ABSTRACT This paper describes a computer program which calculates the three translator motions heave, surge and sway - and the three rotary motions - roll, pitch and yaw - of a ship, represented by a rectangular block, moored in regular waves of given height and period approaching from an arbitrary direction. Accelerations, velocities and displacements and the forces in up to 30 non-linear mooring lines or breasting dolphins are printed out at successive small time intervals during passage of the waves, using first order linear wave theory and the Froude-Krylov hypothesis. The ship is represented as a rectangular block of equivalent displacement and is partitioned into a number of elements by equally-spaced planes parallel to its length, width and height dimensions. The Froude-Krylov hypothesis and the Airy Theory are used to calculate inertia, pressure and drag forces. The six degrees of freedom of the floating rigid body are represented by a system of six equations of motion which take into account all the forces acting on the body at a given instant, including hydrodynamic forces, forces in the moorings and external forces due to tornado, wind or current. A solution for the simultaneous accelerations in the six degrees of freedom is obtained by Newmark's "beta" method, from which velocities, displacements and mooring forces follow directly. The latest set of mooring forces is used to recalculate the accelerations until convergence is obtained to a predetermined tolerance, usually after only a few cycles. INTRODUCTION From the time man first went to sea in ships, naval architects have been concerned with the motions of a ship in a seaway. Their concern stemmed from considerations of safety of the vessel and its cargo, speed, passenger comfort and economy of propulsive power. Only relatively recently has the civil engineer become interested in the problem of ship motions. His concern was aroused by the need to locate ship berths in ever increasing water depth which brought with it increased exposure to ocean. waves. Although the design of mooring facilities tends to be governed by berthing impacts, exposed locations require that the designer also examine the forces on the ship and on the mooring structures induced by waves which may arrive while the ship is still moored at its berth rather than underway in the relative safety of the open sea. The interaction between the flow of water around a floating body and the motions of that body is so complex that in the past greater reliance had to be placed on model tests rather than on mathematical analysis. While confirming model tests will continue to be required, the mathematics for the solution of the ship motion and mooring forces problem has made sufficient progress to provide a reasonable basis for the design or mooring facilities. Wilson (1959) showed that a fairly accurate solution for ship motions in a monochromatic head or beam sea could be obtained by making assumptions which simplify the problem considerably.