A method of launching an elongate subsea structure such as a pipeline bundle unit into water comprises providing buoyant support to the structure by displacing water with a hollow buoyancy unit that applies buoyant upthrust to the structure. By lowering the buoyancy unit in the water to bring a permanently open aperture of the buoyancy unit beneath a surface level of the water, the buoyancy unit is flooded with water through the or each permanently open aperture to reduce the buoyant upthrust applied to the structure.
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