backup computer

[Cthippo]

I dive solo on a single computer, but these are fairly shallow NDL dives where the consequences of a computer failure, either pre-dive or in the water, are tolerable. If I was doing deco diving or even multiple dives a day where I am counting on it to do something critical for me, then I would want two computers as identical as possible.

 

[happy-diver]

Ok on a trip, but Shirley even from deco you can get to the surface without one and internet yourselves another

 

[chrisch]

There is an argument to be made for running two computers to overcome failure of one and use the working one for repeat dives. A liveaboard holiday for example. For day to day diving less so, maybe a spare in your kit bag for when you forgot to change the battery in the main one. (My option)

A single computer is just fine most of the time and if you have a computer failure you can the dive and head up. Any deco - just follow the buddy diver's profile and add a good safety margin. Solo? Use gas consumption to guide you for your stop and dSMB for depth - personally I wouldn't run into any deco when solo anyway, that is a step too far.

My spare is a 20 or more year old Oceanic datamax. New battery (user changable) now and then and it works fine.

 

[Centrals]

The back up must be more liberal than the primary.

 

[Capt Jim Wyatt]

Two Shearwater computers whether solo or not.

 

[DiveLikeAMuppet]

1 Shearwater tracking actual deco
1 backup set up as a bottom timer (cheapest Suunto)
Deco plan written down in wetnotes (how the plan looks like depends on agency and training)

Works well for square-ish profiles, forces you to plan your dives as a bonus.

(And if you end up with a CCR, your main Shearwater will become your backup …)

 

[gamon]

The back up must be more liberal than the primary.

Well no, in fact it doesn't. If you're diving so close to the ndl limits that one of your two (or more) computers puts you in deco you have the option to either ignore it and let it lock you out, or follow the more conservative computer.

I know what I'd do.

 

[Centrals]

Well no, in fact it doesn't. If you're diving so close to the ndl limits that one of your two (or more) computers puts you in DECO you have the option to either ignore it and let it lock you out, or follow the more conservative computer.

I know what I'd do.

I also know which one I will follow, definitely not the liberal one.

 

[gamon]

I also know which one I will follow, definitely not the liberal one.

In my experience when diving with 2 or more computers which give different results, the most conservative computer, when in deco, clears upon ascent without a need for a stop.

 

[ToneNQ]

Ideally you want two computers running the same algorithm, and the same gradient factors if the computer is fancy enough. But this depends on the type of diving you're doing. If you're solo diving inside NDLs, all you need are two computers basically acting as a depth gauge and a bottom timer. A Suunto and an Oceanic computer would give you different NDL times at depths if you push them, and a Suunto will lock you out for 48hrs if you ignore a safety stop.

You could easily use a first computer like a cheap Oceanic Geo, then move to a Peregrine or a Tern as the primary for basic Tech diving. If you're serious about technical diving, be aware some computers limit the amount of different gas mixes you can run, or those that default gradient factors. These may never hinder you, just make an informed decision. Shearwater are not the only option and you can be safe with others, but there is the reason the Petrel and Perdix are the dominant computers in technical diving.

I have carried my old computer (Aqualung i300) as a backup in the past but as I've tried to streamline my gear I have ditched it for recreational diving. Instead I still keep a console with SPG and depth and in the event of computer failure so I can still manage to abort the dive safely and make a 15-20 foot deco stop.

Query to the group whether ditching the console in favor of a lollipop SPG and backup computer is the right way to go?

Standard technical gear is a back-mounted twinset with an SPG off the left post, clipped off on your left hip and a backup computer on the opposite arm to your primary. Sidemount will have lollipop gauges on each tank. Many tech divers use air integration and carry no SPGs.

There are few hard and fast rules for the bulk of the training agencies on how you configure your gear, your solo/tech instructor will guide you on their thoughts. After the course you can apply that to your own risk appetite and budget and vary your approach as you need to.