The final test-dive we had to complete/endure was a ‘real’ dive in deep water in a rock quarry in northern VA. The rock quarry had not been used in many years and had been long -filled in with water; therefore many dive agencies used this place to certify divers without having to head to the Chesapeake Bay or further out to the Atlanta, perhaps to Ocean City or somewhere similar.
I said ‘endure’ in the preceding paragraph because this experience was my first of many with something called a Thermocline, which is a certain depth where the water temperature drops quickly by 5 or more degrees within a few feet or even a single foot. Another term for this phenomenon is called Water Stratification. I found in this quarry that the thermocline occurred at about 15 feet. The activities we were to be tested on by our instructors were placed between 10 and 30 feet down; the cold dark quarry bottom being around 65 feet. This meant that we would need to go from the warmer water to the colder and vice versa. Soon after my giant stride into the water I found that I was to become a water temp wimp within the diving world. Personally, my preference is to remain in the cold water or the warm, and not go back and forth – if I go back and forth I feel like I am just being teased by the temperate water; like it is laughing at me or something! ARGH!
The instructor requested that we circle up and descend together to about 15 feet and achieve neutral buoyancy* there after which he wanted us to again remove our mask and reg and replace them properly after re-clearing them for regular use. While at 15 feet, I can feel my lower half (at 20’) getting colder and colder from the temp change but luckily my tasks don’t require anything of my lower half except the occasional fin kick. After this, we drop down further into the chilly depths (it’s amazing how dark the water gets in a quarry, even at only 25 feet down, even at mid-day) for the remaining tests. We see as we descend that there is a hula-hoop attached to a chain that drops down into the abyss. The hoop is not moving and we are signaled to swim over to it and demonstrate neutral buoyancy for 5 minutes. We were told that if our tank hits the upper side of the hoop we have to do the test over. No pressure folks! Luckily everyone passed but it was really amazing for me to see how much I had to control my breathing to maintain the necessary depth. What a great skill to learn! I would find application of it very often in my future diving in the ocean.
There were some other tests of note, but I don’t remember all the in’s and out’s of them from so long ago (it has been 10 whole years since my certification!!!) Amazing how time flies!
*Neutral Buoyancy, occurs when the diver doesn’t sink or float while at depth. More specifically, his/her body & gear weight equal the amount of air held in his/her BC. When this balance is achieved the diver will rise slightly when a breath is inhaled and sink slightly when that breath is exhaled. Any real upward or downward movement becomes an intentional act of the diver. Neutral buoyancy is a great skill to learn as it becomes invaluable on drift dives, for example: as the diver is carried along the bottom by the tidal current, he/she need only to inhale slightly to rise over an upcoming rock or coral outcropping (exhaling after passing over the structure to return to the optimal depth); doing this saves fin kicks, therefore decreasing the amount of air used during the dive (moving your muscles uses air) which increases bottom time.
No comments:
Post a Comment