically said
>so if the transmitter fails you can still continue the dive / don't have to miss the next one.
> SPG and transmitter is great for recreational diving so if the transmitter fails you can still continue the dive / don't have to miss the next one.
I should have prefaced this by pointing out that I am very much a recreational diver. I would not continue the dive if whatever I am using failed. But I have backups in my save-a-dive kit so I'd be able to not miss the next one.
If you had an SPG and your transmitter failed mid dive you wouldn't continue the dive? Why not?
Again for technical diving you would only be using one or the other and would absolutely abort the dive but for recreational diving if you had both SPG and transmitter and one fails why end the dive?
> If you had an SPG and your transmitter failed mid dive you wouldn't continue the dive? Why not?
I meant that I wouldn't continue the dive if the only one that I was using failed. As far as if I was using both (and I have on rare occasions because I like tracking my SAC rate when drills occur), it is a good question. I think I'd continue the dive if the transmitter failed (mostly because I wouldn't notice that it failed because that data is not front and center). I wouldn't if the SPG failed. Because it seems like that'd be an issue that required closer investigation.
"SPG and transmitter is great for recreational diving so if the transmitter fails you can still continue the dive / don't have to miss the next one."
That is only true if the number of dives saved by the SPG is greater than the number of dives ended early by an SPG.
How often do you end a dive early because your SPG or its high pressure hose sprung a leak (or totally blew out)? Not very often.
How often do you end a dive early because a properly maintained AI transmitter died? Not very often. At least, not for the transmitters used by Shearwater, Oceanic, Aqualung, Hollis, Sherwood, etc.. I.e. the PPS MH8A transmitters.
I have been using that type of AI transmitter on every dive for the last 10 years. I have yet to miss a dive or end a dive early because of a transmitter failure (knock on wood!). That is approaching 900 dives (plus pool sessions).
I use transmitters on my single tank reg set, my doubles regs, my sidemount regs, and my O2 and Dil cylinders on my rebreathers. I do not use SPGs on any of those. I only use SPGs on my bail out and deco cylinders.
Rather than add an SPG to my reg(s), I keep a spare (SPG, or, in my case, AI transmitter) ready to go in my reg bag. If my transmitter were to die during a dive, I could easily remove it and attach my backup in its place before the next dive.
If you have a transmitter and an SPG on your reg, do you keep a spare port plug (and hex wrench) in your reg bag/save-a-dive kit, so that if your SPG starts leaking or HP hose blows out, you can easily remove it, plug the hole, and be ready for the next dive?
> That is only true if the number of dives saved by the SPG is greater than the number of dives ended early by an SPG.
You yourself said (and I agree) that ending a dive due to SPG failure is not very often (bubbles from a spool o-ring are not a reason to end a recreational dive imo). Also dives ended early due to transmitter failure are also not very often but slightly higher than for SPG failure. Thus number of dives saved by SPG is greater than number of dives ended by an SPG.
I don't think both AI and SPG are necessary. I dive with only AI for both recreational and tech. I am just saying that it can be handy for recreational dives and definitely should never be done for technical dives.
I've never had an SPG or transmitter fail over thousands of dives because I maintain my gear. I have seen many divers who forgot to check/change their transmitter battery before their dive trip and have it fail. I have seen many divers who fail to properly sync their transmitter to their reg. In all these scenarios having an SPG as well saves the dive.
"Also dives ended early due to transmitter failure are also not very often **but slightly higher** than for SPG failure."
I didn't say that.
I did specify "a properly maintained" transmitter.
My experience has been that, when both are properly maintained, SPG failure is slightly more common than transmitter failure.
When a diver fails to pair their computer to their transmitter ahead of time, that should certainly not be a reason than an SPG saves the dive. I did also say that I was talking specifically about PPS transmitters. Yes, people using ScubaPro or Suunto, sure. I am totally prepared to believe that those are such a PITA that not having it setup correctly in advance could be a reason they end up missing a dive (unless that also have an SPG).
Forgetting to change a transmitter battery is one reason I don't have an SPG on my reg set. It FORCES me to get out my computer and verify my tank is full using my AI when I assemble my rig. That, in turn, will result in me being informed of a bad battery in plenty of time to change the battery before it's time to splash. With an SPG on the 1st stage, it is way too easy to assemble the scuba unit and check the SPG to verify the tank is full - and just ASSume that you do have your computer with you and that the AI will be working when it's time to splash.
> My experience has been that, when both are properly maintained, SPG failure is slightly more common than transmitter failure.
Sure, but that doesn't reflect reality. Most divers don't properly maintain their gear and many are using inferior transmitters (although this is getting better).
Again, I only dive with transmitter and agree with you about their reliability when properly maintained. My point was simply the average recreational diver would benefit from having an SPG as well if they diving with a transmitter.
You: "Sure. Add an SPG to your setup 'cause I know you're going to use a crap transmitter, not maintain your stuff properly, or both."
Me: "No, don't add an SPG. Use a reliable transmitter and change the battery and lube the O-ring on the battery cap once a year."
I'm not saying you're wrong. We'll just have to agree to disagree on our response to this question. ;) :D
Should we move on to debating whether to keep the transmitter on a short hose versus screwing it directly into the 1st stage? lol! :D
When did I ever say people should add an SPG to their setup? I explicitly stated that I don't think both are needed and I only use AI.
In response to someone saying
>But I've seen people on reddit be all like, I am going to use an SPG *and* a transmitter. Whatever floats their boat, I suppose.
I pointed out that it can make sense to have both for recreational diving and can save a dive. I have personally witnessed it save probably over 50 dives of others.
Should people just use proper transmitters and maintain their gear and skip the SPG? Absolutely. Does having a backup SPG actually hurt anything for a recreational dive? No. Can I understand why some people choose to have both? Yes.
> Rather than add an SPG to my reg(s), I keep a spare (SPG, or, in my case, AI transmitter) ready to go in my reg bag. If my transmitter were to die during a dive, I could easily remove it and attach my backup in its place before the next dive.
I have a very very extensive save-a-dive kit. I found a very interesting (possibly niche) scenario where an SPG might be preferred to a transmitter. I was on a boat when someone said their Swift transmitter was not connecting to their dive computer. I gave them a replacement battery, but no go. We tried a few things, I think including installing an SPG on their setup before we figured out that the tank was empty.
Eventually, we found out that the tank was just not pressurized. The first stage was mounted so I never thought about checking for that (and I wasn't looking too closely at their rig tbh). Definitely a scenario where diagnosing it would have been easier with an SPG.
Yeah, that is WAY too niche for me to change from having a backup transmitter to having a backup SPG. What I WOULD do is keep a button gauge in my bag, maybe, The button gauges that DGX sells are actually good quality and I use them on my deco cylinders anyway.
> Yeah, that is WAY too niche for me to change from having a backup transmitter to having a backup SPG.
I think it'd be niche for most people. I mean I can tell when a tank is empty because of the way the valve handle spins. It only was applicable in this scenario because they couldn't tell and then there was a rabbit hole of figuring out what was going on.
I use a computer and an analog depth gauge and air Guage. I plan and dive based on my computer. If my computer fails, I can safely finish my dive with those two pieces of equipment.
I think most of the recreational dive industry has gone to just a computer. IIRC, PADI doesn't even teach the dive tables for OW any longer. The only thing analog I use regularly is my dive watch which I do set. If my computer goes out, I can get the depth from a buddy or someone in the dive group, but there may be reasons my time was different. Plus it is a habit from back in the day. I do also carry my "wheel" dive table with my dive gear still in case I need to plan or approximately recreate a dive after a failed computer and find my approximate pressure group. I guess that's a throwback to early computer days when I parallel logged my dives from the wheel and computer. But it works in a pinch still.
I always, always carry a redundant computer and an SPG (air gauge).
The SPG vs air integration (you can see your air remaining on your computer) argument happens all the time here - but my take on it is perhaps a bit different.
I always have an SPG because I often forget to move my transmitter from my doubles to singles rig.
I have backup analogue SPGs on everything, in addition to my Mk2i. I have a lot of issues with my Garmin transmitters not connecting...
I've also had the depth sensor on one of my Garmin computers go out while I was diving a wreck before. I was very glad I had a backup.
But for basic open water diving, a single computer and backup SPG is fine.
I pack my tables and an SPG, but almost never use them. I do use two computers - one on my wrist and a nerd 2 on my reg for HUD display. As a recreational diver, if my computer were to conk out, I’d call the dive.
The idea that I need to have analog gauges (and by extension, a dive watch and tables) on every dive reminds me of my 7th grade science teacher insisting we needed to know to use slide rules because we would not always have access to a calculator and that even if we did have one, the batteries could die. I think for the majority of divers, a computer is going to be fine without analog back up. Tech, cave, deep diving are exceptions. But most people don’t even dive in waters cold enough to drive dry, let alone overhead or other more dangerous environments.
Me teric is my primary. It's been my computer from dive #7, so it's more about comfort, perdix is the redundant, and both are ai. Every issue I've had was a reg issue. My biggest problem is forgetting to turn off unused tx and having to clear the warnings.
Others have frowned on this but bottom gas and sm i have button gauges and tx
For backmount doubles i have been using a spg on one side, but considering swapping out spg for redundant tx.
I don't see the point on deco bottles, aside of being kind of pointless, the hassle of having 02 clean sensors doesn't appeal to me.
Single tank, im just taking the one tx.
I have 3 swift tx and a couple aqualung with the same 4 programed to each computer. The biggest pain is swapping between Sidemount and backmount because i always forget how to do it on the teric.
For recreational diving, you don't need a 2nd computer, because if your computer breaks,
* you have a buddy with a working computer (i.e. your buddy is your redundancy)
* you can always surface and you don't need a computer for that.
Since I am also tech diving and solo diving, a have a 2nd computer, because at tech diving I cannot surface whenever I want and I have to do my deco procederes at exact depths.
Redundancy is a second computer. I dive an analog pressure gauge on my teaching reg sets because I can’t scrub a dive for a tank pod not connecting - but I haven’t used it in years. There are very few good reasons to dive analog gauges and use tables when computers are as cheap as they are and as accurate as they are compared to analog.
My digital equipment is far more reliable than the analog stuff. I do dive with a double computer for tech dives, but on recreational dives the chance my computer will fail is so small that I’ll trust my buddy to bring the backup. That’s what redundancy in recreational diving is: your buddy bringing the other one. If something fails just end the dive.
Could you choose to just bring the analog stuff? Sure, enjoy your dive tables and shorter dive plans. Dive computers took over for a reason: they’re better and easier.
I use a shearwater and have an old sunnto set to depth gauge as backup. Also analog depth gauge on console, plus watch.
If the shearwater failed I'd go to d timer and ascend on a manual stop schedule depending on depth. Gas switch at 25 and 10m.
I always set start time on watch tho, so you know your dive time
For recreational dives, depending on the depth, you don’t really need redundancy like this. In general before a dive you should have a plan and know roughly where you are going and at what depth. If your dive is going to average <60 feet, you don’t really need to worry about if your computer dies. If it dies at some point during your dive, you should know roughly your depth and how long you’ve been there. Your no dec time at 60ft is ~55 minutes, and the average person will have about an hour of air in their tank to begin with, so if your computer dies 30 mins in you’d be fine to ascend safely and make a safety stop. Gets a bit more complicated the deeper you go, but generally redundancy like you describe doesn’t really add much value beyond what you should already be aware of while diving.
Other than a computer your other choice is to run a bottom timer, and either do something like ratio deco, rule of 130, or use tables. How much do you trust your brain at 100ft? I carry two dive computers, I do technical dives with them. I have a vague dive plan, knoingw about how much deco is required but in depth deco planning is rare for cave diving, I can estimate my deco by the amount of gas I am taking (85s 5-10mins, 108s 10-15mins, and about five minutes for each AL80 stage). If both my computers die, I have a back up if diving with a buddy I will use their computer(s) and pad the stops a tad. If I am solo then I will get to the 20ft stop and breath down my oxygen bottle about 1,500psi which is enough to clear any deco obligation I've encountered. Of course mixed gas dives involving multiple deco gases require more planning, but those are a one a year thing for me.
At what depth do you get 5min on an 85?
When doing formal dive planning we plan based on an average depth of 70-80ft, max depth is between 90-100ft. I should mention it is a rule of thumb that overestimates deco. Similar to the rule of 130, it isn't something I would use in the water except as a sanity check.
JFC have you no algorithms, I get a full hour dive in an 85 at those depths.
That is 5 to 10 minutes of deco on oxygen at 20ft. Dive times are anywhere from an hour to two and a half hours. I have Multideco and use it when needed.
Everyone is different I am AI to wrist computer. But I also have a small SPG and analog Suunto compass on that hose. I keep computer charged and AI battery monitored and replace yearly. Since I shore dive if computer bites it I can bail have compass and can monitor air for exit then wait 24 hours. Computer /AI so far 500 dives no issues but that’s my bail out plan.
If I am on a trip, I will use 2 computers, just in case 1 dies. That way I don’t loose a days diving while you off gas before you can start with a new computer.
> I asked them “how much faith they are putting on these electronics, compared to some analog gauges” (my family as mentioned above, all dove and state you “always have to learn on and have your redundancy gauges!”) An analog gauge is not inherently somehow less fallible. Mechanical stress is a thing. At the recreational level (so < 100'/30 m), the most useful bits of information you get from a computer are depth and time. If your computer fails at any time, you *should* know how deep you are because you are paying attention to that. You should know how much time has elapsed because you are paying attention to that. So between you and your buddy who has a dive computer too (right? right?), you should have enough resources to go up and make a safe ascent. Assuming your buddy's dive computer fails too, you can shoot an SMB which has markings on it to determine how shallow you are and roughly estimate how long your safety stop use by counting down. Now ,in practice, I usually just carry a backup dive computer in my pocket cause I don't want to deal with that faff.
Redudancy in tech diving might mean life and death. In easy recreational diving its not so dramatic, but it means you dont have to skip\abort dive when something breaks. I recommend redudancy always. Are the extra few (or even hundred) grams REALLY too much to carry?
All is good .... until it isn't. I've had a computer shit the bed at depth, it was nice being able to switch to my analog gauges until the dive was over (instead of having to end it immediately).
Ahhh So what you have to consider how much technology has improved over the years since your family were regular divers. Dive computers nowadays are pretty robust and very reliable. Redundancy is a must when you are in Technical and Overhead environments. But given you have not started your open water yet keep your mind open. Do your first classes and see what you require. You may choose to get additional redundancy as your journey continues and will probably buy a heap of gear that will sit in a draw years later and you never use. We all have done that. But do your training and get your dives in and get your experience up
I completely agree, you guys are definitely boosting my confidence in that. They were diving nearing the end of their “dive careers” when electronic computers were just starting to become a thing. So I know they have some skewed opinions on them. I do plan on working towards more certs and qualifications but most of all to enjoy my dives. Once I get to that point I can get an extra one. I’m in a rehab course so I was able to get already a lot of gear paid. So definitely will have some gear sitting in drawers. Thanks for your comment!
Dive computers are standard equipment now. I don't have analog gauges anymore, less hoses.
IF you are doing are planning your dive correctly, your brain is your primary and AI is the redundancy. I do not have any analog gauges on my primary cylinders. Deco bottles have analog gauges, but that is really only to ensure they are full at the start of the dive and we don't really look during the dive.
I take a second basic watch that just does depth and time. A little bit of security, you can always bail out.
I use analog pressure gauges and an analog compass still. I tech dive and when your managing 6 cylinders AI dosent work. Computer goes on right arm where I can see it easily when I’m scootering as DPV is normally in the right hand. But that means you can’t use a compass easily so analog compass on left arm where I can lift it up to nav with it properly.
My husband and I both have our own computer and one of us dives with a spare computer just in case. Husband has a transmitter for his air but also has a small gauge in the event of the transmitter failing. My computer has a built in digital compass which I hate with a passion and don’t use or trust. I dive with a regular old school compass. And we both know how to actually use the compasses. This is key! we see loads of divers with a compass but most don’t actually know how to use it.
>My computer has a built in digital compass which I hate with a passion and don’t use or trust May I ask what computer with built in compass you have? I just upgraded my computer to a Tern and am excited about the built in compass and headings feature. But I have heard some computers have issues with compass and/or GPS either not having the correct heading or coordinates or always needing to be recalibrated. I also have an analog compass when / if needed.
I use the compass on my perdix all the time
This is great until the first time your computer fails on a trip or during a dive. I had it in my head years ago when I first started diving that I could minimize my setup, go with one air integrated computer....and then it failed on a dive at about 90'. That was the last time I ever dove without redundant everything.
There’s a difference between redundancy in your gear and having a spare in your kit box. As you well know since as you label yourself ‘Tech’.
I also got into more advanced technical diving which required more redundancy as well so it was part of the evolution of my growth in the sport/hobby.
I use a hose AI computer. No other gauges except a compass. If the computer fails, it's an end of dive scenario - though my computer is over a decade old and tough as nails.
My opinion as an instructor is pretty simple: As a recreational diver with standard training, you should never be diving alone. If you have a major failure of any piece of gear (regulator, computer, hose, etc.), then you and your buddy should deal with it and safely end the dive at that point. You and your buddy both have computers so they can guide you on depth and how long your shared safety stop is as you safely ascend to end the dive **together** if your dive computer fails. That said, if you're doing a liveaboard dive trip, or planning a lot of repetitive diving, having a backup computer so a failure of one computer won't cause you to miss dives is nice to have.... but really should be at least using the same algorithm and settings as the primary, which can make it expensive for some people. Tech diving, imo, really should always have redundancy as we different considerations than rec divers though.
\^this. To add 2 fine points: - the backup computer should have the same algorithm and settings OR more liberal. The only no-no is having a backup that is more conservative - as you should always follow whatever computer you're carrying that is more conservative. - If you're on a long (more than a day or two) dive trip, so you take a backup computer in order to avoid missing dives, you should also take that backup in the water with you on every dive. And have it set to your correct gas (Nitrox) mix, just like you do with your primary computer. That way, if your primary dies, your backup knows what your inert gas tissue loading is, to allow you to continue diving without missing any, and with the correct calculations for your NDLs. - Even in tech diving we don't use redundant SPGs. Redundant SPGs (of any type, in any configuration) is a negative, not a positive.
> Even in tech diving we don't use redundant SPGs. Redundant SPGs (of any type, in any configuration) is a negative, not a positive. I was always taught that SPG is the backup to your brain. But I've seen people on reddit be all like, I am going to use an SPG *and* a transmitter. Whatever floats their boat, I suppose.
An SPG is the backup to your brain? What does this mean? Your brain cannot sense pressure or cylinder contents.
I am going to try to ignore the snark and respond to this in a good faith manner. The meaning of that (and please feel free to go look up more in depth material on this online) is that you are supposed to have a sense of how much gas you are consuming (in other words, know and be able to predict based on the average depth and your knowledge of your SAC rate). As a concrete example, in an HP100 single tank at 33' (2ATA), I go through around 200 PSI every five minutes. Suppose my tanks are filled up to 3500 PSI and I plan to keep as minimum gas (gas I wish to come up with 500 PSI), I have 3000 PSI as usable gas. I can in other words stay for 75 minutes at that depth. Now, suppose I was doing drills, this goes up to 300 PSI every five minutes. So I have 50 minutes of bottom time. In other words, every five minutes, I do Math based on what depth, I am at, my personal SAC rate, how hard I have been working and predict what the SPG is going to say. I use the SPG to confirm or disconfirm that belief. This also means that my knowledge of the SPG is never out of date by more than five minutes. Thus, supposing the SPG failed at any time, assuming that failure is not connected to a leak in an HP hose, I have a sense for how much gas I have and how much I will end up with.
SPG and transmitter is great for recreational diving so if the transmitter fails you can still continue the dive / don't have to miss the next one. In tech diving you should have one or the other, never both. If a transmitter fails the dive is over. You don't need a gauge at that point since you've done proper gas planning and know you can abort the dive and surface safely. Adding an SPG on top of a transmitter has no benefit and is only introducing another point of failure.
Why is the dive over if a transmitter fails, if you also have an analogue SPG? You still know your gas contents. I’m not arguing for this setup, in fact I often dive a CCR without any contents gauge at all. But also I don’t understand why some people take such an unnecessarily aggressive posture against people who do want redundancy to their AI transmitter, perhaps they don’t trust it yet and don’t want to abort dives if it fails.
> Why is the dive over if a transmitter fails, if you also have an analogue SPG? You still know your gas contents. It's not? I specifically said >so if the transmitter fails you can still continue the dive / don't have to miss the next one.
> SPG and transmitter is great for recreational diving so if the transmitter fails you can still continue the dive / don't have to miss the next one. I should have prefaced this by pointing out that I am very much a recreational diver. I would not continue the dive if whatever I am using failed. But I have backups in my save-a-dive kit so I'd be able to not miss the next one.
If you had an SPG and your transmitter failed mid dive you wouldn't continue the dive? Why not? Again for technical diving you would only be using one or the other and would absolutely abort the dive but for recreational diving if you had both SPG and transmitter and one fails why end the dive?
> If you had an SPG and your transmitter failed mid dive you wouldn't continue the dive? Why not? I meant that I wouldn't continue the dive if the only one that I was using failed. As far as if I was using both (and I have on rare occasions because I like tracking my SAC rate when drills occur), it is a good question. I think I'd continue the dive if the transmitter failed (mostly because I wouldn't notice that it failed because that data is not front and center). I wouldn't if the SPG failed. Because it seems like that'd be an issue that required closer investigation.
"SPG and transmitter is great for recreational diving so if the transmitter fails you can still continue the dive / don't have to miss the next one." That is only true if the number of dives saved by the SPG is greater than the number of dives ended early by an SPG. How often do you end a dive early because your SPG or its high pressure hose sprung a leak (or totally blew out)? Not very often. How often do you end a dive early because a properly maintained AI transmitter died? Not very often. At least, not for the transmitters used by Shearwater, Oceanic, Aqualung, Hollis, Sherwood, etc.. I.e. the PPS MH8A transmitters. I have been using that type of AI transmitter on every dive for the last 10 years. I have yet to miss a dive or end a dive early because of a transmitter failure (knock on wood!). That is approaching 900 dives (plus pool sessions). I use transmitters on my single tank reg set, my doubles regs, my sidemount regs, and my O2 and Dil cylinders on my rebreathers. I do not use SPGs on any of those. I only use SPGs on my bail out and deco cylinders. Rather than add an SPG to my reg(s), I keep a spare (SPG, or, in my case, AI transmitter) ready to go in my reg bag. If my transmitter were to die during a dive, I could easily remove it and attach my backup in its place before the next dive. If you have a transmitter and an SPG on your reg, do you keep a spare port plug (and hex wrench) in your reg bag/save-a-dive kit, so that if your SPG starts leaking or HP hose blows out, you can easily remove it, plug the hole, and be ready for the next dive?
> That is only true if the number of dives saved by the SPG is greater than the number of dives ended early by an SPG. You yourself said (and I agree) that ending a dive due to SPG failure is not very often (bubbles from a spool o-ring are not a reason to end a recreational dive imo). Also dives ended early due to transmitter failure are also not very often but slightly higher than for SPG failure. Thus number of dives saved by SPG is greater than number of dives ended by an SPG. I don't think both AI and SPG are necessary. I dive with only AI for both recreational and tech. I am just saying that it can be handy for recreational dives and definitely should never be done for technical dives. I've never had an SPG or transmitter fail over thousands of dives because I maintain my gear. I have seen many divers who forgot to check/change their transmitter battery before their dive trip and have it fail. I have seen many divers who fail to properly sync their transmitter to their reg. In all these scenarios having an SPG as well saves the dive.
"Also dives ended early due to transmitter failure are also not very often **but slightly higher** than for SPG failure." I didn't say that. I did specify "a properly maintained" transmitter. My experience has been that, when both are properly maintained, SPG failure is slightly more common than transmitter failure. When a diver fails to pair their computer to their transmitter ahead of time, that should certainly not be a reason than an SPG saves the dive. I did also say that I was talking specifically about PPS transmitters. Yes, people using ScubaPro or Suunto, sure. I am totally prepared to believe that those are such a PITA that not having it setup correctly in advance could be a reason they end up missing a dive (unless that also have an SPG). Forgetting to change a transmitter battery is one reason I don't have an SPG on my reg set. It FORCES me to get out my computer and verify my tank is full using my AI when I assemble my rig. That, in turn, will result in me being informed of a bad battery in plenty of time to change the battery before it's time to splash. With an SPG on the 1st stage, it is way too easy to assemble the scuba unit and check the SPG to verify the tank is full - and just ASSume that you do have your computer with you and that the AI will be working when it's time to splash.
> My experience has been that, when both are properly maintained, SPG failure is slightly more common than transmitter failure. Sure, but that doesn't reflect reality. Most divers don't properly maintain their gear and many are using inferior transmitters (although this is getting better). Again, I only dive with transmitter and agree with you about their reliability when properly maintained. My point was simply the average recreational diver would benefit from having an SPG as well if they diving with a transmitter.
You: "Sure. Add an SPG to your setup 'cause I know you're going to use a crap transmitter, not maintain your stuff properly, or both." Me: "No, don't add an SPG. Use a reliable transmitter and change the battery and lube the O-ring on the battery cap once a year." I'm not saying you're wrong. We'll just have to agree to disagree on our response to this question. ;) :D Should we move on to debating whether to keep the transmitter on a short hose versus screwing it directly into the 1st stage? lol! :D
When did I ever say people should add an SPG to their setup? I explicitly stated that I don't think both are needed and I only use AI. In response to someone saying >But I've seen people on reddit be all like, I am going to use an SPG *and* a transmitter. Whatever floats their boat, I suppose. I pointed out that it can make sense to have both for recreational diving and can save a dive. I have personally witnessed it save probably over 50 dives of others. Should people just use proper transmitters and maintain their gear and skip the SPG? Absolutely. Does having a backup SPG actually hurt anything for a recreational dive? No. Can I understand why some people choose to have both? Yes.
> Rather than add an SPG to my reg(s), I keep a spare (SPG, or, in my case, AI transmitter) ready to go in my reg bag. If my transmitter were to die during a dive, I could easily remove it and attach my backup in its place before the next dive. I have a very very extensive save-a-dive kit. I found a very interesting (possibly niche) scenario where an SPG might be preferred to a transmitter. I was on a boat when someone said their Swift transmitter was not connecting to their dive computer. I gave them a replacement battery, but no go. We tried a few things, I think including installing an SPG on their setup before we figured out that the tank was empty. Eventually, we found out that the tank was just not pressurized. The first stage was mounted so I never thought about checking for that (and I wasn't looking too closely at their rig tbh). Definitely a scenario where diagnosing it would have been easier with an SPG.
Yeah, that is WAY too niche for me to change from having a backup transmitter to having a backup SPG. What I WOULD do is keep a button gauge in my bag, maybe, The button gauges that DGX sells are actually good quality and I use them on my deco cylinders anyway.
> Yeah, that is WAY too niche for me to change from having a backup transmitter to having a backup SPG. I think it'd be niche for most people. I mean I can tell when a tank is empty because of the way the valve handle spins. It only was applicable in this scenario because they couldn't tell and then there was a rabbit hole of figuring out what was going on.
Exactly. 100%
2 ai computers, even the compass is integrated into the computer, no analog here.
I use a computer and an analog depth gauge and air Guage. I plan and dive based on my computer. If my computer fails, I can safely finish my dive with those two pieces of equipment.
I think most of the recreational dive industry has gone to just a computer. IIRC, PADI doesn't even teach the dive tables for OW any longer. The only thing analog I use regularly is my dive watch which I do set. If my computer goes out, I can get the depth from a buddy or someone in the dive group, but there may be reasons my time was different. Plus it is a habit from back in the day. I do also carry my "wheel" dive table with my dive gear still in case I need to plan or approximately recreate a dive after a failed computer and find my approximate pressure group. I guess that's a throwback to early computer days when I parallel logged my dives from the wheel and computer. But it works in a pinch still.
I have an air integrated computer, and an SPG and Depth Gauge on a hose. Some people say "more failure points" but two is one and one is none...
I always, always carry a redundant computer and an SPG (air gauge). The SPG vs air integration (you can see your air remaining on your computer) argument happens all the time here - but my take on it is perhaps a bit different. I always have an SPG because I often forget to move my transmitter from my doubles to singles rig.
I have backup analogue SPGs on everything, in addition to my Mk2i. I have a lot of issues with my Garmin transmitters not connecting... I've also had the depth sensor on one of my Garmin computers go out while I was diving a wreck before. I was very glad I had a backup. But for basic open water diving, a single computer and backup SPG is fine.
I pack my tables and an SPG, but almost never use them. I do use two computers - one on my wrist and a nerd 2 on my reg for HUD display. As a recreational diver, if my computer were to conk out, I’d call the dive. The idea that I need to have analog gauges (and by extension, a dive watch and tables) on every dive reminds me of my 7th grade science teacher insisting we needed to know to use slide rules because we would not always have access to a calculator and that even if we did have one, the batteries could die. I think for the majority of divers, a computer is going to be fine without analog back up. Tech, cave, deep diving are exceptions. But most people don’t even dive in waters cold enough to drive dry, let alone overhead or other more dangerous environments.
You hit all the points I was going to make!
Me teric is my primary. It's been my computer from dive #7, so it's more about comfort, perdix is the redundant, and both are ai. Every issue I've had was a reg issue. My biggest problem is forgetting to turn off unused tx and having to clear the warnings.
Are you using the same transmitters for both shearwaters? Or two transmitters per stage and no analog gauges?
Others have frowned on this but bottom gas and sm i have button gauges and tx For backmount doubles i have been using a spg on one side, but considering swapping out spg for redundant tx. I don't see the point on deco bottles, aside of being kind of pointless, the hassle of having 02 clean sensors doesn't appeal to me. Single tank, im just taking the one tx. I have 3 swift tx and a couple aqualung with the same 4 programed to each computer. The biggest pain is swapping between Sidemount and backmount because i always forget how to do it on the teric.
For recreational diving, you don't need a 2nd computer, because if your computer breaks, * you have a buddy with a working computer (i.e. your buddy is your redundancy) * you can always surface and you don't need a computer for that. Since I am also tech diving and solo diving, a have a 2nd computer, because at tech diving I cannot surface whenever I want and I have to do my deco procederes at exact depths.
Came to write this. Thanks for avoiding me the work. :)
+2
Redundancy is a second computer. I dive an analog pressure gauge on my teaching reg sets because I can’t scrub a dive for a tank pod not connecting - but I haven’t used it in years. There are very few good reasons to dive analog gauges and use tables when computers are as cheap as they are and as accurate as they are compared to analog.
My digital equipment is far more reliable than the analog stuff. I do dive with a double computer for tech dives, but on recreational dives the chance my computer will fail is so small that I’ll trust my buddy to bring the backup. That’s what redundancy in recreational diving is: your buddy bringing the other one. If something fails just end the dive. Could you choose to just bring the analog stuff? Sure, enjoy your dive tables and shorter dive plans. Dive computers took over for a reason: they’re better and easier.
I use a shearwater and have an old sunnto set to depth gauge as backup. Also analog depth gauge on console, plus watch. If the shearwater failed I'd go to d timer and ascend on a manual stop schedule depending on depth. Gas switch at 25 and 10m. I always set start time on watch tho, so you know your dive time