The Essential Backup Computer: Part 1

These days, a preponderance of divers recognize that having a backup computer is essential to continue your dive safely. If your primary were to fail, that second computer would let you get back into the water and continue with follow-up dives.

Undercurrent recently asked readers for details about their diving with backup computers, and we were inundated with interesting replies, many of which were quite telling.

Dive trips are awfully expensive these days. Each dive has a value that cannot be replaced if you need to sit out for 24 hours and subsequently lose three or four dives because your computer went into SOS mode, blocking you from further use.

Sometimes, this means a diver used his computer incorrectly, inadvertently or intentionally, and missed mandated deco stops, jeopardizing his health. Other times, it means the computer malfunctioned. As Laurel Fulton (Denver, CO) asks, "How many of you have been on liveaboards where someone had their main computer crap?" It happens more frequently than we'd like to believe.

Redundancy Does Rule

We've known divers who pay a hefty price to journey halfway around the world to dive but don't want to spring for a backup computer. Of course, that's ridiculous. As Mary McCombie (New Haven, CT) points out, "The price of a backup computer equals the cost of one day of liveaboard diving - cheap insurance in my book."

Not one to mince words, Ken Kurtis (Los Angeles, CA) says, "I carry a backup because I have an aversion to lying on my back for six hours in a chamber because I was too cheap to spend a couple of hundred bucks on an additional safety measure."

David Bader (Norwood, NC) said, "I follow the same philosophy with computers as I do with dive lights. Two is one, and one is none. A dive computer failure will end a dive quickly if you dive with only one computer."

And never expect to get your computer repaired when you're on the road. Fredda Lerner (Annandale, VA), whose old Suunto Favor flooded, found she couldn't get it fixed in Bonaire. "I learned the hard way why a second computer is so important."

Why Computers Fail

A common reason a computer fails is that it floods. Typically, when the battery was replaced, the compartment wasn't properly sealed. There's no excuse for that when it's done professionally because the computer should have been pressure tested. When divers change their own computer batteries, most don't pressure test, so the chance for failure is greater.

Also, some computers fail electronically: an error in manufacturing or mistreating the computers are two reasons. An internal electronic failure or a flood can be disastrous.

Here are a few tales of woe from our readers:

Larry Stewart (Knoxville, TN) was diving in Bonaire in 2017 with an Atomic Cobalt 2 "when it recorded no dive profile at first, then displayed a dive for 1093 minutes at a depth of 3551 feet."

Now, that's a failure of electronics! His wife dives with the same computer, and hers stopped reading tank pressure a couple of years later. You can be sure both went back to Atomic Aquatics for repair.

Jim Fox (Bellevue, WA) used to carry the Atomic Aquatics Cobalt and says, "My spouse had computer flooding twice, and an electronics/sensor/software failure, and I had an internal O-ring failure on the connector. The magnetic switches failed early and often due to corrosion of the magnets that were embedded in the controlling touch-pad."

Vick Thomas told us that he and others had encountered problems with their rechargeable Cobalt 2 computers that were unable to retain a charge and believed that "a batch must have had defective batteries." He later had problems with the buttons becoming inoperable. The Cobalt 2 is no longer produced though you can still spot divers using them.

Carol Cohn (Livermore, CA) wrote, "I had several Liquivison X1s and an XEO, all of which had screen failures while diving. Since I was also diving with a Suunto Vytec, I had no issues."

Since the mid-'80s, Larry Molnar (Cleveland, OH) has had three fail during dives. "One failed due to low battery power, although there was no warning (Scubapro DC-11). My Scubapro Chromis failed on its third dive due to a chip error, and my Cochran Commander failed due to a software glitch. I once flooded an Oceanic Atom due to my error in resealing the back."

Dean Christofolis (Colorado Springs, CO) recently purchased an Aqualung i330r, and on a liveaboard trip to Belize, "had several issues including the program not properly providing credit for surface time for O2". After a couple of days of diving, it locked-out for 24 hours. My backup worked fine, and I finished the week using it."

Those are just a few examples of divers who wrote us about their computer failures, giving plenty of reasons for carrying a backup.

A Bit of Prevention

Of course, you must service your computers.

Jim Reilly (Lafayette Hill, PA) gives sage advice when he says, "We have all of our equipment serviced annually and are fussy about who does the servicing. We always do a few shallow dives first to ensure all is well with our equipment before doing more challenging dives."

Bill Harward (Portland OR), who has more than 1100 dives, says he dives with two and tests both at least twice before diving and verifies his batteries are charged. To date, he hasn't had any of three different Suunto computers fail.

Some trust their old computers so much that they have them rebuilt, even if they have failed. A long-time Undercurrent subscriber from Ohio has rebuilt his "first-generation Oceanic integrated nitrox computer several times." False economy, we say. The low cost of electronics and the more advanced computer algorithms make new models better and safer. That ancient Oceanic runs on a decades-old DSAT algorithm that has been called into question by serious divers, causing Oceanic to introduce the Pelagic Z+ alternative in its later dual-algorithm products. That Oceanic is the equivalent of a cathode ray tube television in a flat-screen world.

What Makes A True Backup Computer?

Astute divers carry a backup computer on every dive to track their decompression status parallel with their primary computer. So, we were amazed at the respondents who kept their backup computers in their dive bags. That qualifies as a replacement computer, not a backup.

An experienced California diver told us, "I carry two computers onto the boat but dive with just one, a Shearwater (the standard); the backup is an older Suunto. I do not want different algorithms underwater, so I leave the Suunto on board in case of trouble with the Shearwater." But, if the trouble comes underwater, he's got no accurate way to guide him to the surface, and if his dive operator is enforcing it, no way to avoid the 24-hour no-diving rule. A backup Shearwater will solve his dual algorithm issues.

A diver from Vienna, VA, falls into the same trap. He wrote, "One goes on my gauge console and the backup in my dive bag." He also said, "I like that you don't have to turn it on or off - just jump in the water, and it turns on by itself." These days, all modern dive computers do that.

Safe diving is about redundancy: carrying duplicate equipment that can seamlessly replace any piece that fails during the dive. For example, Giampaolo (Plymouth, MN) told Undercurrent that he carries two Mares computers (one on each wrist) just as he carries a spare mask. "I never had a problem with a diving computer during a dive, but that doesn't deter me from being prepared if it happens. I would not want to abort a dive or rely on someone else's computer."

And there are a few divers, a dying breed, who like to streamline themselves so much that they dive with the fewest gadgets they can. To them, a second computer is one more thing to get in their way. To these folks, we say, "just put it in your BC pocket." It doesn't matter where you carry it as long as you can get to it easily. You might wear it on one wrist, even alongside your primary. Or mount in a console or on a high-pressure hose. But it's not a gadget to avoid because it's just "one more thing to get in your way."

Craig Capehart (Carmel, IN) says he wears "a dive computer on my wrist and another attached to my BC near my right shoulder. And I keep a spare in my room. Despite technical failures being rare, there is operator [my] failure on occasion when, after an excessively long surface interval, Nitrox settings might revert to air, and I don't notice it."

So, while the case for the backup computer is clear - for most divers it's been clear from the outset - there's more to say in the next issue.

- John Bantin