Lobzilla
Contributor
Excellent article that will be helpful for many struggling with the basic concepts of buoyancy control. This has potential for a sticky.
A minor suggestion for editing:
1) A BCD is primarily a buoyancy COMPENSATOR. The controller is our brain. We use a BCD to compensate for compression of our exposure protection at depth and to compensate for the loss of weight due to gas consumption. We use the BCD to "set" a target depth around which we can ascend or descend with breathing CONTROL.
Some suggestions for part 2 of the series:
1) Bouyancy is an unstable equilibrium in the presence of compressible volume. Once we go outside the depth window that we can control with our lungs, the ascent or descent will run away. At this point our buoyancy controller (the brain) has to send signals to our feet or hands. If we have fully exhaled and are still ascending we need to either use our fins to kick down, vent gas out of the BCD (and/or drysuit) or grab something fixed in the water column otherwise we WILL end up on the surface. We should not be afraid to use other means of staying where we want to be when our lungs run out of control. (The extreme case is diving a rebreather where our lung displacement is completely cancelled out by counterlungs (i.e. bags) we breathe in and out of; there we have to become very skilled with fine-tuning our BCD volume.)
2) The size of the depth window that we can control purely with breathing depends on the amount of compressible volume we have on us. The thicker the neoprene, the more will our displacement (volume) change with pressure and the smaller will the lung-controllable depth window be. Similarly, being over-weighted requires more gas in the BCD to compensate(!) for that unneeded weight. More gas in the BCD means more compressible volume and a smaller depth window that we can control with breathing.
A minor suggestion for editing:
1) A BCD is primarily a buoyancy COMPENSATOR. The controller is our brain. We use a BCD to compensate for compression of our exposure protection at depth and to compensate for the loss of weight due to gas consumption. We use the BCD to "set" a target depth around which we can ascend or descend with breathing CONTROL.
Some suggestions for part 2 of the series:
1) Bouyancy is an unstable equilibrium in the presence of compressible volume. Once we go outside the depth window that we can control with our lungs, the ascent or descent will run away. At this point our buoyancy controller (the brain) has to send signals to our feet or hands. If we have fully exhaled and are still ascending we need to either use our fins to kick down, vent gas out of the BCD (and/or drysuit) or grab something fixed in the water column otherwise we WILL end up on the surface. We should not be afraid to use other means of staying where we want to be when our lungs run out of control. (The extreme case is diving a rebreather where our lung displacement is completely cancelled out by counterlungs (i.e. bags) we breathe in and out of; there we have to become very skilled with fine-tuning our BCD volume.)
2) The size of the depth window that we can control purely with breathing depends on the amount of compressible volume we have on us. The thicker the neoprene, the more will our displacement (volume) change with pressure and the smaller will the lung-controllable depth window be. Similarly, being over-weighted requires more gas in the BCD to compensate(!) for that unneeded weight. More gas in the BCD means more compressible volume and a smaller depth window that we can control with breathing.
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