潛水乜野最重要

以前，考完A仔，我亞sir問過我地覺得潛水乜野最難，我記得當時我話係Fin. 因為覺得好花氣力，自己氣力又唔夠，特別遇到頂流，Fin來 Fin去都好似唔去咁．但亞sir 話係Buoyancy 最難．

現在覺得佢好有道理，因為原來 Buoyancy 控制得好係好重要！最重要是不會炒底，撞死D珊瑚，又或者挍到D水濁晒！盡量用個肺嚟控制升降，唔洗又bump氣又放氣，咁就會好慳氣，就可以潛得耐D．Buoyancy 控制得好，睇野同影野都輕鬆D，呼口氣就落去睇野，睇完吸口氣就走．唔洗手手腳腳郁晒．再加上個 trim做得唔阻水，浮平D個人，咁就既慳氣又慳力．

Better Buoyancy

One of the key traits of an experienced diver, good buoyancy control is necessary to avoid damage to the coral we all pay so much to see, and to prevent uncontrolled ascents. It also allows you to relax and to reduce your air consumption. Do this:

1. Make small changes. And then wait for them to take effect. Are you sinking? Add a short burst of air to your BC and wait five or 10 seconds to see what happens. Even if you added exactly the right amount of air, it can take that long for the extra buoyancy to arrest your downward momentum and bring you to a stop.

One of the most common mistakes is to keep adding air to your BC until you begin to feel a change. By that time, you have almost certainly added too much air to your BC and will have to dump much of it. If you keep dumping until you again feel that you're not rising, you will have dumped too much. You can continue to yo-yo around perfect buoyancy all day.

Obviously, you have to use some judgment here. If you are very heavy and sinking fast, you will have to act more aggressively to stop your descent. That's even more true if you are ascending rapidly. But most of the time, most divers miss neutral buoyancy because they over-correct.

2. Minimize your weighting. Too much lead on your weight belt means you'll carry too much air in your BC to neutralize it. That would not be a big problem if your depth remained constant, but it doesn't. When you ascend, the air in your BC expands and becomes more buoyant, accelerating your ascent. When you descend, the air compresses and becomes less buoyant, accelerating your descent.

Neutral buoyancy is like the flat spot on a hilltop where a ball will not roll. Once it's pushed from that spot in either direction, however, it gains speed. Too much lead on your weight belt, and therefore too much air in your BC, makes the flat spot smaller and the slope on each side steeper.

The correct amount of weight is that which makes you neutral at 15 feet with an empty BC and nearly empty tank--so that you can comfortably hover at your safety stop. That means you'll have to be about four or five pounds heavy at the beginning of the dive. (The difference is the weight of air you use during the dive.)

3. Use your lungs. Once you've found neutral buoyancy, don't mess with it. Instead of adding air to your BC to make temporary changes--to hop over a boulder in your path, for example--add air to your lungs. Breathing from lungs mostly full can give you as much as two pounds more buoyancy than breathing from mostly empty lungs. Don't hold your breath by closing your throat, however. Maintain the greater lung volume with your chest muscles.

4. Anticipate buoyancy changes. Your buoyancy will increase the moment you start ascending, so begin venting your BC immediately. If you wait until you sense positive buoyancy, you will be playing catch-up and will probably find yourself over-correcting.

Likewise, you know that your BC and your exposure suit will compress as you descend, making you more negative. Add small amounts of air to your BC soon after you begin your descent so you don't become too negative.

As you breathe down your tank, you will become four to six pounds more positive by the end of your dive. Anticipate this, and vent small amounts of air from your BC to adjust for it.

5. Relax. Anxiety usually reveals itself in constant sculling with the hands and minor finning. In the normal, face-down diving attitude, this usually results in upward thrust. That upward thrust has to be balanced by additional lead on the weight belt, which is one reason why inexperienced divers are so often over-weighted. They think they are neutrally buoyant because they maintain a constant depth, but in fact they are constantly swimming upward.

You will never know if you are in fact neutrally buoyant until you can completely relax in the water. One test is called the "Buddha hover": sit cross-legged holding your fin tips (that keeps both hands and feet occupied). If you're neutral, you can ascend or descend by changing your lung inflation.

But Never Do This
In trying to minimize your weight, never remove so much lead that you cannot stay neutral at 15 feet at the end of your dive. That means you should be four to five pounds heavy at the beginning and should sink slowly even while inhaling.

There are even times when it would be wise to be a couple of pounds heavier than that. For example, when using a thick wetsuit for the first time, the neoprene itself will cause large buoyancy changes and if you are not careful in venting your BC as you ascend, you may need the extra lead to bring your ascent under control.

 

其他link:

http://www.scubadiving.com/training/basicskills/TN_basic_effortless_buoyancy_control

http://www.scubadiving.com/training/basicskills/6_secrets_of_buoyancy_control