John Bantin has been a full-time professional diving writer and underwater photographer since 1990. He makes around 300 dives each year testing diving equipment.
COMPUTER MARA ASCENT-RATE ALARM
IT MAY HAVE BEEN A VERY LONG TIME AGO, but it sticks in my mind. I had just completed a BSAC Advanced Instructor examination, and the chief examiner honoured me with the invitation to go on a dive with him. Each of us was equipped with a Decobrain, one of the earliest models of diving computer available. When the time came to ascend, he signalled up and, before I could respond, he was gone. I looked up and saw him at the surface. When I finally joined him, I asked whether the little fast-ascent warning light had shown up on his computer. He denied it, and I reflected that if he always did his ascents in that manner, the little bulb of the indicator had probably blown long ago. So often I have heard about people getting bent while diving within the parameters of what their computer said was safe. I wonder if it has anything to do with a fast ascent. All the computers available today take into consideration an over-fast ascent, and penalise the diver with longer shallow stops to compensate. The problem arises when we are too busy to watch for the Fast Ascent-Rate icon on the computer display. Closely escorting students or looking through the eyepiece of a camera at some spectacular animal encountered in the shallow blue water, such as an oceanic whitetip shark, are instances that spring to mind. Diving in the dark can lead to some basic errors, too. Then it would be useful to have an easily understood audible warning, rather than the more discreet alerts given by your computer that could mean other things, such as that you are very low on gas (that's me at the end of every dive) or that your air-integrated transmitter has lost its signal.
YEARS AGO, I HAD A COMPUTER that relayed its information audibly while attached to a mask strap. It worked a treat, and continually updated vital data regarding depth and ascent-rate. In those days I shot a lot of old-fashioned video, and often had my eye glued to a camcorder eyepiece, so this computer proved invaluable. I wrote a glowing review of it, but nobody wanted to buy it, presumably because they would have been too embarrassed to wear it, so it disappeared from the marketplace. The Miniature Ascent-Rate Alarm, or MARA, goes a long way to doing the same job without replacing your existing diving computer, and would be very useful to someone who hasn't bought one yet and is relying on a depth gauge. Not only that, but it indicates a 5m safety stop.
This is all done by a series of squawks. The instructions describe them as rather more musical; 'do, ray, me...' etc. I found the squawks rather useful, in that they sounded more urgent as I broke the ascent-rate rules more determinedly and, once I reached the 5m mark, I certainly knew it was the place to make the safety-stop. Unfortunately, ascending in blue water as I was, without any datum, I really needed something that would tell me if I unknowingly sank deeper again. This the MARA does not do. This explains why my five-minute safety-stops, counted down on my computer and constantly restarted as I regained the 5m mark, always seemed to take more than 10 minutes! Whether you actually need a MARA or not depends very much on what you are normally doing during an ascent after a dive.