How to Calculate the Lift of a Buoyancy Compensator

SCUBA divers must have a lot of skills to dive safely and to enjoy it to its fullest. Determining the lift of the buoyancy compensator (BC) is one of those skills. It allows the diver to calibrate the amount of oxygen she pumps into her BC and the amount of weight she inserts into her weight belt or BC pouches against her own natural buoyancy to achieve neutral buoyancy in open water.

Things You'll Need

  • Buoyancy compensator (BC)
  • Lead BC weights
  • Oxygen tank
  • Fins
  • Diving mask
  • Snorkel
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Instructions

    • 1
      A buoyancy compensator often has pouches to hold extra weight.

      Evaluate your diving environment. Determining the lift of your BC is an environment-dependent function and you must repeat the steps involved with every change in diving environment. For example, the human body is more buoyant in salt water than in fresh water. Simply stated, it is harder to sink in the ocean than it is in the lake. Because of this, you cannot apply your determination of BC lift in the ocean to your determination of lift in fresh water. Neoprene wet suits also add buoyancy to the human body. Diving off the coast of Southern California where the water is cold, for example, is an environment where you are positively buoyant. You are in salt water and you are wearing neoprene, both of which keep you on the surface. Extra weight and less air in your BC is needed to aid your descent. Diving off the coast of Southern Mexico, on the other hand, requires less weight to aid in your descent. You are still in salt water but because the water is much warmer, you do not need to wear neoprene. Finally, fresh water diving in the heat of the summer requires the least amount of weight to descend.

    • 2

      Determine your body's natural buoyancy without wearing any dive gear. Wearing only your swim trunks, enter water that is slightly deeper than you are tall and position yourself vertically. Take and hold a normal breath for 20 to 30 seconds. If you are negatively buoyant, you descend to the bottom while holding your normal breath. If you are positively buoyant, your body remains near the surface. With positive buoyancy, it is more difficult to remain in a still, vertical position. Finally, if you are neutrally buoyant, your still, vertical body hovers in the water while the top of your head remains roughly equal to the water surface. Knowing your natural buoyancy is important, as it impacts the amount of weight needed in your weight belt or BC pouches.

    • 3
      Achieving neutral buoyancy allows you to protect the coral while you enjoy it.

      Don your BC, mask, snorkel and fins. If diving in cool or cold water, don a neoprene wet suit. Enter water that is at least one foot deeper than you are tall and position yourself vertically. Ensure your BC does not have any air in it. As you hover vertically in the water, add weights to your BC. Continue adding weights until you begin to descend. Record the amount of weight that results in your descent. Insert the same amount of weight into your weight belt or your BC pouches each time you dive in the same conditions. Your goal in determining BC lift is achieving neutral buoyancy so that you can both protect and enjoy the marine world all at the same time.