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One Star Diver (ISO)

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  1. Welcome to the Underwater World
    5 Tópicos
  2. Diving Equipments
    6 Tópicos
  3. Our First Contact with Water
    9 Tópicos
  4. The Effects of Changes in Pressure
    4 Tópicos
  5. Breathing with Scuba Set
    10 Tópicos
  6. Limitations of Breathing Air Underwater
    3 Tópicos
  7. Planing and Monitoring Your Dives
    6 Tópicos
  8. After the Dive
    5 Tópicos
  9. About the Practical Skills
    12 Tópicos
  10. Underwater Wildlife
Módulo 3, Tópico 5
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When we start the descent and breathe on the regulator, we notice that maintaining neutral buoyancy is not so easy. As we will see in the next chapter, changes in pressure affect the volume of the suit and the vest or BCD, causing the buoyant force we experience to be variable. To maintain neutral buoyancy, we must change the volume we take up in the water by inflating or deflating the BCD.

The weight belt, with the minimum amount of weights needed and well placed, should allow the diver to have negative buoyancy and to descend. Then, aided by the volume of the BCD, the diver will be able to be neutrally buoyant at any depth. Divers can remain neutral for a long time, without having to make any effort with their arms or legs, thus, reducing their fatigue and air consumption. Neutral buoyancy allows us to move with our body horizontally rather than oblique. This position offers less resistance in

the water, making finning more effective and does not lift sand from the bottom or hurt sea creatures living there.

Moreover, BCDs significantly increase safety at the surface as they can be used as a life jacket. If, due to an emergency we need to float higher in the water, this can be achieved by inflating the BCD to full capacity.

Types of BCDs

BCDs consist of:

  • A bladder where the air is stored
  • An inflator hose through which air can go in and out, whether it is blown by the diver or comes from the cylinder through the automatic inflation system
  • Dump valves
  • A fastening systemint

The differences between BCDs are marked by the blad- der’s position and the way it is held.

The most commonly used model is the one that we call a jacket. It has a plastic piece on the back (backpack) that secures the cylinder with one or more straps. That way diver’s coupling with the cylinder is quite comfortable.

The distribution of air on the diver’s sides, surrounding his/her centre of gravity and close to the weight belt, facilitates keeping the diver’s body horizontal. Also, when inflated on the surface, this brings the diver’s body out of the water.

“Wing”-style BCDs

These consist of a steel or aluminium plate attached to the diver’s body by a harness, acting as a backpack. On the other side, it holds the cylinder.
The plates can vary in weight, but their shape and screw holes are standardized.
The “wing” is placed between the plate and the cylinder. It is inflated or deflated by using an inflator hose and valves identical to those of a jacket. It is usually disc-shaped (colloquially called a donut) and its advantages are:

  1. It is more hydrodynamic as it doesn’t have the pockets found on a jacket (it has less surface in contact with the water and therefore offers less resistance).
  2. The heavy plate allows you to remove some weights from the belt.
  3. It facilitates horizontal body position by weighing divers down on their back, close to their centre of gravity.
  4. It is modular: plate, wing, and harness can be purchased separately.
  5. It adapts to people of all sizes, just adjust the harness strap as with backpacks.

If you wear a wing-style BCD for the first time, you must:

  1. Know the weight of the plate so that you remove weight from the weight belt accordingly.
  2. Before use, adjust the harness straps so that they fit properly.
  3. Secure the cylinder to the wing/plate/harness with the help of someone who knows the system well, to be sure everything is firmly fastened.