The displays on my personal computer began to fade. Next, a code that I’d never seen before appeared, and then the digits all disappeared.
Back at the surface, I poured the seawater out of the battery chamber and cursed my stupidity.
Dive-computers are the hardest items of kit to test. Even the most basic offers a comprehensive range of functions, many customisable, that must be selected using sometimes complicated menus. They must be set correctly and also understood.
On that dive, I was wearing four computers. Three were test units and the fourth was my own, the one I know how to use and trust. I use it to ensure that I complete my dive safely, in case I’ve got a test computer that isn’t working (it’s happened) or I’ve misread a display (done that).
Or, perhaps, deliberately misprogrammed a mix, or caution zone, to put a computer into deco so that I can see those read-outs while still within the real no-stop times.
So, with my talisman out of action, I turned to one of the test units – the Suunto D5.
I reviewed the D5 in April after attending a pre-launch event at the NEMO tank in Brussels.
It was still a prototype. I dived twice, assessing displays including tricking the unit into thinking it was on a decompression dive and listening out for alarms while wearing a hood.
But there are problems reporting on a pre-production unit, and it wasn’t practical to test either its gas-integration features or, for obvious reasons, the built-in compass.
Moreover, the sophistication of dive-computers means that Mike and I have to pick and choose which features to write about and which to leave out, simply because of restrictions on space. This is understandable if you figure that the D5, for example, has a manual exceeding 60 pages and is an entry-level-to-advanced recreational model.
So, on a recent trip to Gibraltar hosted by Gibraltar SAC, I was able to take along a production D5 to test its capabilities in open water.
A problem with watch-style computers can be the small size of the read-outs. I’m in my 50s, and my eyes were never very good anyway.
As I’m often testing dive-masks, it’s usually impractical to use reading lenses. Once in a while, I’ve even resorted to a camera’s close-up lens to figure out my status.
The D5, however, has large digits that I could easily follow. It’s able to use bold displays by limiting the information shown digitally at any given time.
At NEMO, I hadn’t really set the computer myself, so it was good to see how straight-forward and intuitive the D5 was to use.
Three buttons let you enter menus, scroll up and down, select, set and exit. It’s slick and quick to do.
This is important, because you might need to make some adjustments fast as part of your kitting-up process, or based on your pre-dive briefing.
For example, if the D5 is being used in Gas Integration mode, you might want to change the pressure at which it alerts you to tell a divemaster that you’ve reached a certain stage, perhaps a turnround point, in the dive. To upgrade the D5 to gas-integrated, you add the Tank POD.
This radio transmitter, which relays tank pressure from your first stage to the D5, has to be “paired” to your computer, so that it doesn’t pick up data from another diver’s computer.
The Tank POD with the D5 showing the POD assigned.
With more sophisticated Suunto computers aimed at technical divers, one unit can be linked to multiple PODs to enable the user to make gas-switches to air, nitrox and heliox for closed- and open-circuit diving, and still have the computer calculate gas durations for each cylinder and adjust deco for the gas breathed.
With the D5, you’re restricted to air and enriched air, but you can still pair it to as many as three PODs to handle dive and deco mixes.
The POD fits to a first-stage hp outlet. Fitting a transmitter directly into a first stage can be difficult because of other nearby hoses getting in the way, or the way you orientate your reg, but Suunto includes a short hose to provide additional clearance if needed.
I had two regulators on test and was able to fit the POD directly into the hp port on each without a problem, so didn’t need the short hose.
For the D5 to calculate gas time remaining in minutes, you need to tell it the volume of your cylinder. You should also enter your estimated surface air-consumption rate – the default is 25 litres per minute. This could be a faff on a dive-boat when working against the clock to kit up, but is actually very quick and easy to do.
Similarly, you can quickly set your turnaround pressure or time, to alert you when you need to start heading back. It can also remind you to inform a divemaster when you’ve reached 100 bar, which is common practice.
A further alarm warns you when you hit the reserve pressure you’ve chosen, to help you avoid running out of gas altogether.
When equipped with the POD, the D5 continuously assesses tank-pressure drop, compares this to tank volume and estimates how long in minutes your gas supply will last. If your breathing rate alters, it quickly provides new estimates.
I very much like this feature for decompression dives, because it allows me to compare my total ascent time to my gas supply and ensure that gas-time remaining exceeds required stop-time. This allows me to plan deco on the fly.