RIASSUNTO
ABSTRACT
In the structural design of bilge keels, hydrodynamic loads may threaten the structural integrity of both the bilge keel and of the hull itself. In the former case, it is the direct load from differential pressure that causes bending and shear at the root of the bilge keel. In the latter it is the wave bending of the ship hull that is transferred to the bilge keel to cause shear at the connection to the hull. Extreme loads and the sequence over the design life might cause failure, and the likely failure mode that drives design is fatigue, which can be either at the welds on the root of the bilge keel or at the hull itself, the latter caused by the global bending of the ship to the bilge keel. Particular care must be taken on welds and on geometry of the root of the bilge keel at hull. Often large bilge keels extending over large parts of the ship may need to be discontinuous, in order to minimize any risk of potential damage of the hull starting at the weld. In this paper is introduced the role of roll damping in motion analysis including results from dedicated model tests, discussed the hydrodynamic regime and load conditions for the bilge keel under ship motions, presented the approach to calculate the load history under floater motions during the operating life of a ship-shaped unit purposely moored for offshore operations, commented the structural design and recommendations to ensure a safe life for both bilge keels and ship hull, targeting the reduction of roll motions.