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Author Topic: Effortless Buoyancy Control  (Read 2789 times)

Offline flopnfly

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Effortless Buoyancy Control
« on: March 12, 2007, 02:58:00 PM »
Effortless Buoyancy Control
 
    
 
 Less lead, less bubble, less trouble--use our foolproof system to find perfect weighting for every dive.
 
 
 Basic Skills: Effortless Buoyancy Control
 
 "No, I didn't see the damned seahorse, thank you very much." Nor, it seems, the cleaner shrimp or the spinyhead blennies or any of the tiny wonders that those other divers are chattering about on the stern deck--those divers who seem to be able to glide and hover like fish, poking their heads into holes with perfect ease. Meanwhile, I was playing tunes on my power inflator buttons trying to avoid crashing into the reef.
 
 Can we put two and two together here? The reason I wasn't seeing as much down there was that I was preoccupied with those "elevator buttons." I had lousy buoyancy control. "A lot of divers have trouble with that," says PADI instructor Len Wittrock. "But those who have really good buoyancy control tend to see a lot more, probably because they're not so distracted." Bingo. Oh, I could get neutral alright and I could control my ascents, so I got through the dive OK. But I was concentrating so much on diving, I wasn't getting much out of the dive.
 
 In those days, my buoyancy required constant maintenance because I was overweighted. Like many of us, I got my load of lead close enough to the right amount to function, but I never fine-tuned it. Ballpark weighting allowed me to get by, whereas precise weighting would have allowed me to forget about my buoyancy and enjoy myself. I should have spent the first few minutes of my dive at the platform getting my weighting right, but that sounded too much like cleaning my room before going out to play. Who wants to waste good dive time on chores? "Good enough, let's go!" was my motto then.
 
 I got smart only when I learned I could use the dive time that's bad, or anyway less good, for the housekeeping. I'm talking about the minutes "wasted" on that mandatory buoyancy check, usually from the resort's dock or off the beach, where there's rarely much to see anyway. And the three-minute safety stop at the end of the first real dive, when we often just stare at the countdown clock. Call it maturity, but I've learned to spend the time on a buoyancy check that gets me within a couple of pounds of my best weight every time, and a fine-tuning drill during my first safety stop that makes my buoyancy control practically effortless for the rest of the week. I think of it as doing my chores on their time, not mine.
 
 Foolproof Buoyancy Check
 
 Many of us shortchange the buoyancy check, partly because we're fresh off a plane ride from hell, still disoriented by the soft breezes and the warm water, and partly because nobody told us how to do it better. So we just pile on the lead until we sink and call it good. Of course it's not good, because we're juggling too many variables at once to come up with an accurate weight total. Our restless body, our wetsuit, the air trapped in the BC, the BC itself, and even the tank all have varying and unmeasurable effects on our buoyancy. Talk about herding cats. Instead, take it in stages:
 
 Step One:
 
 Leave the scuba gear on the dock. Go in first with just mask, fins, snorkel, wetsuit and your best guess of how much lead you need. Make changing weight easy. You can just hold a couple of weights in your hands, or carry a belt with weights looped through one slot. Float around awhile, look at the sand and concentrate on relaxing. Any unnecessary movement of hands and fins tends to push you upward, fooling you into adding unnecessary lead. Wait for your breathing to relax too. At first, you're probably holding too much air in your lungs, increasing your buoyancy. Take your time with this. After 15 minutes, you will be moving slower, breathing slower and therefore closer to your true buoyancy and weight requirement.
 
 Now add or subtract lead until you float with a full breath and sink when you exhale. When you've added enough lead to sink, take off lead again until you float, then add a pound. You'll never zero in on the exact weight until you pass it from both directions. If you float at eye level while holding your breath, that's about right.
 
 Step Two:
 
  When you've got the right amount of lead to compensate for the buoyancy of your body, your wetsuit and your snorkeling gear, adjust it to account for the BC, tank and regs. Many BCs have a little inherent buoyancy even after all the air is out of them. In testing hundreds of them, ScubaLab has found they range from zero to four pounds of positive buoyancy. Check past BC reviews at www.scubadiving.com for specs on your model, or just assume two pounds positive buoyancy, a common amount. Assume one or two pounds negative buoyancy for regs and console. The typical aluminum 80-cubic-foot cylinder is three pounds positive when down to 500 psi at the end of the dive. That's when you want to be neutral. Adding it all up, you might start with another three pounds of lead.
 
 Step Three:
 
 String the weights on your belt or load your pouches, put on your scuba gear and try your buoyancy now. Assuming a full tank, which is five pounds heavier than the one with 500 psi you weighted yourself for, you should sink easily. If you float, don't assume you need more lead. More likely, there's air in your BC. To get it out, hold the inflator hose over your head and stretch it upward a little so its attachment point to your BC is highest. (Gently: Don't stretch it so energetically that you pull it off!) At the same time, suggests Linda Van Velson, a PADI course director, "dip your right shoulder and squeeze the BC against your chest with your right arm." This maneuver encourages the last few bubbles to find the exit. Next, rock backward a little. Many BCs trap a bubble of air just behind your head. Rocking backward as if you were in a La-Z-Boy recliner moves the exhaust hose over the bubble and lets it escape. Even if the bladder is empty, pockets and padding can trap a surprising amount of air, so be patient. Remember to relax. Add lead only as a last resort. At this point, your weighting is close to minimum but still "ballpark," though it's a much smaller ballpark than if you had started with a buoyant BC on your back and had to deal with all the variables together. Fine-tuning comes later.
 
 Step Four:
 
 Time for a trim check. Trim is the position your body takes in the water when you're neutral and still. When fine-tuning buoyancy, this matters because if your fins are lower than your body, kicking to go forward will also make you go up. It will seem that you've suddenly become buoyant; to counter this, you'll probably vent air from your BC. Then, when you stop kicking, you'll be too heavy and you'll sink and want to add air. In order to keep your kicking from disrupting your buoyancy, your body needs to be trimmed so your legs are nearly horizontal and your fins push you only forward. Once you are exactly neutral with the right amount of weight, test your trim by holding your body absolutely still with your legs stretched out behind you. If your legs sink, you should move a little weight from your waist to a point higher on your body, like the trim pockets found on most BCs.
 
 Lateral trim is also important so you can lie on your side and look under a ledge, for example, without having to scull with your hands to hold this position. Any such sculling often makes upward thrust, which will have to be countered by deflating your BC--the same problem as fore and aft trim.
 
 Fine-Tuning at the Safety Stop
 
 Now you should be very close to your optimum weight and trim. Save the fine-tuning for that other "dead time," your three-minute safety stop at the end of your first boat dive. After 40 minutes or so of diving, you should be relaxed, moving slowly and breathing normally, and your tank should be as light as it's going to get.
 
 To fine-tune your weighting, you need to be carrying your smallest weight, one or two pounds, loose in a pocket or clipped to a D-ring so you can take it off easily. When you and your buddy are hanging out at 15 feet, hand the weight to him temporarily or put it on the bottom if the water is shallow. Get all the air out of your BC and see if you can get neutral. Remember to keep your hands and fins as still as possible. Do the test next to the mooring rope for security if you want, but remember, you can always overcome a pound or so of positive buoyancy by exhaling and kicking downward, so there's no reason to fear an uncontrolled ascent. If you can stay neutral at 15 feet without that small weight you took off, you didn't need it, and your next dive will be easier without it. Now retrieve your weight from your buddy and do the same favor for him.
 
 Try taking off another pound or two on the next dive. Remember, you won't zero in on the exact amount until you've taken off too much. After two or three days, you will be even more relaxed and can probably shed still more lead.
 
 Breath Control
 
 Now your weighting is at a minimum and you can control your buoyancy with your lungs alone most of the time. Your lungs are, in effect, another BC with a maximum buoyant lift of about 10 pounds. That's the difference between a deep inhale and a full exhale. A normal, relaxed breath causes a buoyancy shift of about one pound, which is hardly noticeable. This means you can select any amount of lift you want up to the maximum by breathing gently from mostly full lungs, mostly empty lungs or anywhere between. Your lungs are a great BC, by the way, and underappreciated. They boast hands-free operation, with no buttons to get stuck or confused, they require no maintenance and they're free.
 
 One tip on their operation: Be patient. Water is a viscous fluid, more like molasses than air, so your body won't respond immediately to buoyancy changes. When you want to ascend a little, you'll have to inhale and hold your breath for a few seconds before anything happens. This is why many divers don't realize the value of their natural BC. They breathe in and out so rapidly that the resulting buoyancy changes don't have time to take effect.
 
 You're not quite done with the power inflator, though. Your tank will gain about five pounds of buoyancy as you breathe it down to 500 psi, so you'll have to vent five pounds of air from your BC. But that's a slow change, say one pound every 10 minutes, and will require only a couple of adjustments during your dive. Your BC (assuming some air in it) and your wetsuit also gain or lose buoyancy as you change depth and will require compensating adjustments on those buttons. These changes are greatest in shallow water. Below 60 feet they may be almost negligible because neoprene is almost completely compressed by then. And if you needed another reason to get on a plane for the tropics, one advantage of warm water is that you need very little neoprene, so you have very little buoyancy shift to deal with.
 
 There are other ways to reach minimum weighting and effortless buoyancy. Taking a specialty class is one. Just try something-- because the payoff is big.
 
 Crash Dive!
 
 Basic Skills:
 
 Effortless Buoyancy Control
 
 With minimum weighting, the first five feet of descent can be difficult, until pressure forces the residual air out of your wetsuit and starts compressing bubbles. Some divers force the five-foot barrier by making a head-first surface dive on fin power. Here's the technique:
 
    1. Float on your stomach, legs stretched out, arms to your sides.
 
    2. Jackknife your body so your head points to the bottom. Sweeping your arms forward from your sides will help.
 
    3. Immediately, raise one leg, then the other, high in the air as if you were doing a handstand. The weight of your legs in air will force your body straight down.
 
    4. When your fins are underwater, start finning down while holding the auxiliary air dump on your BC open.
 
       The trick is to get the timing down so steps 2 and 3 come in a rapid, fluid motion. It may take some practice.
 
 If you can't equalize your ears easily on a headfirst descent, try a feet-first alternative often used around kelp. SSI Instructor Certifier Pat Dunn describes it: "Scissor-kick up with your fins to raise yourself out of the water as high as you can go, then lift your arms above your head and let the weight of your arms and torso, plus your downward momentum, push you under until you are deep enough to be able to swim away."
 
 Does Five Extra Pounds Really Matter?
 
 The math is surprising. Every extra pound of downward force requires a pound of upward force to balance it. That means displacing a pound of water with a pint-sized bubble--"a pint is a pound the world around." But because an air bubble expands and contracts with depth changes, you have to be constantly adding air to the bubble or subtracting it to keep its volume at one pint. Five extra pounds of lead, which is common, means a bubble five times as big and requires five times as much dancing on the power inflator to keep a constant volume. On the other hand, less extra weight means a smaller bubble, which has less effect on your buoyancy when it grows or shrinks.
 
 Let's assume one pound of buoyancy change is a threshold. Gain or lose more than that and you have to do something about it pretty quickly. How far could you ascend from 60 feet and gain only one pound of buoyancy? Boyle's Law says if you were one pound heavy and therefore needed a one-pint bubble in your BC to be neutrally buoyant, you could ascend 47 feet (to 13 feet) before that bubble gained another pint of volume and pound of buoyancy. But five extra pounds of lead requires a five-pint bubble, which gains one pint (and pound) in only 15 feet of ascent (to 45 feet). In this case, eliminating four pounds of unnecessary lead gives you twice the latitude for error in your buoyancy control.
 
 Why Are Some Divers Heavy?
 
 SUBSTANCE    SPECIFIC GRAVITY
 
 Fat    0.7 - 0.9
 Freshwater    1.0
 Seawater    1.03
 Muscle    1.08
 Bone    1.9
 
 Two divers, both six feet tall and weighing 180 pounds, may require very different amounts of lead. The reason? Muscle sinks, bone sinks, but fat floats. So the lean, big-boned athlete will need less lead than his couch-potato "twin." Specific gravity is weight in grams divided by volume in cubic centimeters. If it's more than 1.03, it sinks in salt water.
Twenty years from now you will be more disappointed by the things you didn't do than by the ones you did do. So throw off the bowlines. Sail away from the safe harbor. Catch the trade winds in your sails. Explore. Dream. Discover.


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