cylinder specification tables).

Steel cylinders are typically very negative, and will remain negative even when the air inside has been consumed.  In contrast, aluminum cylinders are less negatively buoyant.  They are typically negatively buoyant at the beginning of the dive, due to weight of the gas they contain.  As that gas is consumed, they can become positively buoyant.

In most instances, a typical AL80 cylinder (aluminum cylinder commonly used by dive centres for rental) requires 2kg of weight to off-set cylinder buoyancy at the end of the dive, when reserve air capacities are reached (50bar/500psi).

ASSESSING YOUR SCUBA BUOYANCY SKILLS

Depending on a person’s level of diving experience, there is a set of basic assessments that will enable a developing diver to evaluate their proficiency in scuba buoyancy control.  As you gain experience and complete more scuba dives, assess yourself against the following criteria to identify where you can improve your scuba buoyancy control.

A.        Novice Diver

•   Perform a controlled descent to depth, stopping and hovering within 3m/10ft of the bottom

•  Hover for one minute in a horizontal position whilst remaining within 1.5m/5ft of the starting depth

•  During dives, stop at will and hover horizontally at a constant depth, without adding/subtracting air to/from the BCD and without sculling or fining.

B.        Intermediate Diver

•  Demonstrate controlled descent to depth, stopping within 5’(1.5m) of the bottom.

•  Demonstrate buoyancy control and propulsion during the dive, without use of hands.

•  Hover for 2 minutes in a slightly head down position whilst remaining within 2’ (60cm) of the start depth

•  While floating horizontally, perform an air-sharing drill without changing depth more than 5’ (1.5m)

C.        Advanced  / Technical Diver (wearing full equipment and stage bottles)

•  Demonstrate controlled descent to depth, stopping within 30cm/1ft from the bottom

•  Perform all buoyancy control or propulsion without use of the hands.

•  Hover for 2 minutes in a slightly head down position whilst remaining within 15cm/6” of the bottom

•  Hover in mid-water for 2 mins in a slightly head down position, remaining within 30cm/1’ of the start depth

•  Whilst hovering horizontally perform a full air-sharing drill without changing depth more than 60cm/2ft


 

Next article: ‘Assessing Your Weight Requirements’

Previous Articles:

Scuba Buoyancy Masterclass 1of9 – Buoyancy Control for Scuba Divers

Scuba Buoyancy Masterclass 2of9 – The Need for Buoyancy Control

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