One of the motivations for writing 66 Metres was wreck diving. I've dived wrecks in many different parts of the world, and I am always fascinated by seeing these graveyard ships, imagining how they were before, and witnessing how nature colonizes them, turning even warships into havens for fish and coral.
But they are often spooky, approaching out of the gloom. And there is always an amount of added danger, from becoming lost or getting trapped inside one, to catching a limb on a jagged edge and cutting yourself (never a good idea in shark-infested tropical seas), to finding poisonous fish (e.g. stonefish or scorpionfish) lurking just where you may need to put your hand...
Often the visibility is actually better inside a wreck than outside it - that is until someone kicks up the thick layer of silt carpeting most wrecks. Within seconds almost perfect visibility can drop so you can barely see your outstretched arm.
Much of the diving in 66 Metres takes place in the Isles of Scilly, which has a huge number of wrecks. I dived there many years ago, and it wasn't without incident. On one dive, my buddy and I were inside a wreck at around 40 metres, and had attached a line to the external part of a wreck. On the return from the bowels of the ship (aka the engine room), I reeled the line back in only to find that somebody (we never found out who) had untied it, potentially stranding us inside. On another dive, one much like the Tsuba described in the book, we got separated, and there was much frantic searching at a depth of nearly fifty metres before we found each other again. Not much reserve air left on that dive!
On a third dive there, my buddy and I found a small hatch to a separate chamber deep inside a wreck. I wanted to see what was in there. But the only way I could do it was to take off my stab (buoyancy) jacket and air tank, go through the hatch, and put it back on as soon as I was on the other side. My buddy could read my mind apparently, because she just looked me in the eye and shook her head slowly. So, I didn't do it. But I always wondered what was in there... And in the book one of the two protagonists, Jake, has to do exactly this maneuver. It doesn't go well...
When wreck-diving, it's important to touch as little of the wreck as possible. One of the worst things you can do is to pull yourself along, using the ship's metal as handholds, because if the wreck is rusted away, it may need only one small tug to bring the ceiling crashing down on you. Again, this happens in the book to two inexperienced divers, and the book's heroes have to try and figure out a way to rescue them before their air runs out.
I've also had a lot of fun on wrecks, for example watching three barracuda hunt inside the SS Yongala near Townsville in Australia, and just having fun diving some of my favourite wrecks on the west coast of Mauritius or in Scotland (the Hispania is one of my favorites), and of course the Thistlegorm in the Red Sea, where I always manage to sit on one of the motorbikes in its hold. You never know what you will see on a wreck. On my very last dive in Hawaii, a stone's throw from the buzz of Honolulu, I descended down a line to a pristine wreck at thirty metres, and there on the foredeck were four large turtles just sitting there, like they were playing cards. They looked up at me slowly as I descended. I just started laughing, and then nearly cried as I realized the battery had died in my underwater camera. Who was going to believe me?
66 Metres is available from Amazon and also currently from Sainsbury's for a limited period.