Backup Computer Recommendations?

[Fedaykin]

It is good to see people who can afford to have a back-up for everything and letting all of the calculations done by machines. It is unbelievable how people managed to dive without dive computers… Sorry for annoying a diving guru like you with my inexperienced, poor way of thinking…

What you "don't see" is probably due to significant inexperience and/or knowledge deficit in technical diving principles and practices.

 

[Stoo]

As tbone pointed out, carrying a computer in gauge mode is only helpful if you are carrying tables, and even then, unless you have been plotting your repetitive N2 along the way, it isn't going to a lot of help.

I agree that two computers that are the same is the best option, but in the case of a Petral, kinda pricey.

My wife wears two pucks and I have one as a backup. We have tweaked my Petral GFs to be "similar" to the others so I keep my puck in deco mode and just follow whichever one is the most conservative.

When the next puck dies, we'll likely replace it with another Petral...

 

[RyanT]

It is good to see people who can afford to have a back-up for everything and letting all of the calculations done by machines. It is unbelievable how people managed to dive without dive computers… Sorry for annoying a diving guru like you with my inexperienced, poor way of thinking…

To be clear, conducting your own calculations (aka tables) is different from just "staying with the group." Diving another diver's computer is a really bad idea. Back to the OP, I use a DG03 as a backup. It's not really my favorite, but it is compact, can be run in gauge mode, and does the job. I would consider it again as a back up.

 

[Stoo]

It is unbelievable how people managed to dive without dive computers… Sorry for annoying a diving guru like you with my inexperienced, poor way of thinking…

Are you of the camp that thinks that tables are somehow more accurate or "safe" than computers? I've never understood this (and I dove extensively using tables for close to 15 years and was involved in testing one of the first electronic computers). Tables were based on real-life experimentation and then computer simulations. The main reason that tables can me more "safe" than computers is that the calculations are based on square profiles, whereas most dives are not.

I was doing liveaboards in the late '70s and early '80s where we used to run profiles where we (according to the tables) were so saturated with nitrogen that we could barely take a shower without risking getting bent! Of course in hindsight, I know that we were being ridiculously conservative and wasted hours of bottom time, given our profiles.

It's very trendy to "dis" computers, but after 43 years of diving and well over 5000 dives, I am comfortable in saying that dive computers are the single greatest development in diving since the regulator. They aren't perfect, mostly in the failure department, but that's not because the logic behind them but because of poor manufacturing designed to keep the price point attractive. Just look at Shearwater... They have built what appears to be a bomb-proof computer line, but it's expensive as a result.

 

[stuartv]

Are you of the camp that thinks that tables are somehow more accurate or "safe" than computers? I've never understood this

...

I am comfortable in saying that dive computers are the single greatest development in diving since the regulator.

I have very limited experience, but I would still be inclined to agree with your last statement.

But, on the first statement, I would agree that tables are not more accurate than a computer, but how can you argue that tables are not more safe?

We're talking about recreational sport diving, right? I.e. NDL diving. If you use a table (correctly), from what I can tell, it will almost always get you out of the water sooner than any recreational computer, won't it? Isn't that safer? The only time a computer will get you out of the water sooner is if you dive a perfectly square profile to an exact depth that is on a table (i.e. in Imperial units, to a depth that is an exact multiple of 10). I.e. virtually never.

Caveat: My statement could be very wrong, if you compare tables to what a conservative computer would do when used in conjunction with a cranked up Conservatism Factor. In that case, maybe the computer would give you less time in the water than a table would, even for not-perfectly-square profiles. I don't know. But, in that case, I don't know that there's much meaning in saying either way is "safer" than the other. Tables or a conservative computer with an elevated Conservatism Factor - either way, it's a, statistically, very safe way to do NDL diving.

To me, the benefit of computers is that they are more accurate, so they allow you more time in the water while still being acceptably safe. It's a huge benefit. But, it seems to me that diving tables (for NDL diving) would pretty much always be safer - by being overly conservative.

 

[Stoo]

The only reason that tables "may" be safer is because they are based on square profiles. So if you did say, a 100' dive, and the tables said you had a max NDL of 12 minutes, and you stuck to this, and added in a 3 min safety stop, that's acceptable, straight down a line, swim around at 100', then back up the line. It is not especially "safe" though...and most computers will closely mimic the table.

On the other hand, if you do a "100 foot" dive on a reef, most likely, you will hit max depth and then start to work your way back up. A computer will constantly give you "credit" for that time working your way up, and you can very likely spend an hour or more and still never get near your NDL. The "safety" of the table comes from the fact that you missed out on 60 - 12 minutes of diving.

If you have read anything about US Navy tables, you will understand that they were developed with a certain amount of failure allowed... folks getting bent... because it was deemed to be an operational necessity. (And since there was likely a chamber close by, not too big of a problem.) Updated tables are considerably more conservative than USN tables of course.

To me, the benefit of computers is that they are more accurate, so they allow you more time in the water while still being acceptably safe. It's a huge benefit. But, it seems to me that diving tables (for NDL diving) would pretty much always be safer - by being overly conservative.

Agreed... But since I want to maximize my time in the water, whenever possible, I will only end the dive when I am racking up an unacceptable amount of decompression (which could be "0" minutes, or more...) or my gas supply is running low.

 

[savsuds]

kcprofessor,

What sort of diving are you doing on your trip? Because the biggest requirement you are asking for is that it does not lock out and can be used as a back-up. If you are not exceeding your NDL, then adjusting the Petrel GF to match the Suunto HelO2 conservatism is really one of your cheapest alternatives. The other cheap route is borrowing a friend's computer like was previously mentioned.

Now if you plan to exceed NDL limits, then you would require a different back-up computer. That would rule out Suunto and PPS dive computers. I believe they all have a lock-out of 48-24 hours respectively.

Is there some sort of diving you might need a more advanced back-up dive computer coming up after your trip? It may help save you money in the long run to just buy more computer now than you need for the trip, to prevent an additional purchase down the road.

Also, you did not list a price ceiling.

Others here can chime in recommendations once you provide a bit more information. We are only going to spin our wheels without more information from you.

 

[Stoo]

kcprofessor,

What sort of diving are you doing on your trip? Because the biggest requirement you are asking for is that it does not lock out and can be used as a back-up. If you are not exceeding your NDL, then adjusting the Petrel GF to match the Suunto HelO2 conservatism is really one of your cheapest alternatives. The other cheap route is borrowing a friend's computer like was previously mentioned..

I agree with this. The odds of the Petral failing are very small. I always change the battery before a trip, and ideally do one dive on it before I go...

 

[kcprofessor]

What sort of diving are you doing on your trip?

To answer your question about the sort of dives, they will be in the 130 foot to 180' depth range with lots of wreck penetrations. Planned deco on almost all of the dives as we will be wanting to maximize bottom time. All dives will be planned. A non-redundant computer setup won't be a problem during the dive as I can simply abort the balance of the bottom time and follow the planned deco schedule. The obvious problem comes in after I get back on the boat and have to sit out until I am totally free of residual nitrogen. I could then use either dive tables or dive planning software. No matter how you look at it, a computer failure means a minimum of 24 hours on the deck watching others dive.
So, after reading all of the suggestions, I am still undecided. I don't want to hobble the Petrel by experimenting with gradient factors until I match the backup, so my options are probably a Nitek Q or hope I can find a used Shearwater. I would like to keep the cost under $500 since that's about what a day of diving costs.

 

[stuartv]

That would rule out Suunto and PPS dive computers. I believe they all have a lock-out of 48-24 hours respectively.

Huh? Isn't my Oceanic Atom a PPS computer?

I have gone into deco on it numerous times. The deco on it always clears by the time I actually get out and it doesn't lock me out.

Regardless of whether Oceanic are PPS or not, as far as I know, no computer will lock you out unless you go into deco AND skip the stops it tells you to do. The only problem with going into deco on something like a Suunto (from what little I know) is that it will give you longer deco stops and shorter NDLs on repetitive dives after that, as compared to other computers.