Destroy the Dive Table!

Abacus

OK, that’s just an inflammatory title designed to make you read this post but I’ve noticed a post doing the rounds on social media called ‘In Defence of Dive Tables’ . To be fair it’s an older article and it does raise a number of good and interesting points but it’s an area I feel quite strongly about too.

I make it a point of discussing dive tables with instructor candidates on IDCs as to how they feel about teaching them. The room is usually fairly split in terms of their perceived value. So here’s my take on them: Teaching dive tables to open water divers is a bit of a waste of time. And I’m afraid that’s not just my opinion. Given that PADI, whose background, don’t forget, is in educational systems, has deemed it unnecessary to teach them, then why bother? Although again, for fairness to the original article, it was before PADI revamped the open water course to make teaching computers mandatory and tables optional- before the update, you could choose which one you wanted to teach.

Let’s have a look at the arguments put forward in defence of dive tables and why I think it’s time to stop teaching them:

  1. Dive tables are universal.

I think that the point being made here is that if your computer gives up and you’ve been logging your dive depths and times then you can transfer that info to a table. You couldn’t for example dive with a Suunto and then switch over to a Scubapro for the next dive. If you’re worried about your computer crapping out then you can always carry a back up with you. But my main issue with this point is addressed in the next one

  1. Dive tables don’t crap out

No they don’t but they’re also pretty useless at backing up a dive computer. Because the table assumes a square profile (and don’t forget that even if they use an eRDP ml they don’t learn the multilevel function unless they do that option on their advanced course) as soon as longer, multiple or deeper dives come into the equation it’s not long before your computer is allowing you to do dives that the table says isn’t possible. Try going on a Red Sea liveaboard for a week and see if you can back up your dives on the RDP. You can’t.

Another really important thing to acknowledge is what’s actually happening in a real world context and the reality is that the majority of divers who learn to use tables never even look at them again. They head off on holiday and end up blindly following a dive guide around who is using a computer. That is fraught with even more potential danger as I’m sure we’ve all heard stories of dive guides who’ve forgotten to switch their computers from nitrox to air and end up taking everyone past an NDL. It makes much more sense to insist that the student diver use and understand a computer and therefore put the responsibility back into their hands. I often hear instructors say that people won’t buy a dive computer, but they don’t have to- most half decent resorts will have them available to hire so why not just treat it as an essential piece of kit from the offset?

Dive computers are very reliable these days but ultimately if you really want to back up one up the only way to do it is have a second computer and wear it on all the dives too.

  1. Dive tables prepare divers for more advanced planning

Well maybe… First off remember that none of the tables on the market are interchangeable and they all work in slightly different ways. Also you don’t need to go anywhere near a table to teach a nitrox course now and it’s all the better for it, for exactly the same reasons.

When it comes to tec, yes we use tables but they bear little relation to the RDP so I find it a bit of stretch to say that understanding how to use that table will help at a tec level. Especially when the RDP is all about staying within no stop times whereas dive table usage for tec is much more concerned with gas consumption and whether a particular profile is possible. Also bear in mind that after a bit of manual calculation early on, most tec agencies strongly recommend the use of desktop planning software to work out dives thereby reducing the risk of human error so we’re back at computers again.

There is a fair point here but it’s  bit like insisting that we should teach people to donate a 2m long hose in an out of gas emergency as that would prepare them for more advanced diving and that’s a whole different argument!

  1. Dive tables are good practice

For what exactly? Practising dive table usage makes you good at using a dive table. All the important parts of dive planning are covered by computers and are in the open water course. Let’s divide them out:

NDLs, ANDLs, Bottom time, safety stops, ascent rates and minimum surface intervals are all dealt with by a computer.

RNTs and Pressure groups are a quirk of table design that are an abstract way of working out repetitive dive times. They’re not required for dive planning if you’re using a computer.

Here’s the contentious bit: It’s your job as an instructor to teach this stuff without using a dive table as a crutch. The dive table gives you a structured way of covering this information but in an enormously heavy handed way which often takes up half an afternoon, sends the class to sleep and burdens them with lots of info they don’t need. It’s like insisting someone should learn to use an abacus before you let them on your laptop. I do understand that in some instances a table can be handy when someone is really struggling with some of the key concepts but in my experience this is rare.

Many instructors also don’t realise that they’re supposed to teach how to use a computer not just what a computer does. One example of this is that students are supposed to use the planning function on a computer to check their NDLs before a dive (On a Zoop, it’s easy, just press the button that says plan whilst in surface mode). This shows them how increasing depth decreases the NDL. After the dive they look again and then check again after a surface interval. This shows them how they have residual nitrogen and that it will be offgassing as they have their lunch. You need to talk them though how the safety stop works on their computer, how it tracks ascent times etc. You can use the PADI dive computer simulator in the classroom which, whilst not being the slickest program ever devised, still does a decent job of showing these things in action.

Personally I think that the time saved by not teaching tables let’s you get into much more detail on other important stuff like gas management, which is covered in more detail in the new open water course and doesn’t have anything to do with working out pressure groups. I’m intending to write a blog about that soon as it’s an important thing to make sure you cover.

As a final thought, it’s worth putting all of this into a bigger context: Is there any evidence to show that a lack of proper usage of dive tables or computers is causing lots of accidents? Not really, let’s be honest, the average NDLs and ascent rates combined with safety stops set by most tables and computers are very conservative and as long as divers stay within them they are very unlikely to come to harm. On the other hand poor gas management is definitely shown to be a cause of dive incidents. So my suggestion is that you move with the times, ditch the tables and embrace the chance to spend more time on more important things.

 

 

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