Bcd Buoyancy
Bcd Buoyancy How does a SCUBA BCD work? OK, so you shoot some air into the BCD, and it makes the diver more buoyant, right? But aren't we talking about the same amount of air...just moved from t...
Bcd Buoyancy
 How does a SCUBA BCD work? OK, so you shoot some air into the BCD, and it makes the diver more buoyant, right? But aren't we talking about the same amount of air...just moved from the cylinder to the BCD? Does buoyancy change that dramatically when the air is no longer compressed? Archimede's Principle says that when a body is immersed in a fluid, it's subject to a force up-warding. The intensity of this force is given by the volume of the body and an equivalent mass of water. Everything has a volume and a weight. If the ratio of volume and weight in liters and kg is 1, then we have something that weights like water. If it is less than one, it means that it's heavier than water, if greater than 1 it is lighter. A fully equipped scuba diver (suit,weight, tank, bcd,regulators) can weigh about 100 kg (more or less 200 pounds). That means that there is a force that pulls him downwards with a 100kg strenght If it's volume is 100 lt (more or less 25 gallons), according to Archimedes, there is a force of 100lt of water that is pushing him up. What is the force of 100lt of water: exactly 100kg. Given this, inflating the bcd will raise the volume of the diver, that is the pushing up force is larger than the pulling down: the diver go to the surface. Viceversa, deflating the bcd will decrease the volume so the pulling down force is stronger: the diver goes deeper. Now... how come the volume increase when you inflate the bcd: you get the air from the tank and move it to the bcd, so should be the same. The difference is that air is a gas, and gases can be compressed: you can see it using a empty (i.e. full of air) plastic bottle. Even if it is well sealed, you can squeeze it. If you try the same with the bottle full of water, you will see that you can't squeeze it. That is because only gases can be compressed, while liquidsa and solids not. When you compress a gas, you raise its pressure: the higher the pressure, the lower the volume. So what happens: in the tank we have highly compressed air: at least 50 to 200 bars. In the bcd we have low compressed air, usually 10 bars more than the ambient pressure (at 50mt depth, it means that the air pressure is 15 bars). A final consideration: remember that the tank is in metal, not fabric. When you take air out of it it doesn't change its shape (and consequently its volume) , while the bcd, being soft, will change its shape and its volume. Luca |
|||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||
|
|||||||||||||||||||||||||||||||||||||||||||||||||||||
|
10 SIMPLE TIPS TO CONSERVE AIR AND DIVE LONGER
There are very few more frustrating occurrences in scuba diving as having to abort the dive due to lack of air, while everybody else is still having fun down there. Being able to save air as you dive is one of the most important steps to become a good diver. Here are some tips that can help us improve our diving skills
Proper Weighting
Carrying extra weight makes a huge difference on air consumption- you have to inflate your BCD more thus increase drag, and your body's lower part tends to sink down, while upper part rise up- which increases drag furthermoreSimple buoyancy check before diving with a new gear, at a new area, or after along time without diving should do the trick
Buoyancy
Try to achieve and maintain neutral buoyancy as soon as you reach your desired depth. Simple trick is to try hover – breath normally, add minimal amount of air to the BCD, inhale fully to elevate yourself off the bottom and return to normal breathing
Move Slowly
There's hardly ever a need to dive fast- you use up energy and air a lot quicker, and probably scare marine creatures as you do so
Avoid Using Your Arms
Arm muscles are weaker than those in our legs, plus, arms and hands don’t propel us as much as our legs and fins do. Use your hands for signaling, snapping photos rather than swimming
Streamline
Keep all hoses secured, arms tucked, and try to swim as horizontal as possible, thus minimize drag, keep yourself and the equipment off the bottom and avoid damaging the marine environment.
Breathing
Don’t skip a breath. Breathe at the same tempo, long inhalations and exhalations
It's recommended to inhale and exhale as if whistling or sucking air. You can also pick a nice tune to help you breath at the same rhythm
Use Familiar Equipment
To be more relaxed and feel in control, buy your own equipment. You'll also need to make very few changes on estimating weights as mentioned in paragraph 1
Relax
Easy to say, but some newbie diver have a natural fear when diving. The more you dive the more confidence you gain, and the more you realize there's nothing to it
Practice
It all comes down to it. The more you dive the better you get. Consider participating in a Pick Performance Buoyancy Course that fine tunes you buoyancy skills
Dive Shallow
If you still use up air a lot quicker than your buddies, dive slightly shallower, where the air you breathe is less dense and allows you to dive longer
About the Author
PADI, SSI Staff Instructor, a biologist and an Underwater Photographer Find more valuable tips that can help you through picking the right scuba equipment , dive courses , dive destinations , snorkeling and more at http://knows-dive.com