Canal boats, dinghies, ocean liners and yachts. What about them? Well, they're all types of water-going vessels that can be conveniently covered by the umbrella noun, boat. Yes, they all have their subtle differences, but one thing that they all have in common is, in my eyes, a very careless design flaw. They have a tendency to sink. When they do sink, it's mightily inconvenient for all involved, not least to those who are on the boat at the time. I'm sure Lloyd's of London are probably sick to the back teeth of the entire situation as well. So let's face it, as soon as someone invents the unsinkable ship, we'll all be better off. Assuming, that is, that they don't make a movie about it staring some podgy bloke with fluffy hair. But until then, some make the best of the situation by strapping an air tank to themselves, throwing themselves in the water, and going to take a bit of a look-see at the wreck lying in its watery grave. They call this recreational pursuit... wreck diving.

Original, I know.

Of course, the wreck isn't always a boat; it can be a plane, car, train... anything manmade that's been sunk to the bottom of a body of water. Quite often, these things have been sunk purposefully after being stripped of all salvageable parts. Far from being an extreme version of littering, these wrecks become a part of the water's ecosystem. Depending on the temperature and type of water that they've been sunk in, they may form artificial reefs that are teeming with sea life, and since a ship that sank in warm tropical seawater will deteriorate quite quickly (a lot quicker than one that sank in cold fresh water at least) it eventually just forms a background to the coral, rather than being a feature in itself. However, not all wrecks are intentional ones, and there are many ships on the bottom of the oceans that are still full of the cargo and fittings that were on board when they went down. This can be a problem in vessels that are carrying large quantities of fuel or oil on board, which will gradually begin to leak out into the water as the ship decomposes and collapses down. To prevent this massive ecological disaster from occurring commercial divers trained in deep-sea diving will often dive on these wrecks to pump the oil and fuel out, and to recover any valuables that may have gone down with the ship. These are the more dangerous wrecks to dive on; all the ship's fittings are still in situ and there will be rotting furnishings, narrow corridors, and various other hazards for the unwary diver to fall prey to. Of course, these are often the most interesting wrecks to dive for exactly the same reason.

Why dive wrecks?

There are many different reasons why someone may choose to dive on wrecks as a hobby. For some, it's the sea life that a wreck attracts that provides the incentive; a wreck will provide a perfect habitat for many fish and other marine creatures, concentrated in a small area, which is perfect for those with an interest in underwater ecology. Another reason that people may dive a wreck that is linked to this is the opportunity that wrecks provide for underwater photography. As well as all the pretty fish to take photos of, the wreck itself can provide a distinctive and dramatic background for photographs. Some people dive a wreck out of an interest in its history; often they will have researched the wreck and the circumstances of its sinking in the local libraries and similar before diving on it. And others still dive wrecks just out of sheer curiosity, the tingling excitement of exploring somewhere that used to be an everyday part of life, but that is now cut off and out of bounds to those unable to survive underwater for long periods of time. The large variety of locales, water conditions and wreck types means that this isn't a hobby that's easily exhausted of subject matter.

Are there any wrecks that I shouldn't dive on?

Not all wrecks are diveable. There are two types of wrecks that divers are required by law to stay away from: wrecks considered to be of historical significance; and wrecks that have been designated as being war graves. Wrecks of historical significance are either wrecks that have a known historical significance, such as the Titanic, or wrecks that are more than 100 yrs old, such as Roman cargo ships. These are very loose guidelines; not all wrecks of historical significance are off limit, and it is best to check with a local dive shop before diving on the wreck. Artefact recovery from these wrecks is, however, strictly forbidden.

Many of the ships that went down in the World Wars went down with everyone on board, and as such, are considered off limits to divers, as they are essentially someone's final resting place. Again, as with wrecks of historical significance, not all war graves are off limit, and it is best to check before you go diving. If you do come across some human remains, have some respect and leave them be. If you believe that you're the first person to have come across them, contact the local authorities, who may decide to remove them for reburial elsewhere.

Wreck diving training

It is important that a diver is fully trained in the methods of diving on a wreck before doing so; this does mean doing an extra course in addition to the basic access scuba certification provided by organisations such as PADI, BSAC, CMAS or NAUI. The ability to recognise and avoid wreck-specific hazards that can turn day's diving into a tragedy is a key part of this training. I warn you now that if you choose to do the PADI wreck diving course, they will use the word 'penetration' many, many times during the video; if you're as infantile as I am, this will mean that you spend most of the two hours giggling like a school child. Hehe. Penetration. Sharp objects – cuts and abrasions are a common consequence of diving on wrecks; I myself am currently sporting a fantastic scar on my upper left arm that I'm actually quite taken with, courtesy of a Japanese shipwreck in Guadalcanal. For the most part your exposure suit will protect you against most scrapes, but don't forget how expensive exposure suits are; it's better to be careful and save yourself the cost of repairing the damn things. Rusted metal, torn steel, broken glass and splintering wood are all part and parcel of diving on a wreck; keeping your tetanus shot up to date is a well-advised move. Entanglement – because they attract a large amount of marine life, wrecks are often covered in bits of fishing line and nets, which are usually just an annoyance for a superficial tangle, but are potentially fatal if you get properly wrapped up in them. Always carry at least one diving knife with you when diving; my personal tip for the top is to buy yourself a pair of cheap strong, durable shears from a hardware store. Yes, they will fall apart after about a year's worth of diving, but on the other hand, they're not as expensive as diving knives, you don't need to keep them permanently sharpened, and most importantly, it's a lot easier to cut line with shears than it is with a knife. Unstable structure – a wreck is in a constant state of decomposition, and is slowly, but surely, collapsing in on itself. Just hope to God you're not inside it when it does. Things can dislodge from above or come away in your hand while you're pulling yourself along, and this is as true for outside the wreck as for inside. Funnily enough, things coming away unexpectedly in your hand is exactly as embarrassing underwater as it is on land. And if it's half a bit of ship, you're not going to be able to put it back where it was without anyone noticing what you've done. Trust me on this. Surge – tidal movements of water can result in areas of suction through holes and hatches in the wreck that, if you get caught in one, are at best embarrassing and at worst fatal. Aquatic life – it's not just Jaws that's after you; there's a whole variety of sea life out there that you don't want to catch the ugly side of that inhabit wrecks. To make it clear, there's very, very few sea creatures that will actively go for you, but there are more than a few that will get pissed off with you when you stick your hand in their home. Getting lost – once inside a wreck, it's very easy to become disorientated and lose your sense of direction in a maze of unfamiliar corridors. If the wreck is lying on its side, you can even become disorientated as to which way's up. Never dive a wreck without a reel and line to help you find your way out. Many divers have died because they were unable to find a way out of the wreck before they ran out of air. Enclosed spaces – if something were to go wrong with your equipment whilst you're inside a wreck, you haven't got the option of an immediate ascent to the surface; the only way up is by getting out first. Always keep your equipment maintenance up to date. Small / dead-end passageways – it pays to avoid passageways where your ability to turn to exit is compromised. Silt – a silt-out is exactly like being blind, leading to disorientation and loss of direction.

Wreck penetration equipment and techniques

If you're just diving around the exterior of a wreck and have no intention of going inside, then the extra equipment needed is minimal; in addition to your normal gear, you may wish to bring along a dive light to use for peering into the ship. However, for a penetration dive, you will require:

• Multiple dive lights – experienced wreck divers always carry at least two diving torches when doing a penetration dive; preferably they carry four. It's a simple case of mathematics. Even for a 99% reliable dive light, there's a 1 in 5 chance that the light will fail within 25 dives. For two lights, the chance of them both failing drops to 1 in 16, and for four lights the chance is about 1 in 6450 that all four will fail on the same dive within 25 dives.
• Line and reel – a line provides a visual / tactile reference to exiting a wreck. In the manner of Hansel and Gretel, a diver will tie off the line on a stable structure exterior to the wreck, and will then wrap the line around various structures inside the wreck at regular intervals as they proceed along. As they exit, the line can be reeled in, hopefully without tangling up.
• Slate and pencil – useful, both to carry a map of the wreck you're diving, and to use to communicate with your buddy, especially in areas of restricted movement.
• Pony bottle – a small reserve tank that comes in useful as an additional safety margin should you become low on air while still in the wreck.

There are three important guidelines for diving on a wreck that only the foolhardy would ignore. The first, and most important, is the rule of thirds: use one third of your air supply to get down to and enter the wreck; one third to exit the wreck; and the final third to act as a safety margin in the event of an unforeseen problem. Remember, when you're trapped in an enclosed space underwater, air = time to solve the problem and get out. The second rule is that you should never proceed further into the wreck than the edge of the light zone, i.e., don't go any further in than the natural light does. Lastly, never exceed a linear distance of 40m from the surface. So, if the wreck lies at 25m, you shouldn't go more than 15m into the wreck.

These guidelines have all been established with safety in mind; people regularly break them, but then people regularly drink and drive, or cycle without a helmet. Most of the time you may get away with it, however, there's going to come a time that you won't. Don't get me wrong, I truly believe that life is all about taking risks; but some risks aren't worth taking. I'd never go climbing without a rope and harness, I'd never go hiking in the wilderness without telling someone where I was going and when I'd be back, and I'd never dive on a wreck without keeping my safety (and that of my buddy's) as the number one priority.

I love wreck diving; I like researching the history of the wreck before and after I dive it; I enjoy exploring the wreck during the dive; I enjoy trying to piece it all together as to what went where and what did what; I enjoy finding (but not taking) small items that went down with the wreck, such as medicines, bottles of alcohol, and, in one wreck, condoms; and finally I am a complete ghoul and often wonder if I won't happen across some human remains. That last one does happen occasionally (though not to me); most of the time the remains are of previous divers who weren't as careful as they should have been and paid a high price for it. Moral of the story? Keep your dive experience up to date, your equipment well maintained and do a proper wreck diving course before you decide to go in and take a look.

Sounds great! Where do I go to do it?

There are many popular wreck diving sites out there; far too many to mention in fact. The best sources to go to for information on wreck diving sites are the local dive shops and dive boats in the area where you intend to dive. Another good source of information are diving magazines, which often feature some detailed information and maps of a particular wreck. However, there are some diving areas out there with a veritable excess of wrecks if you're the type to be like a kid in a candy store:

• Bermuda – the site of the infamous triangle, there are plenty of wrecks, some dating back almost 400yrs, to go explore.
• Graveyard of the Atlantic – off the coast of North Carolina lies a stretch of water that has claimed many ships over the years, including many from both the World Wars.
• Great Lakes – the North American Great Lakes make for interesting diving as they are cold freshwater, the perfect environment in terms of wreck preservation.
• Scapa Flow – lying near the Orkney Islands off the tip of Scotland, this is the resting place for numerous WWI and WWII wrecks, some of which are designated as war graves and are thus off-limits, but many others are open for divers to explore.
• Truk Lagoon – located near Papua New Guinea, this lagoon is the graveyard of more than 50 Japanese ships that were caught by Allied aircraft. Some of these wrecks are accessible by recreational divers, and the warm tropical waters guarantee a coral paradise for those that do venture into the water.

Reference

• PADI Wreck Diving training manual