Low speed course-keeping and changing abilities of the KSUPRAMAX bulk carrier in waves

Abstract

Manoeuvring performances of ships in waves are significantly different from those in calm water. Reliable prediction techniques on the ship’s manoeuvrabilities in actual seas are required at the early design stage. In particular, attentions should be paid to the ship’s course-keeping and changing abilities for its safe operations in rough waves. In this study, course-keeping and zigzag manoeuvres of a ‘KSUPRAMAX (KRISO SUPRAMAX bulk carrier)’ model ship which has a 66,000 DWT supramax bulk carrier hull form are experimentally investigated. The full-scale ship length is 192 m, a 1/64-scaled model ship is constructed for free-running model tests in Ocean Engineering Basin of Korea Research Institute of Ships and Ocean Engineering (KRISO). At first, turning circle tests are repeatedly conducted in long-crested irregular waves with the model propulsion point corresponded to the full-scale design speed of 14.5 knots. Equivalent regular waves that show similar turning circle trajectories and approach speeds of the model ship compared to irregular waves are searched. Next, course-keeping tests are performed in irregular waves and in equivalent regular waves with wave incident angles of 0？180？ at speeds lower than 5 knots. Low speed course-keeping paths, check helms, and drift angles in equivalent regular waves are close to those in irregular waves. 3-DoF modular-type manoeuvring simulation models are constructed based on captive model tests and empirical methods. Since the wave drift forces are equal to sums of hydrodynmaic forces acting on the hull, the propeller, and the rudder during course-keeping manoeuvres, wave drift forces are identified from course-keeping simulations. Zigzag tests are conducted in equvalent regular waves with approaching conditions which are the same as those in course-keeping tests, zigzag behaviors are also simulated by the present models including wave drift forces identified. Course-keeping and changing abilities are discussed with considerations of wave drift forces which are varied with wave incident angles.