Computers versus Tables
Wow an interesting question and one that yields a number of important points…
[1] I’m of the school of thought that uses table creation software (eg ProPlanner from Delta-P) and then writes these tables onto slate and then dive that plan. I use all standard computers in gauge mode and I use a mixed gas computer as BACKUP. An odd arrangement – but think about it I know if the gas computer has failed or that something has gone badly wrong with planning as my tables should be the most conservative… If the computer shows loads more deco then THINK in water and work out why…
[2] I cut the following tables (a) DEPTH of Sea Bed + 2m, and a total bottom time of the PLANNED dive. (b) DEPTH of Se Bed + 2m and 10 mins to total bottom time for those dives you get to the bottom of the shot line and think where on earth is the wreck – or something is wrong and I’m aborting dive, and (c) DEPTH of Sea Bed + 2m, and a total bottom time of the PLANNED dive + 5 mins.
[3] The Technical dives you may have three gases such as AIR, Nitrox 32 and Nitrox 75% and these three gases are a reasonable combination for many dives that technical computers can handle.
[4] There is a growing trend for dives below 45msw to use normoxic trimix and as such you may have two or more gases for these dives. Personally I like doing 45msw+ dives on trimix as you are much clearer narcotically.
[5] I have seen many leading technical divers using two of the same computers and doing no dive planning using table generating software. Not sure I like the idea of this personally. I believe in diversity and I use a D-Timer (UUWATEC), Stinger (SUUNTO) and a full VR3 (Delta-P) as my devices on technical diving. I keep the Stinger in gauge mode for the trimix or multi-gas diving. Suunto do a range of new computers that are multi-gas and these are very good as your primary computer to use as a computer (non-gauge mode) until later with trimix and you can then use it in gauge mode. Others are emerging or have been around for a while now.
[6] Cut your tables onto a small 60mm by 30mm (wide) slate that you drill a hole top and bottom of this and enough bungie between these hols to go around your hand. On the top side put your main run time table and on the back your 5 mins longer at depth. In your pocket put the bug out 10 mins bottom and a copy of these two plans. This back of hand slate is very very effective and can easily be flipped over even with cold hands… Email me direct for a photo of this or post a reply and I’ll put a photo on my website.
[7] Don’t put too much reliance on these computers – please. They don’t know your Cardio-Vascular fitness, nor Hydration, nor other physiological aspects of your body. They are all based on a mathematical model (several different types which have though had a lot of dives done with them…) A computer will constantly calculate these theoretical tissue models for your given dive profile, but take care to add contingency for your deco as most models only just have you surfacing with tissue compartment(s) that have not long left 100% saturation. By diving to tables created by software like ProPlanner you will be building in a good amount of contingency given your profile will not exactly follow nor never exceed the chosen plan. Obviously you will follow your training for deviations from the plan – but you will dive conservatively to such a table plan.
[8] See my other post on Dive Computers as not all the algorithms are fully implemented in terms of each theoretical tissue compartment being fully calculated each time – some use look up tables or approximation tables.. so again take care on multi-day diving blindly following a computer. I’m not knocking the computers, virtually all I’ve seen over the last couple of decades have been really useful, accurate and good – but use them wisely as a tool. Batteries fail with low temp – often suddenly – don’t be in a situation that your screwed because you don’t have a solid plan for the dive and know what deco etc you have to do…
For more insight on this huge topic and for further information feel free to Contact Andrew.
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