Home Innovations Shearwater GF and VR3 - Technical dive computers

Shearwater GF and VR3 - Technical dive computers

Technical diving is an extreme sport within the diving world, and like any other activity, the people who push their sport to the limit demand better and better equipment, which can deal with their exacting demands.

While diving computers have progressed rapidly over the years from the most basic lump of metal that gives depth and time, to the modern watch-style fashion jewellery with multiple nitrox mixes and all sorts of extra functions, the technical diver wants even more from their unit.

These divers want all the advantages of computer diving while still being able to use several different gas mixes containing multiple gases, and even offering the ability to connect to a rebreather unit and analyse the gas they are breathing. Obviously the choices at this level of diving become slightly more limited, but two of the computers on the market which can offer the technical diver almost everything they require are the VR3 computer from Delta P Technologies in the UK and the Shearwater GF computer from Shearwater Research Industries based in Canada.

The VR3 is often advertised as the only dive computer you will ever need due to the fact that it is user-upgradeable through a series of unique PIN numbers which can be purchased at any time after getting the computer.  This means that which ever level of diver you are, you can buy the computer to suit your needs knowing that if you ever progress in your diving at a later date, you don’t need to replace the computer, but simply purchase the upgrade to the level you require.

The diver can program in up to ten different gas mixes containing any mixture of oxygen, nitrogen and helium and access these gases at anytime; including changing the contents of the mixture under the water should you need to. The VR3 also has a closed circuit rebreather option, allowing it to become a fixed partial pressure computer, either on it’s own, or even wired into the rebreather unit, to give a real-time reading of the gas within the rebreather and consequently compute all the gas loading calculations based on what the diver is actually breathing at the time. Because of its gas analysing capabilities, the VR3 can also become a stand-alone nitrox analyser to check your gases before you even dive!

Under the water, the screen is fairly easy to read and understand what information is being displayed, although obviously with so much more information being displayed, the diver will have to get used to the computer before using it on complicated dives.  The same goes for the menu options and navigating the computer’s various functions.  The VR3 can do so much both above and below the water and has so many user definable settings that the menu options do seem to go on for ever, so time must be taken by the diver to get used to the unit and find their way around.  With practice it does become very easy to know which of the VR3’s two buttons to press and whether to do a long or short push and so access can be gained easily to any function over time.

The new version of the VR3 has the option of a colour screen and a high pressure interface to give tank pressure readings on the screen.  The decompression model used by the computer is the Buhlmann ZHL16 model which incorporates two minute ‘deep’ stops or micro bubble stops throughout the deeper portion of the ascent before reaching the ‘proper’ decompression stops.  The stops are easy to follow with the depth and time of each being displayed, but also with a unique ‘diver on the line’ graphic, which allows the diver to slowly ascend throughout the stops to allow a more gradual decompression schedule rather than jumping from stop to stop.

The VR3 takes a user-replaceable AA size battery, either conventional 1.5V or a lithium 3.6v version, and the logbook can be downloaded into a PC via an infrared link and the accompanying software.  The VR3 is a solid computer and can deal with the needs of any technical diver, whatever their requirements.

The Shearwater is an open and closed circuit air, nitrox and trimix decompression computer, which also has the option of being connected directly into a closed circuit rebreather.
Unlike the VR3, the Shearwater takes a reading from all three oxygen sensors in the rebreather unit individually. Then uses voting logic as an average to accurately calculate the divers inert gas loadings and hence the no decompression time or the decompression schedule to be completed.

The Shearwater can be programmed with up to five open circuit and five closed circuit gases. Through a very user-friendly menu system and they can easily be switched between or changed under the water should the diver carry out gas switches, or need to change from closed to open circuit during a dive.

The decompression model used is again based on the Buhlmann ZHL-16C algorithm but with added gradient factor conservatism, with a number of pre-programmed levels of conservatism available to the diver depending on the diving they are conducting.  A number of divers prefer this decompression model over the older Buhlmann models and are switching to this more graduated continual ascent without deep stops, considering it to be safer on certain deep dives.

The screen is very large and the display extremely easy to read and understand, making diving with the unit very stress-free without the need to spend ages studying all the numbers. Again, the logbook can be downloaded to a PC via an infrared link so the diver can see all manner of information displayed for later reference. Two buttons control all the menus and selections making navigating the various options a very simple affair.  Although slightly larger than the VR3 computer, the Shearwater is nevertheless a very compact unit considering the amount of functions it contains.

Whilst diving, the Shearwater displays the gas mix, total time to surface, depth, time, decompression stop depth and time required at the stop depth.  Should it be used with a rebreather then it will also give a continuous readout of the three oxygen sensors as either a partial pressure or millivoltage reading.  It was extremely easy to use under the water and the decompression model gave a very nice ascent profile and actually reduced the total ascent and stop time when compared to the profile given by the VR3.  This just goes to show that it’s not necessarily the length, but the quality of decompression, which makes the difference on technical dives.
I use both these computers side by side on every dive with the VR3 being a backup to the Shearwater which I have connected into my rebreather. I am very happy with both units on all manner of dives from shallow no-decompression dives right through to trimix dives below 100 metres.

The only real down side to both computers compared to most other dive computers on the market is the price, but obviously the more functions a computer has, and the more the diver expects from it, the higher the price goes.  The VR3 is more expensive if you choose the fully upgraded version at around $1800, with the Shearwater being $1300 for the stand-alone computer without rebreather connection; otherwise it’s $1600 for the complete package.  Needless to say, in the world of extreme sports, the cost of equipment increases the further you want to push the limits and diving is no exception to this.  Ask any technical diver!


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