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Saturday 15 May 2021

Dive computer ascent rates

I have read a number of articles in regards to dive tables v dive computers and I am astounded to believe the vehement defense of dive tables. 


My first retort is the difficulty of dive table use for repetitive diving, the majority people can learn table use locking the procedures and terms into short-term memory but when tested three months later are unable to recall dive table use.

The ascent rates prescribed on the majority of dive tables are simply outdated, there is no defending an ascent rate that was a compromise in the 1950s and still used today.

Getting newly certified divers to follow an ascent rate without an ascent rate indicator is nearly impossible, getting back to a shot line isn't always practical and even then, the majority of divers still ascend way too fast on a line without dedicated training.

Training divers to follow the ascent rate of their computer has many benefits, from early on in their training, the instructor is able to reinforce ascent rates and safety stops. A number of dive computers now have safety stop timers so at least a three minute stop is incorporated into ascent procedures.

More modern algorithms utilising micro-bubble prevention strategies also incorporate deeper stops in direct contrast to neo-Haldanean models seeking the highest pressure gradients to reduce decompression obligations.

We seek technological advances to enhance our lives, we carry around more computing power in our pockets than the Apollo astronauts took to the moon. We need to teach divers how to use their dive computers, this is a great tool - use it.

Once upon a time, dive certification courses were around three months in duration and highly physical in nature. With better instructional techniques and learning materials, the process of instruction is enhanced.

I sometimes ask myself, do you need to know how an engine, transmission, drive-train, steering, brake and electrical systems operate to drive a motor vehicle or do you just need to know where to put the fuel and how to turn the key?

Does the average person understand electron theory to illuminate the room at night or do they just flick a switch? Do they require a working knowledge of refrigeration including the latent heat of vaporisation and thermal expansion valves to work the coolness switch on their fridge?

We no longer use J-valves, twin hose regulators or wear horse collar buoyancy devices in diving just like you no longer need a motor vehicle to mount a mobile phone; this is outdated technology that should be relegated to museums.

When was the last time anyone actually used an abacus just in case a battery failed in a calculator? I also laugh when people say what if a computer fails underwater? Dive computers fail, this is a fact of diving and divers should be prepared for this inevitability.

Then you follow the profile of the person or team you are diving with, then the response always is, but they could be following a different profile with depths and times - this doesn't happen on tables? Plenty of areas around the world only allow guided dives, the divers follow the dive guide around and they plan the dive profile.

If that is the case, then I would be asking more serious questions about in-water diving habits and less about dive computer use. This is why dive guides are employed, this is exactly their role, they plan and supervise diving activities.

I now advise new divers to consider their dive computer as their first item of equipment purchased. The prevailing wisdom is to purchase the mask, snorkel, booties and fins kit; yes, these are important but the most relevant dive planning and execution tool.

Many would argue you can dive without a computer but you can't dive without a mask, fins and other equipment - fair comment. Sure, people dived for decades without dive computers, I began diving on tables and used the PADI Wheel for multi-level dives.

If you follow your dive computer recommendations maintaining a slow ascent rate then you will reduce the incidences of micro-bubbles in your tissues and more than likely decompression sickness. Oh yeah, you can also maximize your bottom time and execute multi-level dive profiles - a great tool.

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