Need backup computer advice please

[donnad]

We have a trip coming up and want to get a backup computer...........just a wrist model with nitrox capability. Husband has an Aeris Elite T3 and I have the Aeris XR2. So we've been on the same algorithm. So we should have the backup be the same algorithm, right??? I was looking at the Mares Puck maybe or the Aeris Manta?? Trying to keep the cost down on this. Help please. Thanks in advance.

 

[CT Sean]

My personal, totally unprofessional, opinion is that it's rather important to have to same algorithm. If you have a conservative back-up (The Aeris is NOT conservative) you could find yourself in a position where the Aeris says your fine and the back-up says you've gone into Deco

You can see chamber tests here (from Scuba Diving magazine in 2008 when your XR2 was reviewed) You can see that the Mares is notably more conservative than the Aeris, based on these tests, the Mares looks to be just about a conservative as you get:

http://www.scubadiving.com/files/old/images/pdf/200806_chambertest.pdf

You can see the difference between new and old at Leisure Pro. If you really only want the Manta for a back-up then going with the old version and getting a nice discount may be the way to go.

Not that it in any way matters but If it were me, I'd get the new one and relegate the XR2 to back-up duty

new

old (it is even labeled as such in the product name)

 

[PiranhaChris]

The Cressi Edy is a good back up. the Edy 2 is my back up for my Cobra 1. and the Edy 3 will be out soon and it has a Nice Titanium Bezel
But the Edy 2 is great and is pretty much giving me the same readings as my Cobra (less the Air lol)

 

[jhelmuth]

I'm going to dissagree (to an extent)...

It's not necessary to have the same algorithm (primary and backup) - however, that does assume [A] you do not dive the extremes of your primary (IE - you stay at depth for every min. your computer tells you it's safe without going into deco [ and hopefully you'd never exceed that even]) and you ALWAYS include a safety stop @ 15-20 fsw for 3-5 mins (you DO do your safety stops - right?).

Certainly having a less conservative backup would NOT be a problem, but it IS correct that having a more conservative backup would POTENTIALLY create a situation where a deco obligation might have happened and - if brought out of the water without "clearing" - would lock-out for at least 24-48 hours (and thereby render it useless for all intents and purposes while on your trip).

Keep in mind, this is actually more rare than you might guess (but it can and does happen). The graphs and reference that CT Sean is showing you illuminates the differences in level of conservatism - but in each case it ultimately means that those are the limits on those dives. So - like I said - IF you push your limits, then you should consider only algorithms which are identical (or near identical). But if you are a typical recreational dive who practices safe diving, I don't see it being a problem.

PS - I do like what CT Sean pickkedd out for you...

All the best,

jim

 

[jhelmuth]

The Cressi Edy is a good back up. the Edy 2 is my back up for my Cobra 1. and the Edy 3 will be out soon and it has a Nice Titanium Bezel
But the Edy 2 is great and is pretty much giving me the same readings as my Cobra (less the Air lol)

...also a good choice!

 

[Crush]

My personal, totally unprofessional, opinion is that it's rather important to have to same algorithm. If you have a conservative back-up (The Aeris is NOT conservative) you could find yourself in a position where the Aeris says your fine and the back-up says you've gone into Deco

+1. If your backup goes into deco and it doesn't clear during your ascent and you ignore it (dive your main computer and ignore the backup's deco stops) then most computers will lock you out for 24 hours - you will end up diving with no backup.

I dive two computers and don't understand why others don't do this as well.

 

[jhelmuth]

Here's and even better possibility...

Change you computer batteries before you leave on your trip and/or have the computer checked out. Now you really don't NEED a "backup"...

Computers are really quite reliable these days (statistically I'd venture a guess of less than .5 % failur rate durring use when battery life is NOT a factor). Check you model out (some google searching ought to work) on frequency and type of "failures" which have been reported. You may be pleaseantly surprised.

Worst case instance is that IF your all's computers fail, you dive gauges and tables for the remainder of your trip (not really a big deal actually)...


Jim

 

[jhelmuth]

+1. If your backup goes into deco and it doesn't clear during your ascent and you ignore it (dive your main computer and ignore the backup's deco stops) then most computers will lock you out for 24 hours - you will end up diving with no backup.

I dive two computers and don't understand why others don't do this as well.

True... but you'd have to really be into some deco on the primary for that to happen (and/or blow off your safety stop)...

I've tried this out using ScubaPro/Uwatec vs Sunto vs Cressi vs Sherwood/Genesis vs Mares.... I've never been able to cause any of them to lock-out from a blown deco stop (again... diving within limits and practicing safety stops on all dives).


Jim

 

[jhelmuth]

+1. ...
I dive two computers and don't understand why others don't do this as well.

...because it's really not necessary and holds very little benefit.

 

[jhelmuth]

...and you could always just "rent" backups at the dive op where you travel to.