Saturday, January 14, 2006
Scuba Lesson #2
Today's lesson was about five and a half hours long. The first couple of hours were spent in the classroom, reviewing the quizzes for chapters 2 and 3 from the textbook, along with various other topics. We started the lesson by watching the climactic underwater battle from Thunderball, which the dive master happened to record last night. We wondered whether we would be taught how to use harpoon guns, how to drive self-propelled underwater sleds, or the best technique for cutting a SPECTRE frogman's air hose, but alas, this course doesn't cover such topics.
The in-pool exercises started with mask clearing. Next we learned to breathe from a free-flowing regulator. Regulators are designed such that when they fail, they will be stuck open rather than stuck closed, so you get a continuous flow of air out of the mouthpiece. It was surprisingly easy to breathe from it in that condition.
We practiced switching between the regulator and the snorkel while swimming at the surface, without raising our heads out of the water. I got a mouthful of water once when I descended a little while snorkeling. I suspect I'm going to have a lot of trouble if I ever go back to non-scuba swimming—breathing underwater seems natural to me now, and I'll never be comfortable holding my breath ever again.
Most of the water work was focused on buoyancy control. Most of the time, a diver wants neutral buoyancy, meaning that the diver stay at a constant level, but of course you need to ascend or descend sometimes. Buoyany is controlled in a couple of ways. First, a diver wears a Buoyancy Compensator Device (BCD), which has inflatable chambers. As the chambers are filled with air, one gets positive buoyancy, and by deflating the chambers, buoyancy is reduced.
The other means of control is by breathing. When you inhale, your lungs fill with air and you get positive buoyancy. When you exhale, the opposite occurs. So, by controlling the BCD and breathing, one can maintain a depth or make a controlled ascent or descent. The proper technique is to inflate or deflate the BCD appropriately, then use breathing for fine tuning. It's a bit like the trim tab on an airplane.
We did an exercise known as the "fin pivot." To do this, you descend to the bottom of the pool, lying on your stomach with arms outstretched like Superman. Then, when you inhale, your body should rise from the bottom, and when you exhale, your body will descend again, pivoting on your fins, which stay on the bottom.
I really like the buoyancy control exercises. You just control your breathing, and do nothing else. They have a very relaxing, meditative quality to them.
We practiced "tired-diver tows," where one diver drags or pushes another who is unable to swim. It is easier than towing a non-scuba swimmer, because the BCD's keep both divers floating on the surface, and the regulators allow the tower to swim without worrying about keeping either diver's head out of the water.
After getting out of the pool for a brief break, we did the "giant stride entry." This is how you often see scuba divers enter the water: they just stand at the edge of the water, take a big step forward, and fall feet first into the water. It always looked a little traumatic to me, but after doing it, I can see there's nothing to it. It doesn't take any skill: you just let yourself fall into the water, and then wait until you float back to the surface, breathing normally from the regulator the whole time. I think tomorrow we'll be doing the "back roll entry," where a diver flips over backwards into the water, which also looks difficult but now I suspect it won't take any more skill than the giant stride.
Finally, we got to dive to the deep end of the pool for the first time. All of the exercises up to this point were in four or five feet of water, but here we descended 12 feet. There was nothing difficult about it, but it was the first time I felt like a real scuba diver. Down at the bottom, we just played around. There were a bunch of weighted frisbees and other toys at the bottom that we threw between ourselves. The dive master laid on his back and blew bubble rings (like smoke rings, but underwater). We stayed down there for about ten minutes, then made nice slow controlled ascents back to the surface. Then class was over.
One lesson to go . . .