Nowadays ships have become gradually larger and larger in size. Accordingly the importance of ship handling in harbor has been emphasized much more than before in order to secure safe navigation and efficient port operation. Ship handling in harbor is carried out mostly at a low speed and is affected by port congestion.
When using tugs, bow or stern thruster, ship’s main engine or rudder during maneuvering in harbor, ship handlers, especially harbor pilots in Korea, think pivot point as if it is the center of all lateral forces acting on ships. The pivot point is traditionally known to be located in about one third of ship’s length from the ship’s bow in the forward movement and in about one fourth from the stern in the backward motion. However the position of pivot point varies depending on external forces such as current, wind, tug etc.
This paper is to find out the accurate meaning of pivot point through several examples and to investigate the right positions of it, not a constant one of one third or one fourth of ship’s length. And the paper also is to suggest the center of lateral resistance of water as that of force couple and to examine how it can be used in harbor maneuvering through some examples.
For the purpose of it firstly, this paper analyzed the positions of pivot point focusing on eighteen(18) cases and investigated the equilibrium of thrust and resistance of water. Secondly, the paper found that the center of lateral resistance of water instead of the equilibrium of lateral forces can be used as force couple and suggested how to find out it. The center of lateral resistance of water is usually determined by the composition thrust and lateral force. Finally, the paper examined examples of application of the center of lateral resistance of water to maneuvering in harbor.
As a result the following were obtained.
(1) The position of pivot point varies depending on forces exerting on a ship, as shown in Table 3.
(2) The equilibrium position of lateral forces varies depending forces exerting on a ship and also can not be estimated easily.
(3) The approximate position of center of lateral resistance of water was suggested instead of The equilibrium position of lateral forces.
(4) By using the couple force of lateral resistance of water and other force such as tug or thruster the turning of a ship can be predicted.
(5) The center of lateral resistance of water can be used in maneuvering in harbor.
However, a lot of experiments are needed to get the center of lateral resistance of water considering key factors. It will be done in the future study.