Gear Advice for Novice Divers From Novice Diver

[rongoodman]

Weird. I've never heard of a computer which didn't show at minimum the current depth and dive duration. What brand/model is it?

 

[stuartv]

@stuartv, ok i get it... have you see another diver run the same set-up? Again, just curious, not trolling...

No, but I can't say that I generally look that closely at other people's rigs. I mean, not closely enough to note whether they have a button gauge on their 1st stage.

 

[jlcnuke]

Just to be clear, I think there are pros and cons to AI with a button gauge. I think it's really down to personal preference. EDIT: Just make sure if you use a button gauge, it is one of good quality.

The one configuration I would actually argue against is using AI AND an actual SPG. To me, that is more potential for a dive-ending failure with no significant benefit. Pick one or the other. AI or an SPG. Just not both.

I've been running AI and a SPG for the past 2 years. If my SPG fails, but my AI is still working, then there's no reason for me to end the dive (just like you wouldn't end the dive just because you only had one reliable indicator of pressure. I'd much rather be able to keep diving if the battery in my transmitter dies (or otherwise stops working) personally, than avoid the potential for a leak going to my SPG causing me to end a dive.

 

[stuartv]

I've been running AI and a SPG for the past 2 years. If my SPG fails, but my AI is still working, then there's no reason for me to end the dive (just like you wouldn't end the dive just because you only had one reliable indicator of pressure. I'd much rather be able to keep diving if the battery in my transmitter dies (or otherwise stops working) personally, than avoid the potential for a leak going to my SPG causing me to end a dive.

If you didn’t have AI, would you dive with 2 SPGs?

 

[jlcnuke]

If you didn’t have AI, would you dive with 2 SPGs?

Nope, because I can't have the 2nd SPG nice and conveniently located on my wrist.. the fact that I can dive with an AI computer and an SPG without inconveniencing myself AND getting that redundancy at the same time makes it worth it to me. I also dive with 2 computers though (only one AI normally on my rec dives, though that might change now that I've picked up a Perdix AI as well), and I'd similarly continue a recreational dive if one of them failed.

Upside of redundancy on rec dives - I don't have to thumb the dive for a single failure. Downside is.... I have to have redundancy that doesn't bother me at all??

 

[stuartv]

Nope, because I can't have the 2nd SPG nice and conveniently located on my wrist.. the fact that I can dive with an AI computer and an SPG without inconveniencing myself AND getting that redundancy at the same time makes it worth it to me. I also dive with 2 computers though (only one AI normally on my rec dives, though that might change now that I've picked up a Perdix AI as well), and I'd similarly continue a recreational dive if one of them failed.

Upside of redundancy on rec dives - I don't have to thumb the dive for a single failure. Downside is.... I have to have redundancy that doesn't bother me at all??

If you can have an SPG on one side with no inconvenience, surely could have one on the other side without inconvenience? Why is redundancy important to you for AI, but not a physical SPG?

 

[jlcnuke]

If you can have an SPG on one side with no inconvenience, surely could have one on the other side without inconvenience? Why is redundancy important to you for AI, but not a physical SPG?

There's a difference between it "being important" and being convenient. There is absolutely no inconvenience imo for me to use what I have already (had SPG already, trained to use it in the configuration it's in, so absolutely no reason to get rid of it when I "got" AI as well).

I was trained to use an SPG in rec diving. I'm fairly certain that my tec diving training wants me to do the same (well, 100% certain). I've also been trained to use a computer, whether AI or not. I see no reason to change my gear configuration to eliminate a SPG simply because I happen to have an AI computer being used as well. The added bonus of "I can still see my pressure and keep diving if there's a failure of my AI" is a bonus. Though yes, there is the added inconvenience of still having to take a second to clip it on/off when setting up gear...

If we're both diving and both of our AI transmitters lose signal/battery dies/etc, your dive is over. Mine isn't because I have a backup. Missing out on a dive seems like a bigger inconvenience than using an SPG for me. Perhaps clipping a SPG off is a massive hassle for you though, and you'd rather miss out on some dive time than have to deal with such a 1 second evolution repeatedly or the astronomically low chance that your hose that you take proper care of has an issue during a dive. To me, it's such an easy task that I do it automatically already and see no need to stop. To each their own.

 

[stuartv]

There's a difference between it "being important" and being convenient. There is absolutely no inconvenience imo for me to use what I have already (had SPG already, trained to use it in the configuration it's in, so absolutely no reason to get rid of it when I "got" AI as well).

I was trained to use an SPG in rec diving. I'm fairly certain that my tec diving training wants me to do the same (well, 100% certain). I've also been trained to use a computer, whether AI or not. I see no reason to change my gear configuration to eliminate a SPG simply because I happen to have an AI computer being used as well. The added bonus of "I can still see my pressure and keep diving if there's a failure of my AI" is a bonus. Though yes, there is the added inconvenience of still having to take a second to clip it on/off when setting up gear...

If we're both diving and both of our AI transmitters lose signal/battery dies/etc, your dive is over. Mine isn't because I have a backup. Missing out on a dive seems like a bigger inconvenience than using an SPG for me. Perhaps clipping a SPG off is a massive hassle for you though, and you'd rather miss out on some dive time than have to deal with such a 1 second evolution repeatedly or the astronomically low chance that your hose that you take proper care of has an issue during a dive. To me, it's such an easy task that I do it automatically already and see no need to stop. To each their own.

I'm not trying to be argumentative. I'm just trying to discuss the merits of the different options. If you don't care to discuss, that's fine and I'll shut up.

You said: "f we're both diving and both of our AI transmitters lose signal/battery dies/etc, your dive is over. Mine isn't because I have a backup."

And I say "if your SPG springs a leak, your dive is over, whether you have AI or not."

You mentioned that there is a low chance your hose on an SPG, that you take proper care of, will have an issue during a dive.

I agree. I also think that if you do proper maintenance on your AI transmitter, it has an even smaller chance of an issue. Further, if your transmitter does have an issue, there's just about zero chance it will result in losing gas. But, if your SPG has an issue, then it is entirely possible that you will be losing gas. So, an item that you don't even normally use or plan to use (your SPG) could have a failure that results in ending the dive.

I *think* that the reason you wouldn't use a redundant SPG, in the case that you were not using AI, is that you feel like the chance of a problem with an SPG is so low that you are not worried about it. What I'm saying is that a PPS transmitter (as used by your Shearwaters and that you take proper care of, including battery changes per the maintenance schedule) has EVEN LESS of a chance of an issue. I don't have a scientific study to back that up. That is just my sense of the current state of the technology from my own anecdotal experience plus what I've seen when out diving.

So, if an SPG doesn't merit redundancy, why does an even more reliable device merit redundancy?

I didn't ditch the SPG off my rigs because it's inconvenient. I ditched it because I never did and have never needed to look at it whereas I HAVE had an SPG blow out (specifically, a spool O-ring).

There is a good chance I would not end my dive particularly early if my AI transmitter did die. I plan my dive. I know my consumption. Most of the dives I do, I KNOW that I'll hit my NDL before I get low on gas, or I KNOW that I will hit my planned max time before I get low on gas. Ending a dive prematurely because of an AI failure is low probability, even if the transmitter dies (which is EXTREMELY low probability).

I definitely would not be happy to end a dive early because something I'm not even planning to use (a redundant SPG) had an issue.

 

[jlcnuke]

I'm not trying to be argumentative. I'm just trying to discuss the merits of the different options. If you don't care to discuss, that's fine and I'll shut up.

You said: "f we're both diving and both of our AI transmitters lose signal/battery dies/etc, your dive is over. Mine isn't because I have a backup."

And I say "if your SPG springs a leak, your dive is over, whether you have AI or not."

You mentioned that there is a low chance your hose on an SPG, that you take proper care of, will have an issue during a dive.

I agree. I also think that if you do proper maintenance on your AI transmitter, it has an even smaller chance of an issue. Further, if your transmitter does have an issue, there's just about zero chance it will result in losing gas. But, if your SPG has an issue, then it is entirely possible that you will be losing gas. So, an item that you don't even normally use or plan to use (your SPG) could have a failure that results in ending the dive.

I *think* that the reason you wouldn't use a redundant SPG, in the case that you were not using AI, is that you feel like the chance of a problem with an SPG is so low that you are not worried about it. What I'm saying is that a PPS transmitter (as used by your Shearwaters and that you take proper care of, including battery changes per the maintenance schedule) has EVEN LESS of a chance of an issue. I don't have a scientific study to back that up. That is just my sense of the current state of the technology from my own anecdotal experience plus what I've seen when out diving.

So, if an SPG doesn't merit redundancy, why does an even more reliable device merit redundancy?

I didn't ditch the SPG off my rigs because it's inconvenient. I ditched it because I never did and have never needed to look at it whereas I HAVE had an SPG blow out (specifically, a spool O-ring).

There is a good chance I would not end my dive particularly early if my AI transmitter did die. I plan my dive. I know my consumption. Most of the dives I do, I KNOW that I'll hit my NDL before I get low on gas, or I KNOW that I will hit my planned max time before I get low on gas. Ending a dive prematurely because of an AI failure is low probability, even if the transmitter dies (which is EXTREMELY low probability).

I definitely would not be happy to end a dive early because something I'm not even planning to use (a redundant SPG) had an issue.

See, I guess the major difference between us is what failures we consider more likely. As the transmitter and computer must keep signal, and neither transmitter nor computer must have a failure, to me seems like a system more likely to encounter a failure than a mechanical SPG on a hose. As such, I find the hose and SPG "feels" more reliable to me (of course, I always have a backup computer as well and don't have hard data on the failure rates of either to verify that feeling).

I come from the nuclear submarine world, and we tend to stick with the "tried and true" long after "most people have accepted the new stuff is acceptable". You don't feel that a failure of the AI is a real concern and feel that an SPG is more likely to fail. I don't agree, possibly because I trust the "old school technology", possibly because you've had an SPG failure and I haven't, possibly because I've seen an AI computer drop the connection to its transmitter and need it reprogrammed in before it would work again and you probably haven't, possibly I'm still gun-shy of putting all my trust in an AI connection from the frequency of dropped signals over the years.

Personally, if I had no way to tell how much pressure I have in my tank (other than what I think it "should" have in it), I'm ending the dive immediately whether I planned to finish the dive at 500 psi or 2,000 psi based on the dive plan. Different strokes for different folks.

 

[stuartv]

See, I guess the major difference between us is what failures we consider more likely. As the transmitter and computer must keep signal, and neither transmitter nor computer must have a failure, to me seems like a system more likely to encounter a failure than a mechanical SPG on a hose. As such, I find the hose and SPG "feels" more reliable to me (of course, I always have a backup computer as well and don't have hard data on the failure rates of either to verify that feeling).

I come from the nuclear submarine world, and we tend to stick with the "tried and true" long after "most people have accepted the new stuff is acceptable". You don't feel that a failure of the AI is a real concern and feel that an SPG is more likely to fail. I don't agree, possibly because I trust the "old school technology", possibly because you've had an SPG failure and I haven't, possibly because I've seen an AI computer drop the connection to its transmitter and need it reprogrammed in before it would work again and you probably haven't, possibly I'm still gun-shy of putting all my trust in an AI connection from the frequency of dropped signals over the years.

Personally, if I had no way to tell how much pressure I have in my tank (other than what I think it "should" have in it), I'm ending the dive immediately whether I planned to finish the dive at 500 psi or 2,000 psi based on the dive plan. Different strokes for different folks.

It's not just how likely we consider the failures to be. It's how we are breaking down the possible failures and how important we consider them.

Is it possible that my computer and transmitter will lose connection during a dive? Yes. But, it has never happened for more than 1 - 2 seconds. If I look at my computer and it takes 1 or even 2 seconds to reconnect and show me my tank pressure, that doesn't bother me at all. You seem to be taking that as a dive-ending failure.

I use 2 computers that both read the same transmitter. So, if one computer dies, I still haven't lost my SPG.

I have heard of computers that totally lose their connection to their transmitter and have to be reprogrammed before it works again. But, I have never heard of that for a computer that reads the type of transmitter that Shearwater uses. Have you? I don't think it's really possible, because of the system design for the PPS transmitter (that Shearwater and others use).

You also did not address the issue that I raised regarding gas loss from failures. If my transmitter battery dies, I'm not going to lose any gas. I might end my dive, but it does not turn into an emergency. If your hose gets cut or ruptures or a spool O-ring blows out, you have a potential emergency on your hands.

With your experience as a nuke, surely you have seen things where the Navy was slow to adopt something that was obvious to everyone was actually an improvement...? Is that always a good thing?

Bottom line, these are the ways I would possibly not know what my tank pressure is:

- transmitter battery dies - I replace the battery per the maintenance schedule and that is a non-concern. My CCR only has one battery in it. Am I really going to not dive something just because one battery COULD die? No. That's what checklists and maintenance schedules are for.

- BOTH my computers die - a non-concern.

- I had a momentary loss of connection - it happens, but it always comes back within 1 second or so. A non-concern.

- transmitter floods or otherwise just craps out - given proper maintenance, this seems to be even less likely than an SPG spool blowout.

So, to me, given how unlikely it is to really have a dive-ending problem with a PPS/Shearwater transmitter, adding an SPG is just adding something else to my rig that could cause a problem. And if it does, it's most likely to be a problem that involves losing gas, which could turn into an emergency.

Steve Lewis (aka @Doppler) says in his book, The Six Skills, that part of being streamlined in the water is not taking things with you that you don't need. To ME, when you have a PPS transmitter and 2 computers to read it, a physical SPG is one of those things that you don't need and the concept of being streamlined dictates that you leave it on the boat.

My gut says that you are more likely to end a dive because of some issue with your redundant SPG than you are because a PPS transmitter simply crapped out. But, it is certainly the case either one could happen. Or, in your case, both could happen - on the same dive, even.

ps. I am definitely not saying that I would never end a dive early if my transmitter died. If it's a technical dive, then the dive is over, period. Thems the rules. If it's a recreational dive, then there are a lot of dives I do where I would not end it early. Some where I would end it early, but not immediatley, just to err on the side of caution. And some where I would end it immediately. It just depends on the specific circumstances.