A dive computer allows divers to extend their time and safety while in the water. Considered by many as an essential item (and in some dive resorts around the world they are mandatory).
Read down for more information or go straight to the Dive Computers department.
Since back in the 80's dive computers have been revolutionising the way that we dive. Before the dive computer came along you would calculate your dive time based on the maximum depth you were diving to.
The dive computer changed this significantly by being able to calculate your max dive time based on the actual dive allowing Multilevel diving. Modern dive computers update you constantly on how much time you have left, based on your current depth.
Essentially this allows you to remain underwater for longer in safety with potentially shorter safety stops.
Computer Aided Diving
A dive computer should not replace your dive tables but should be used in conjuction with your tables.
Dive computers today are incredibly reliable but like any computer, they can go wrong and without a good idea of what should be displaying how will you know?
For example you should know that if the maximum dive depth is 30m, when you get there your dive computer should be showing around 20 minutes and that if it shows 60 minutes there must be something wrong. This is the difference between computer aided diving and computer dependent diving.
The only practical back up to a dive computer is PADI RDP Wheel which can allow you to plan multi level dives and all divers should consider buying and learning how to use one - this is covered in the PADI multi level diver course.
The course also includes tuition on how to use dive computers too and is highly recommended.
Air or Nitrox?
When purchasing a dive computer your first choice is to decide whether now or in the future you will want to dive on nitrox (Enriched Air)?
If there is even the slightest chance you will, then you should only consider computers which have nitrox diving facility to save money in the future.
The difference in price is only slight and most manufacturers are now starting to produce all computers with nitrox diving capabilities.
Remember if a dive computer can calculate nitrox then they can also calculate air diving (to the computer, air is considered nitrox 21).
Nitrox diving should only be performed however, once you have completed the PADI enrichred air diver course or similar.
You may want to consider not only logging your dives in your log book but also on your PC.
All major manufacturers now have models that can download your dive data to your PC.
This allows you to see your whole dives in profile and provides extra information not noramally accesible via the dive computer itself.
Some computers are now including the download software whilst with others you have to purchase them seperately. Amazingly (and infuriatingly!) some interfaces still have the old fasioned serial connector for which you may need to purchase seperate a serial to USB connector.
How Dive Computers Work
Decompression sickness is still not completely understood and it must be remembered that a dive computer will not make you immune to decompression illnesses.
The saying "if you want guarantees, buy a washing machine" possibly sums up the general consensus. However dive computers do improve your likeliness of having a safe dive.
They work on a mathematical algorithm (such as the Suunto RGBM) which classifies tissues within your body into similar compartments within the algorithm - some as fast tissues (such as brain and heart which have a lot of blood flow) and others as slow (such as bones which have relatively little blood flow).
It then takes time submerged and your depth and calculates how long you can safely remain underwater. This is a very simplistic explanation of a very complex calculation and more detail is covered in the PADI divemaster course or there are many books on the subject if you wish to learn more.
With an air integrated dive computer you have another great benefit in that the computer can also calculate your breathing rate, telling you how much time you have left to dive at your current air consumption.
This facility also allows the computer to monitor and learn your breathing rates so that if the current is behind you and your breathing slows, the computer can rightly calculate that you absorb less nitrogen and therefore you can remain underwater longer.
Air integrated dive computers can either be hosed or hoseless (via a transmitter on the first stage).
Wrist Or Console Mounted?
The fashion in the UK is for wrist mounted computers whereas in most other areas console mounted computers are the norm. There are arguements for both systems but here are a couple of points you should consider before deciding which would suit you best:
Console mounted computers are larger and are attached to your equipment via a hose. This makes them less likely to be mislaid.
Console mounted computers use battery power even if only training in the pool meaning the more you practice, the more you will spend on batteries.
A console mounted dive computer is not necessarily an air integrated dive computer. The pressure gauge in your console requires a connection to your tank in order to show a pressure reading, but this does not mean that the computer is connected to the air source too.
Wrist mounted computers can be used for other purposes such as freediving, they can also be used from day to day depending on the model
Most dive computers will have visual and audible alarms to warn you when you get close to a limit, such as no stop time approaching, fast ascent etc.
These are very useful especially for new divers to remind them to look at their computer! You should read your manual to ensure you understand what the alarms mean.
There are a few basic considerations with using a dive computer which you should be aware of:
Read the instruction manual throughly before using the computer.
Never share a dive computer; if one of the buddy pair is not diving on a computer you must abide by your dive tables.
Do not "ride the zero", this is waiting for the no stop time on your dive computer and then ascending a few metres and waiting again to stay underwater longer. Although a dive computer is meant to extend your dive time this is pushing your luck.
Remember, to help avoid decompression illnesses follow the common sense suggestions you learned in training, avoid dehydration, alcohol etc.
Modern dive computers are generally made with user changeable batteries. However only a few have watertight battery chambers meaning that if you fit the battery wrongly and it floods, the whole computer is ruined.
For this reason most divers still return their computers to service centres such as ours for battery changes and servicing. Although more expensive than doing it yourself, having professionals do it is much less expensive than a new dive computer.
Screen guards are now fitted on most dive computers to stop the screen getting scratched.
These guards will quickly become very scratched and although difficult to read on dry land once submerged the scratches virtually disappear. However if the guard becomes too scratched or cracked replacements are available.
If your computer does not have a screen guard make sure you purchase a perspex (not stick on) cover for it.
Suunto RGBM - Reduced Gradient Bubble Model
The Suunto Reduced Gradient Bubble Model is a state of the art algorithm for managing both dissolved gas and free-gas in all its stages in the tissues and blood of the diver.
It is a significant advance on the classical Haldane models, which do not predict free-gas (microbubbles). The advantage of Suunto RGBM is a more accurate representation of what is happening in the diver's body, through its ability to adapt to a wide variety of situations.
The Suunto RGBM addresses a number of diving circumstances that have not been considered by previous dissolved gas models, adapting to:
Continuous multiday diving
Closely spaced repetitive dives
Dives deeper than the previous dive
Rapid ascents which produce high microbubble build up
The Suunto RGBM algorithm automatically adapts its predictions of both the effects of microbubble build up and adverse dive profiles in the current dive series. It will further modify these calculations according to the personal adjustment that a diver can select.
Essentially when you dive you take on gas, this is called on-gasing. You need to off-gas for a sufficient time during surface intervals to avoid illness, the Suunto RGBM helps you to do this correctly.
There is currently only one mask mounted computer available, however now the trend has started its sure to continue.
Mask mounted computers have the advantage that you can keep an eye on your dive computer without any movement, this can be an advantage for techincal divers or photographers who need to stay motionless.
They work by having the screen for the computer mounted inside the mask.