Am I the only one that dives with 2 computers?

[tbone1004]

why I always try to talk to people about their long term diving goals to make sure that they don't have to relegate computers to the shelf or try to sell them. I.e. if you want to do technical diving or have any interest in it, the Zoop should be one of the last computers you ever look at as a backup, but most of higher up Suunto's are OK because they at least have gauge mode which allows you to run tables with them as a backup.

Most of the algorithms are very close to each other at deeper depths, 80+ft, but shallower than that is where I've seen the most discrepancy, up to 5 minutes was about the largest gap I can recall. Was between a Suunto Zoop and a Nitek Duo I think. The bigger issue with Suunto comes in when you have sawtooth profiles, short SIT's and all of the other things that people have said cause them to lose significant NDL's without warning where a computer that is running a straight algorithm will just continuously track.

 

[Water Boy76]

Just this weekend was a perfect example of why I dive with two computers. My third drop of the day I accidentally turned Nitrox default 50 to "ON" while changing F02 my primary. I had a new diver on the boat and was more worried about her computer that mine. Damn thing wen't crazy on me at 60 feet on descent. I disregarded my primary and used my backup that was set correctly. Best dive of the day and filled my stringer. If I didn't have a backup I would have to abort the dive.

Backups are always worth it. Also, carry extra batteries for both your computers on the boat.

 

[BRT]

Always carry two computers on a trip but only dive with one. I've never had a computer fail but if it did it would be no big deal. I'd just end the dive and grab my other computer for the next dive.

If you just start swapping out computers every dive you can get some amazing bottom times!

 

[RJP]

The bigger issue with Suunto comes in when you have sawtooth profiles, short SIT's and all of the other things that people have said cause them to lose significant NDL's without warning...

Suuntos certainly don't like divers who misbehave. (I've found the main thing it doesn't like is rapid ascents... especially on deeper dives.) Though perhaps divers who misbehave oughta have a "more conservative" computer?

---------- Post added September 8th, 2015 at 04:53 PM ----------

If you just start swapping out computers every dive you can get some amazing bottom times!

We had a guy dive with us years ago who brought two computers.... one for the first dive, and one for the second. Why?

"There's something wrong with THIS one... it always beeps at me during the second dive. So now I just switch computers between dives."

Yeah. We had him switch dive boats, too.

 

[stuartv]

In the real world you might see a one minute difference on a recreational dive with a run time of 35min.

This report used a hyperbaric chamber to simulate real world dives.

http://www.scubaboard.com/forums/re...cubaLab-Computer-Test-September-2014-data.pdf

As one example, on dive 3, at 36" run time and a depth of 40', there are 5 computers showing an NDL of 53 minutes or more, with 8 or so computers showing an NDL of less than 30 minutes, and one showing an NDL of 2 minutes.

What makes this test so different than the real world? I mean, I seriously don't understand. It seems like a legitimate way to compare computers and get data that would match the real world very closely. Can you please explain why these results are so wildly different than "the real world"? The profiles for dives 1, 2, and 3 all look pretty reasonable. None of them even have any point where they ascend and then descend again. Dives 1 and 3 are a descent and then a gradual ascent. Dive 2 is a descent, pause, further descent, pause, further descent, pause, then a gradual ascent. But, none are a sawtooth (as I understand the term, anyway).

So, what is the flaw in this testing and data?

ps to the OP: I have only done Rec dives, so far, and I have pretty much always dived with a just-as-capable 2nd computer as backup, for the same reasons you mentioned. I don't want to lose any bottom time due to having to abort a dive-in-progress or to having to fall back on tables for subsequent dives.

 

[BRT]

Ridiculous...
Figure a square profile, pad the surface interval, and run it on tables with the appropriate group. Amazing that this stuff has been forgotten, hilarious even.

Geez, you guys realize we used to dive WITHOUT computers at all right? You're telling me you can't go backward because the computer fails in the middle of a dive instead of starting a dive without one? Wow.

Get your max depth from your buddy, known depth of the sight or from the sonar on the boat, you know how long you went down for, boat captains and mates are tracking this, as well as your dive buddy. Depth and time, that's all you need. Geesh.

So your max depth was 115 feet. You checked your buddies computer when yours failed and the time was 50 minutes. What group does that put you in for the next dive in an hour?

 

[RJP]

So your max depth was 115 feet. You checked your buddies computer when yours failed and the time was 50 minutes. What group does that put you in for the next dive in an hour?

Was 50 min total run time?
Was this dive #1 of the day?
Was this a recreational dive?
What gas were you breathing?

Obviously assuming a 50min bottom time with a square 115ft profile is going to give a major deco obligation. (V-Planner says 48min of deco on 28% for a 50min bottom time at 115ft)

However, with the buddy's computer it would be very easy to run dive #1 through V-Planner as a multi-level dive, set SI time, and then plan and conduct any subsequent dives.

 

[TMHeimer]

I use one with tables backup. Am not into tech. and don't recall seeing anyone else on boats with two. But I rarely take charters and I'm sure I missed some with 2.

 

[gopbroek]

What model is that? I usually need to manually track the amount of ridicule I get during a dive trip.

Auto type correct sucks, have edited

 

[RJP]

This report used a hyperbaric chamber to simulate real world dives.

http://www.scubaboard.com/forums/re...cubaLab-Computer-Test-September-2014-data.pdf

As one example, on dive 3, at 36" run time and a depth of 40', there are 5 computers showing an NDL of 53 minutes or more, with 8 or so computers showing an NDL of less than 30 minutes, and one showing an NDL of 2 minutes.

I was only commenting on "the real world" of diving with a Suunto... I have no real world familiarity with any of the other computers in the test.

What makes this test so different than the real world? I mean, I seriously don't understand. It seems like a legitimate way to compare computers and get data that would match the real world very closely. Can you please explain why these results are so wildly different than "the real world"?

I don't have the time or inclination to run the V-Planner tables for all of the dives and computers, but from a quick glance at the given profiles it seems that for a dive like #3 that gas supply, not NDL is going to be the rate limiting factor for everyone but the poor schlub diving the Cressi.

So in the artificial world of this study at 36min into the dive assume my buddy and I are at 40ft. My computer says I have 21min of NDL and my buddy has a Lynx... which says he still has 72min of NDL remaining. But in the real world, neither of us have enough gas to spend 72 more minutes at 40ft... so what's the practical difference?

EDIT - I quickly ran their Dive #3 through V-Planner, and with a good SAC rate it would take 97cf of gas to run that dive to the end of the Suunto NDL at 40ft. Wanna max out the 72 extra min of NDL that the Lynx gives you? You'll need 160cf of gas. Wanna be conservative and assume you're planning appropriate reserves... that'd be 129cf and 212cf of gas respectively. (I'm hungry for dinner, so maybe my math is off. Feel free to check my work.)

Imagine that your company gave you an extra week of paid vacation on December 31st... but told you that you had to use it by the end of the year. Sounds great hypothetically, but the reality is that it's a meaningless gesture.

That's "the real world" for ya.