In this age of technological innovation, where (if you have the dosh) you can have a computer built into a H.U.D. system in your mask, dive tables seem like a quaint and cumbersome anachronism of an earlier time in diving. As computers have evolved, it’s reached the point where even open-water classes are taught using dive computers. Truth be told, it’s not too surprising. Dive computers are generally much more reliable now than they were even ten years ago, and most new divers are more comfortable with electronic devices and interfaces than learning how to use dive tables. There are also arguments over which tables are best and considerable difference in ease of usage. Now, while I do use two computers for every dive (my trusty Suunto D4 and Oceanic B.U.D.), I always have my dive tables on the boat or on shore. This post is about why for the latter and my two cents on the former.
Dive tables are not all made the same, nor do they use the same algorithm or number of theoretical tissues. Bühlmann tables are very different from PADI’s DSAT, US Navy and DCIEM; and each of those sets of tables are different from the other three. By far, US Navy derivative tables are arguably the most widespread tables in use. SSI, TDI/SDI, NOAA and NAUI all use variants of US Navy tables. PADI tables are the most heavily used, by dint of the fact they are the largest diving organization in the world. Bühlmann tables are usually used for computers, but you can get physical tables if you wish. DCIEM are the least common in my experience, being limited to use by cold water navies (like Canada’s, for whom they were made) and commercial/scientific work in Canada.
Owing to all of the different variables used in all these tables, and how/who they were tested on, and what they were designed for, they all give different NDLs, RNTs, and repetitive dive limits. Some are easier than others to plan a multilevel with than others. With all of that said, my preferred tables are DCIEM for safety if I’m doing a lot of diving, and NOAA tables for their ease of use if I’m doing light diving. That said, DCIEM has better multilevel dive planning ability, and are the most thoroughly researched of the tables available for divers. I can hear it now though “But! But! US Navy! They have tonnes of money for research!”. The reason I say DCIEM is because they were designed and tested using a wider selection of age groups, fitness levels and both sexes during their research phases, and all in cold water. However, if I’m not doing a tonne of diving (or if it’s just recreational stuff), I use NOAA. I like the speed of use and ease of use of NOAA, and if it’s just a day or two of diving, NOAA will beat DCIEM in my books.
Now, some of you may be wondering why I’m talking tables when I clearly stated I dive with a primary and secondary computer. The answer is simple. By having my tables with me, I’m insulated against my own forgetfulness (I can’t be the only one who’s forgotten their computer on the way out the door), and have a backup system in place in case of computer failure. Computers are great, there’s no bones about it, but they can and do fail. Batteries can expire, they can randomly flood, sometimes they just don’t feel like working. Most of that can be avoided by regular maintenance by technicians, but regardless, it’s a risk. By having tables with your gear, should your computer fail, you can surface, check your max planned depth to max time (to be safe), then plan for more dives. Sure you’ll be a “square” diver, but at least you’ll be diving safely. REMEMBER: at no time is it ever safe, or appropriate to dive two to one computer. Computers follower a single diver’s decompression schedule based on their depth, as little as 1m difference can affect bottom time and decompression schedule.
So, that’s my take on dive tables. They’re a very useful redundant system, in case things go wrong; and while all dive tables have pros and cons, my preferred ones are DCIEM (especially if I’m doing fun dives between work ones) and NOAA (if it’s just fun or short term). It’s worth mentioning that a lot of computer and table problems can be solved by proper dive planning. Read about that here.
Until next week, good luck and good diving!