Thailand – Australia – United Kingdom

Archive for December 19, 2009

Shearwater Research Pursuit technical computer

It is available in five configurations to suit your diving from the basic air/nitrox scuba version to the fully loaded nitrox, trimix and heliox open and closed circuit model with external active one and three cell ports. Each configuration is fully upgradeable to any other via a personal code, so you can upgrade as your diving progresses.

It uses a Buhlmann algorithm to calculate its decompression obligation, but you can adjust the algorithm across a variety of settings if you want to dive more conservatively than the default. Interestingly, if you miss a stop it doesn’t lock but carries on in a ‘best guess’ mode – especially useful when incidents occur. For calibration at the surface in closed-circuit mode there is a user-selectable oxygen percentage although most divers will probably choose to use pure oxygen. As with the majority of computers on the market it is automatically switched on by depth and/or pressure, and features an automatic, ambient light-sensing LCD for back-light illumination.

It is configurable for either automatic or manual set point changeovers with both set point and sensors being displayed while in the menus. The decompression algorithm uses the current PPO2 (partial pressure of oxygen) as a FiO2 (fraction of inspired oxygen) and will thus on-the-fly predict TTS (time to surface) and length of stop time.

Gases can be switched during a dive and there is a preset selection of gases that can be inputed – like setting favourite stations on a radio. As well as the obvious basic diving information, other useful displays include, ascent rate, milli-voltage readouts for all cells on demand, battery voltage, low battery warning and CNS tracking. The battery can be changed by the user and has a life expectancy of 360 hours.

Getting to grips with the Pursuit is straightforward. Disappointingly it only uses two buttons so there is a certain amount scrolling to be done. An open circuit comparison of the Pursuit’s algorithm in both air and nitrox mode over several dives showed that it was less conservative than the algorithms of both Suunto Vytec (set at one minute deep stop) and the VR3 by up to several minutes on longer and deeper dives – all computers were at factory default settings.

We tested the Pursuit on an open circuit dive using a 17/30 back gas, with 30 per cent travel and 80 per cent deco mixes to a dive to 64m for a bottom time of 20 minutes and found it cleared nine minutes before the Suunto Hel02.

John Adams commented, ‘I used the Pursuit and set it up to match the settings on my Vision electronics. It was used as a standalone computer (not plugged into any other cells) and in CCR mode. The Inspiration was set up with a diluent of 10/53 and gradient factors of 15/85. The gases in the bailout cylinders were 18/45 and 65 per cent nitrox. Setting up the Pursuit, once the correct system of tapping the contacts had been established, seemed logical and easy. I found it much easier to program than the VR3 and managed to do it without consulting the manual. This is an important point as I believe many UK divers would do the same. With the same gradient settings, I found the deco information matched fairly closely to that of the Vision and it was very easy and clear to read. Although I do personally prefer the slowly rising ceiling of the Vision, I wish their display had the lighting features and print size of the Pursuit. As I get older and my reading prescription changes – there must come a point where it is cheaper to buy the Pursuit than keep buying new prescription masks.’

For CCR users, Narked at 90 also provides various cell kits that can be directly linked to the Pursuit. One unit that may be of particular interest in the UK is the three-cell monitoring back-up kit (£267.06) that is specifically designed for the APD (Ambient Pressure Diving) Classic Inspiration and features what Narked at 90 claim to be the only detachable cell holder in the world. As a good demonstration of how closely the Pursuit matches the APD calculations see the picture of it in action (left). The photograph was taken during a dive where the maximum depth was 51.9m with just under an hour on the wreck. The Pursuit shows 10 minutes TTS and the Vision shows 12 minutes, which is pretty close after 90 minutes of elapsed dive time.

The Pursuit has user updateable firmware via an infrared interface and free software updates are provided for life. At well over the wrong side of a grand the Pursuit is not cheap but on par with other similar featured computers in the market.

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