Ship system can be divided into four sub-systems: hull, propeller, main engine and operation system which severely affect the characteristics of a ship. In determining ship speed in waves, two factors are considered the involuntary speed loss due to added resistance caused by wind and waves, and the voluntary speed loss by command of operation system to prevent severe ship motions. In this paper, the main function of four sub-system is analyzed for input/output relations and propulsive coefficient and a useful method to predict involuntary speed loss of a ship is presented. Two calculated examples for a high speed container ship and a passenger ship with single screw and diesel engine are given.

This paper presented a method of evaluating navigational safety of a ship by means fo the integrted seakeeping performance index(ISPI). The ISPI is defined by measuring only any one factor through the medium of relative dangerousness of the other factors for evaluating seakeeping performance. This evaluation method can be applied to the ships for any types and loading conditions. In devloping the practical evaluation system of navigational safety, it is expected to be useful to solve the difficulties in measuring factors by sensors. The results are also useful for devloping the optimum type of ship by applying at the initial design phase.

Several factors can be chosen for evaluating seakeeping performance, such as deck wetness, propeller racing, slamming, rolling, vertical acceleration and vertical bending moment, in consi-deration of the safety of human being, cargo and ship. In fact, there are few developments for an evalua-tion method of seakeepting performance correponding with each ship's characteristics. The purpose of this paper is to develop an quantitative evaluation method of seakeeping performance according to ship types. The scope and the method of this study are as follow. (1) Obtain each response amplitude of ship's motion in waves by Ordinary Strip Method and apply it to short-crested, irregular wave for random process of the factors on seakeeping performance. (2) Define the evaluation index, the dangerousness, the maximum dangerousness and the evaluation diagram. (3) Figure out the different characteristics according to ship types by computer simulation of evaluating seakeeping performance. (4) Adopt vertical acceleration and one of rolling or lateral acceleration as the factors on seakeeping performance by clarifying the correlation of stochastic process. This study developed an evaluation method coincident with each ship's characteristics, and suggested a device for application to actual ship. This method might be useful in developing the practical system of seakeeping performance in accordance with ship types. The ship models for computer simulation are 175m container ship types, 93m tranning ship HANARA as passenger ship type, 259m bulk-carrier type and 164m pure car-carrier type.

Officers and ratings as a group might show differences in some aspects of personality , human relations, job attitudes, perception of business environment and surrounding organizational structure. It has been traditionally believed that licenced-officers are required to have nicely-paired leadership and dignity , and ratings obedience in maritime field. This survey revealed that officers and ratings have some differences in the actual behavior, knowledge , understanding attitude etc., In summary , officers as a superstructure of merchant ship's orgnaization are different, to some degree, from ratings as an infrastructure in several aspects. Officers are believed to have the characteristics of maturity by taking concern of business environment , social circumstance away from the vessels which they are on board. In contrast, ratings are greatly interested in the surrounding environment associated with themselves, and also experiencing alienation and technology.

The recently-developed automated vessels require a system which evaluates the operating conditions of the ship at present position from weather information as well as sensors ; forecasting the operations condition in the state to come in foreseeable future ; and suggests the optimum course and speed for ship's safety. According to a study, deck wetness, propeller racing, slamming. rolling, vertical acceleration, lateral acceleration, vertical bending moment at midship etc. were chosen as the factors for evaluating seakeeping performance. As a matter of act, there is no developing the hardware of a system which could consider all the factors on seakeeping performance. This study introduces a theoretical method which makes it possible to evaluate the seakeeping performance by applying a theory from reliability engineering, and thereby establishing a safety space. The author adopts rolling and pitching as the factors on seakeeping performance by clarifying the correlation of stochastic processes the factors presently adopted for evaluation system in consideration of the safety of human being, cargoes and the ship. This method of evaluation shall be of much use in developing the practical system of seakeeping performance of a ship in waves.