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Rocket Science and Divers with a Limp
BobHalstead - 4/29/2013 8:33 AM
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Category: Educational
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By Bob Halstead

A few years ago I witnessed the launch of a Polaris submarine missile from underwater. At least that is what I thought it was at the time. There was the terrifying noise of exploding gasses and a dark shape whizzed past me shooting for the surface. A short time later there was a massive splash, that I could feel as well as hear, signalling that the launch had failed, and the missile had fallen back into the sea.

Turns out it was just a diver successfully putting some air into his new safety device called an “Adjustable Buoyancy Life Jacket”. These days we call them Buoyancy Control Devices (BCDs). Some people still regard them as safety devices in spite of reports that over 50% of Recompression Chamber treatments for decompression Illness are made necessary by out-of-control ascents. You put some air into your BCD, you rise a bit, the air expands and you rise a bit faster, then you fail to find the right button to push, or cord to pull, or you are in the wrong position – you cannot get rid of the now rapidly expanding air and next thing you are through the surface en route to the moon.

Manufacturers were so impressed by this phenomenon they decided to make bigger and better BCDs – with 25 kg buoyancy – with 30 kg buoyancy and yes, top of the range, 40 kg buoyancy. Aim for the Stars!

Now I admit I learned to dive in the tropics where neoprene wet suits were not really needed, and we never used BCDs – there were none – though at my NAUI Instructor course in 1970 in the Bahamas I remember some of us thinking we were very smart by using aircraft life jackets.

I learned to control my buoyancy underwater by using breath control. The only other thing that affected my buoyancy during the dive was the air used from my tank. This made me more buoyant as the dive progressed by about 2-3 kg but my lung volume of 6 litres plus gave me a range of control that could easily compensate for this. And anyway I planned to go down at the beginning of a dive and up at the end (I really recommend this plan).

There was a problem if I was salvaging treasure. By the way, treasure is anything man-made you find underwater. If you found the same thing in your back yard, it would be junk. Lugging treasure back to the surface was hard work, and it did slow the ascent. In fact it was often necessary to rest a bit on the way up, and I guess this is how decompression stops were invented. You see we found that if we stopped on the way up it was possible to walk around on the boat after the dive instead of falling into a bent heap on the deck yelling things such as “There is pain in my joints!” or “My arm has gone numb” or “I cannot get an erection”.

But I digress – I eventually found myself diving regularly in water only 25-6 deg. C (brrrr!) so got myself a full wet suit. Of course this changed my diving completely. First I found I could not sink so added lead to the belt – then I discovered that if I got to the bottom at say 30 m I could only carry half the treasure I normally carried if I wanted to get off the bottom. So I tested the wet suit and found that it had a buoyancy in shallow water of about 6 kg but at 30 m this was reduced to about 1.5 kg. In other words the wet suit caused a buoyancy change of about 4.5 kg. To control this a Buoyancy Control Device was needed with a lift capacity of 4.5 kg. Building in a massive safety factor, I went looking for a BCD with 10 kg lift.

It took a long time but eventually I found one, and I use it today. If I ended up on the surface after a dive in need of a life jacket (has not happened yet, but it could) I have 10 kg of useful buoyancy in my BCD plus what I would gain by dropping my weight belt, and with a wet suit that is another 6 kg or so. Seems plenty to me. If you still have a monster BCD with 30 kg or more buoyancy my advice is to get rid of it – unless of course you wish to contribute to rocket science.

It took a while but by the late 1980s manufacturers realised their BC’s were mostly far too big and more streamlined models became available. I hope my complaints, a voice among many I am sure, had some part to play in this advance.

Which brings me to divers with a limp. I did not say a limp WHAT, but Master Underwater Photographer David Doubilet, in his wisdom, pointed out that to save sharks from being finned we needed to get men to understand that shark fin soup causes impotence. In women it causes some equally terrifying calamity (I will not presume to offer a suggestion). OK so here it is – if you get bent you might become impotent (or “x” if female). Is this TRUE? Who cares? It absolutely COULD be – now are you willing to take the chance?

There are many things to do to avoid getting “bent” but the most important has proven to be “come up slow and stop on the way”

Forget about the useless, outdated, dangerous and arbitrary concept of NO-decompression diving and make EVERY dive a “decompression dive” with a stop of at least 5 minutes at 5 m even if your computer says you do not need to stop. I would be willing to bet that “NO-decompression” diving has bent more divers than any other single factor. And here is a message for the computer manufacturers – when are YOU going to acknowledge that every dive is a decompression dive, and therefore program your computers to have a stop automatically appear as soon as the diver descends past, say, 10m. No More Limp Divers!

On most boats, divers are advised to make a “safety stop” after each dive, but personally I think that is the wrong term – as far as I am concerned the stop is essential, not an added safety factor. Many boats have a convenient weighted bar hanging beneath the stern, or a weighted shot line, to give divers something to hang on to and make the stop easy, but I also recommend that, where the dive site allows, the stop is simply made on a shallow section of the reef near the boat. It is more interesting and leads to extra time on the stop instead of not enough. In most cases this is possible.

I also advise making a deep stop at about half the maximum depth of the dive if you are directly ascending from depth – as opposed to a multi-level dive where the depth has been gradually decreasing. It is a good discipline to stop at this depth, just for one minute, to check your buoyancy before it has a chance to get you into trouble, check all your gauges, and remind yourself of the plan for the final ascent.

Do not forget to practice using that BCD so that you can always dump the air when you need to – after all there is no guarantee that you will not be right under the boat when you find yourself emulating a Polaris missile, and that means you will …. Hey, I’ve just realised what “x” is – an everlasting headache!