Instructor Manual
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Ocean Diver
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Adapting to the underwater world
Copyright © BSAC 2017
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Positive buoyancy
• Too light
• Physically tiring
Positive buoyancy makes you too light and the ensuing struggle to remain
below the water is physically tiring.
• Uncontrolled upward movement
More importantly, being too light risks an uncontrolled ascent and possible over-
expansion of the lungs as ambient pressure reduces quickly.
Negative buoyancy
• Too heavy
Negative buoyancy makes you too heavy and is also physically tiring
• Physically tiring
Negative buoyancy makes you too heavy and the ensuing struggle to remain
above the seabed or at the planned depth for your dive are physically tiring
• Risk of going too deep
There is a risk of descending below safe diving depths.
• Damage to self or marine life
Bouncing off the seabed can damage marine life and the diver’s equipment.
• Sinking if on surface
Being too heavy might make it harder to stay securely at the surface.
Buoyancy in practice
A diver with no equipment will float on the surface. Each
piece of added diving equipment has a weight and a
volume, some will increase the diver’s buoyancy and
others will decrease it.
Descent
• Diving suits + scuba kit normally cause positive buoyancy at the surface
The combined effect of the diver’s body, their suit and scuba equipment will
normally result in positive buoyancy.
• Add weight to achieve neutral buoyancy
This buoyancy is compensated for by adding weight to a weight system to allow
the diver to descend.
