A practical method for computing the sinkage and trim experienced by a ship that advances at constant speed through calm water of large depth and lateral extent is considered. This method is based on a slender-ship approximation that defines the flow about a ship explicitly in terms of the ship speed and hull shape. Thus, the method is particularly simple, robust, and efficient. In spite of its simplicity, the method yields predictions of sinkage and trim in reasonable agreement with experimental measurements.
The sinkage and trim experienced by a ship that advances at constant speed through calm water of large depth and lateral extent is considered. A large number of well-established alternative methods for computing steady free-surface flow about a ship have been developed. These methods include semi-analytical theories based on various approximations (thin-ship, slender-ship, 2D+t theories), potential-flow panel (boundary integral equation) methods that rely on the use of a Green function (elementary Rankine source, or Havelock source that satisfies the radiation condition and the Michell linearized free-surface boundary condition), and CFD methods that solve the Euler or RANS equations. These alternative calculation methods are reported in a huge body of literature, not reviewed here. Every one of these alternative calculation methods can be used to predict the sinkage and trim experienced by a ship; e.g. Subramani et al. (2000), Yang and Löhner (2002). Many practical applications require very quick assessment of numerous alternative designs, as is typically considered during preliminary and early design stages. For such practical applications, and for hydrodynamic hull-form optimization, a simple approximate calculation method that is easy and fast to implement, very robust, and highly efficient is useful, if not necessary. Such a method is presented in this study. The method is based on the slender-ship flow approximation and the simple free-surface Green function given in Noblesse (1983) and Yang et al. (2004).
