Sunday 29 August 2010

Stoney Cove, Part the Second

We hung around passing our surface interval* time by discussing the previous dive, sheltering from the rain beneath the car boot lid, and consuming hot chocolate and ham and spready cheese sarnies. After two hours had passed, we strapped ourselves back into our gear, ready to tackle our next dive.

We'd decided to do a shorter dive to take in the Stanegarth, then practise our navigation skills by trying to find the new attraction, the Belinda (another sunken ship). We finned out to the buoy marking the Stanegarth, then descended the line from the buoy to the wreck.

Or, in my case, tried to. I remember thinking "This descent is taking a while", then looked at my computer and realised I was actually shallower than I had been one minute previously. I'd got disorientated as there were no visual references to help me judge whether I was going up or down, just the surrounding green murky water and the white shotline. Fortunately S was in attendance to help guide me down to the wreck, where I would like to say I landed elegantly on the deck, but in fact the phrase "crashed into it and then floundered about inelegantly getting pulled off-balance by the 15L tank I wasn't quite used to yet" would be more accurately. I was really annoyed with myself for buggering up whilst diving with two more experienced divers, but you can't let these things bother you under the water, it spoils your concentration and the dive. It's all a learning experience anyway.

We descended into the interior of the Stanegarth, which, technically, was breaking the rule against not going into overhead environments without equipment and training. On the other hand, the wreck itself is so small you can't get lost, but not so small you are going to get stuck, and has multiple easy exits including a large overhead hatches, so we went in. It was the first time I'd been inside a sunken ship, and it was rather cool, spoiled only by the realisation that my new underwater torch was (hopefully) still sitting on the side of the dock. Bugger! (The photo on the left, which I didn't take, shows the Stanegarth.)

We swam around the Stanegarth, then took a compass reading of 140 degrees and headed off to find the Belinda. After three minutes, a ship loomed up before us, and I remember thinking "Hey, we're getting good at this navigation lark!"

Then I read the name on the front of the ship - Defiant - and thought "Hmm, maybe we're not". On the other hand, we got to see the Defiant, then S made a hand signal I hadn't seen before, of crossing her hands in front of her chest to form a large 'X'. I interpreted it (correctly, as it turned out) as meaning "Time to end this dive".

M sent up a surface marker buoy to give us a line to help with our ascent from 22M - or tried to. I am not an expert on their use, but it was pretty obvious from the fussing of M and S that it was not working the way it was supposed to. Instead, we made a free ascent (an ascent with no visual reference except your computer or depth gauge), finning carefully to maintain our position at 5m deep for a 3 minute safety stop**. We broke the surface and S gave her opinion on the SMB, which I shall reproduce here as "it's not working very well".

We decided to use up our air by finning over to the 7m shelf near the dock, descending to the Nautilus (a model of Captain Nemo's submarine, shown in the photo I didn't take on the left) and feeding the fish with a plastic bag of sweetcorn which M had in her buoyancy jacket for this particular purpose. We descended, looked at the sub, fed the fish, and submerged to find my torch sitting where I'd left it. S advised me to get a clip for it to secure it to my jacket, which I have since done.

We wandered over to the shop, where I realised that I must be a diver. Some women impulse-buy shoes. I impulse-buy big steel bottles full of air. Stoney Cove had some 12L tanks for sale at a very reasonable price, and I decided that hmm, yes, I did want to stop paying £10 to hire a tank every time I want to dive. I purchased the tank, the mesh to protect the paintwork, and the magnetic "compressed air" sign to go on the back of the car. We said our fond farewells, promised to dive together again soon, and I loaded tank, self and dive gear into the car, and headed North and home.

* time on the surface inbetween dives. Necessary to allow your body to "off-gas" i.e. eliminate the nitrogen dissolved in your tissues following the dive. This happens through respiration. The ambient pressure at the surface is lower than when submerged, and whilst you're at the surface, the nitrogen slowly moves out of your tissues, goes into the bloodstream, and is expelled through the lungs. "The bends" happen when you have nitrogen dissolved in your body tissues and move too quickly from being at greater pressure (which keeps it dissolved in your tissues), to being at lower pressure, when it begins to move out of your tissues in bubbles which are too large to safely pass into the bloodstream and do damage to the body on their way out.

Surface intervals allow you to eliminate dissolved nitrogen in between your dives, allowing the second dive to take place safely and giving you more time under the water. If you still have nitrogen dissolved in your tissues from a previous dive, future dives have to be shorter, so that you don't absorb so much nitrogen you can't safely eliminate it without doing decompression stops - which, as a recreational diver, I'm not trained to do (technical divers do decompression diving, recreational divers are not trained for it and don't have the gear to do it safely).

** safety stop. A 3 minute pause at 5 metres deep at the end of a dive to allow dissolved nitrogen to move slowly out of your tissues at a safe rate - the 5m depth maintains sufficient ambient pressure than the nitrogen does not move as quickly out of your tissues as it would at the surface. Differs from a decompression stop because it is not mandatory. Theoretically, you could skip the safety stop and, provided you kept your dive within the no-decompression depth and time limits, you should be safe from the bends. ("Should be" because all divers differ in their physical size, fitness and breathing rates, hence the theoretical models used to calculate no decompression times do not necessarily fit all divers exactly the same.) A decompression stop is required, in the sense of "if you don't do this you'll get the bends".

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