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Figure 6.9 - Semi-submersible platform

Semi-submersibles were introduced initiating from the idea that their wave-

induced motions are decreased by lowering a large part of displacement

(buoyancy) to a region of less wave excitation (fig. 6.10). The requirement for

reduced motions and accelerations of the floating systems is essential because of

the influence of these factors on the process flow in equipment like separation

columns, heat exchangers, etc.

Semi-submersibles are multi-hull column-stabilized structures: an elevated

rectangular platform deck is supported above the water on an array of vertical

columns of minimal water plane area, which are connected to caissons or

longitudinal hulls with interconnecting truss-like structural members below the

water surface. These structures often comprise of two submerged horizontal

pontoons which provide the main buoyancy for the platform but act as catamaran

hulls when moving location at low draft. Typically, four to eight vertical surface

piercing columns are connected to these pontoons. The columns themselves may

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