Investigation into Ship Maneuverability in Shallow Water by Free-Running Model Tests

Abstract

This study concerns the effects of water depth and ship speed on the maneuverability of ships. Free-running experiments were conducted to determine the coefficients and the nonlinear term in Nomoto's expression for the turning rate of a maneuvering ship. The nonlinear term which represents the steady turning characteristic of the ship is determined by the spiral and reversed spiral tests, while the time constants in Nomoto's expression are obtained from the zigzag maneuvers. &&The experiments were co_ducted on an 8 ft model of the supertanker Tokyo Maru at five different water depths of 1.2, 1.5, 2, 3 and 8.7 times the draft. For each water depth, results were obtained at three different speeds of the model. &&The results indicate that the course stability of the ship is strongly dependent on the water depth. In particular, the stability decreases as the water depth decreases and it reaches a minimum at a ratio of water depth to draft between 1.5 and 2, then it starts to improve as the water becomes shallower. These findings are in agreement with earlier results obtained by Fujino (1968) using the Captive Model Test technique for the same ship. &&The present results also show that the effect of speed on the maneuverability in shallow water is more pronounced at the low speed limit.