Wave Drift Forces Estimation for the Preliminary Design of Dynamic Positioning Systems

In present work, a simplified methodology able to provide a sufficiently accurate assessment of wave drift forces is presented, with the aim of providing a procedure which may be applied in the preliminary stages of the design, when the technical data of the ship (such as the hull forms) are not yet available, and only main hull parameters are present. In particular, the 3D panel seakeeping program PRECAL, developed at Cooperative Research Ships (CRS) is utilised. At first, its capabilities are verified comparing numerical results with literature data, showing the code reliability. Then, a series of simplified ellipsoidal hull forms have been analysed and compared with more complex hull forms in order to identify a criterion of equivalence, which may be used when a detailed description of the hullform is not available. Results show that the proposed simplified methodology is reliable and enough accurate to allow a proper sizing of the propulsion and manoeuvring systems of a ship with dynamic positioning requirements in the preliminary stage of the design.