Dive Computer Algorithms

Dive Computer Safety

Any of the diving computer's that you can buy today at Mike's Dive Store will do their equal best to stop you getting damaged by decompression illness, provided you understand and follow the guidance they give. However, years ago it wasn't necessarily so. Some of them used philosophies that varied widely from the mainstream. I use the term 'philosophy' because it's all based on theory and every person is different so no diving computer manufacturer can guarantee that you won't get a bend. That said, considering the numbers of dives safely done world-wide each year, you've got to be very unlucky indeed.

Most diving computers allow you to add degrees of caution. You may be over-weight or over-age. You may have some health issues. None of these necessarily stop you diving but you should take them into consideration when setting up your computer before diving.

There used to be an Italian brand of computer that advertised the fact that it gave you more bottom time than others. This equated to less safety. Is that what you really want? Thankfully it soon disappeared from the market place.

More insidiously, a very popular brand of computer used to use an algorithm or mathematical model that was intended for no-deco-stop diving to depths less than 30m. That was fine as long as the user was aware of that but of course, often they were not. It gave lots of no-stop time up until the moment that the remaining no-stop time ran out, when it switched to a different table that often then required extensive time at shallow depths before the user could be assured that it was safe to surface. Of course, this usually happened towards the end of a dive at a time when the diver was getting low on air. We saw lots of these computers tied off and dangling beneath boats at around 6m deep while the owner climbed out and went for lunch - albeit feeling a little insecure.

You can still buy computers with this algorithm and provided you intend to use it to manage no-stop times and never go beyond that, they'll probably be fine. However, these same computers now have dual algorithms installed and you can opt for the one that ties in with other mainstream computers. 

The fly in the ointment is that few of us bother to read the complex instruction manuals that usually come with computers so I've often witnessed divers doing complex leisure dives unknowingly with an inappropriate algorithm.

I was in Truk Lagoon when my buddy, so equipped found he had 25 minutes more no-stop time while I was decompressing on the trapeze hung under out boat. He continued to dive at around 20m deep and didn't get bent but we have no way of knowing how close to the edge he came.

A lady diving alongside me queried the fact that her two computers of different makes gave widely varying information. I simply later set the offending one to the algorithm that matched the other and she spent the rest of the week much happier.

If you buy a computer fitted with such a dual algorithm, be sure ask the person that sells it to you to set it to the algorithm appropriate to the type of diving you'll be doing; shallow no-stop dives or dives where you go a bit deeper. It might be agued that the second type errs on the side of caution. I'd say it does no harm to hang around at 6m or less as might be mandated, provided you've got sufficient gas in your tank. Stay away from the edge!

Happy diving. - John Bantin

Diving Certification

We've all been wowed recently by the YouTube footage from those crazy guys who jump out of helicopters or off the tops of high mountains wearing nothing more than a wing-suit to aid their safe landing. They know the risks they take.

It's the same with lots of action sports. You can kayak over a waterfall or ride your mountain bike down an incredibly steep hill. You can even buy fishing gear and a lot of beer and go and sit at the edge of some deep water without anyone questioning whether you can swim. It's probably only the high financial outlay and the risk to the animal that people take horse-riding lessons. If it goes wrong you have no one to blame but yourself. It's down to you.

We live in a free country and there's nothing to stop you from buying a bike and riding it where others might blanche at the prospect. Neither is there anything to stop you from buying a full set of scuba gear and popping off for a dive alone in the ocean. That's your choice.

However, we also live in an age where safety has become paramount if there's any possibility of someone else getting the blame. This is why you need certification to embark on scuba diving if anyone else is involved with you.

After diving for more than thirty years, I was sent incognito by a magazine to enjoy a PADI Open Water Diver course at a dive school in the sun abroad. The object of the exercise was to write a feature about it.

None of the other would-be divers knew me and I noticed a certain level of apprehension the first morning among my wide-eyed companions. I too was a little tense since the course was to be conducted in German, a language I didn't speak. I bluffed my way through and my years of underwater experience meant that I became a star pupil once I fathomed out what was wanted of me.

Over the period of four days, my previously nervous companions visibly grew in confidence as they discovered that scuba diving was not nearly as difficult as they might have imagined. At the end of the course they were all certified.

We then spent the next few days doing some easy shallow leisure dives during which time it struck me that these people who had enrolled in the classroom on that first morning knowing nothing about diving had, in the course of a few exercises and dives, become within that short time frame, experts in their own eyes.

Assuming I too was a newly qualified open-water diver, between dives I got lots of uninvited advice about my equipment choice and where I should go diving. For example, I was told that I had the 'wrong' regulator and that I didn't need a diving computer.

Scuba diving is almost unique among leisure activities in that you need to embark on a structured course and are eventually issued with a certificate that proves your proficiency. Of course the PADI OWD certification is only the start. You can go on to obtain far greater levels of certification for more advanced levels of proficiency and whatever level you achieve there will always be someone with a higher level than you.

Scuba diving is not normally a competitive sport. Those that compete at the extreme level usually have only one destination. There are bold divers and old divers but few old bold divers. However, our human condition lends itself naturally to compete. When you learn to dive, you'll take on board everything your own instructor tells you. Inevitably, he will have his own personal take on things despite adhering to the training standards of his particular agency. Later, you will find yourself in the company of other divers who maybe learned slightly differently or with alternative training agencies. They are not wrong, neither are you.

Be warned that you will meet people who try to enforce their own opinions and points-of-view about diving technique upon you. Some will be worth adopting while some will suffice to merely aggrandise the teller. (The Internet is awash with the opinions of such keyboard warriors.) Learn to pick up new ideas but reject those that are merely a different way to skin the same cat. Don't be demoralised. You've got a certificate too.

It's the certification phenomenon in scuba diving that lends itself to those that want to prove themselves instant experts. Nobody tells the wing-suited flier he's doing it wrong. He'll know that, if he is, the moment before he hits the unforgiving hard surface.

Safe diving - John Bantin

Bantin's Blog!

For more than 21 years, John Bantin wrote for Diver Magazine. His articles were about diving experiences at diving destinations, diving techniques, his famous equipment tests and reviews, and even simple opinion pieces. His vast library of underwater pictures served not only to illustrate his own work but that of many others. He never shied away from saying what he thought even if it might be controversial. He always believed in engaging the reader emotionally even if it meant making them angry. He certainly made food for thought. Now he's promised to write a regular weekly blog for Mike's Dive Store. It will always be informative, entertaining and often thought provoking. We might even, one day, persuade him to tell us the back-story on why he walked away from what was apparently the best diving job in the world.

Diving With Sharks - John Bantin

Sharks

One of the first things non-divers ask you when you first embark on a scuba-diving course, is if you aren't worried about sharks? Everyone remembers their first shark encounter under water. Mine was lying torpidly on the seabed, undoubtedly a shark but disappointingly inactive nevertheless. It was a nurse shark. Later, I came across a white-tip reef shark. I was able to record it on my underwater Handycam because I managed to corner it in a cave. It swam round furiously looking for a way out before it escaped in a rush right past my ear. I found my heart was beating fast but the shark had been rather smaller and rubbery than I anticipated.

Years later, I went to my first shark feed. There were about a dozen proper shark-like sharks circling round while an intrepid dive guide fed them with scraps of fish at the end of a spear. This was an adrenalin-busting experience and limited to film in my camera, after a few minutes I'd shot my 36-frame ration and had to head up back to the boat to reload.

The sharks were still there when I got back shortly after and I shot a second 36-frames worth before again retreating to the boat to reload. It was incredibly exciting. These Caribbean reef sharks were as big as me and were inclined to bump into me if I got in the way between them and the hand-out of snacks. I rushed to reload my camera the third time and, in the excitement, failed to close up its housing properly. My heart was racing as I swam down to join the ominous grey shapes circling below but it raced even faster as I swam back up in a vain attempt to save my flooded camera.

I've dived in close proximity to many different types of sharks since then and photographed them too. Everything from the mass brawl of hundreds of little white-tip reef sharks squabbling over some unfortunate prey at night to the majestic whaleshark that hoovers up small fishes and plankton have been the subject of my lens. I've won prizes for my close-up wide-angle pictures of Great hammerhead sharks. Recently, a huge tiger shark, much bigger than me, grabbed my tank and swam off with me. It was a thought-provoking thirty seconds before I was unceremoniously dropped.

If you want to hear more about diving with sharks, what a great buzz it can be and where you can do it, come to my illustrated talk at the London School of Diving and Mike's Dive Shop Open-Day on Saturday 12th October at 2.00pm, next to Mike's Dive Store - click here for full details....

John Bantin