Patent ID: 7117810
Filing Date: 2006-10-10
Classification: B63B

Abstract:
1. A floating platform ( 1 ) for offshore drilling or production of hydrocarbons, comprising a topsides ( 2 ) equipped with drilling and/or production equipment, and a substructure ( 3 ) comprising a lower pontoon ( 4 ) and columns ( 5 ) connecting the pontoon ( 4 ) to the topsides ( 2 ), where the platform ( 1 ), when in service, is subjected to wave forces which cause heave motion (s1, s2) and roll and pitch motion (p 1 , p 2 ) of the platform ( 1 ) in the sea ( 7 ), where a heave motion (s1, s2) of the platform ( 1 ) causes a vertical displacement of the platform's center of buoyancy (B) which in turn causes a change in the metacentric height (GM) of the platform, that the columns ( 5 ) in portions ( 6 ) which are moved through the waterline ( 8 ) during the motion of the platform ( 1 ) in the sea ( 7 ) are so adapted that the moment of area inertia with respect to a central axis ( 9 ) of the columns decreases as the distance from the pontoon ( 4 ) increases, so that the moment of area inertia of the waterline area of the columns decreases upon downward heave motion (s 1 ) and increases on upward heave motion (s 2 ), wherein the columns ( 5 ) are so adapted that the change in the moment of area inertia of the waterline area on heave motion (s 1 , s 2 ) essentially compensates for the change in the metacentric height (GM) as a consequence of the displacement of the centre of buoyancy (B) of the platform, by the platform designed in accordance with the criteria where GM, the metacentric height, is the distance between the centre of gravity and the metacenter, KG is the distance between the midpoint of the keel and the centre of gravity, KB is the distance between the midpoint of the keel and the centre of buoyancy and BM is the distance between the centre of buoyancy and the metacenter, where the platform has a draught T, which on heave motion increases by +/−δT, and where to minimize or eliminate the effect of the heave motion on the roll and pitch motion, δGM(δT) must be equal or close to zero, which gives that wherein the columns (