The excess resistance of a ship in rough seas

Article type: Research Article

Authors: Maruo, Hajime

Affiliations: National University of Yokohama, Yokohama, Japan

Abstract: The horsepower of a ship predicted by a tank test is usually the value in a calm sea, but a considerable power should be added to this when a ship is steaming in a seaway. Though the increase of the resistance due to the waves encountered, has been recognized for a long time, there are different opinions as to the cause of the excess resistance. In 1939, Dr. Kreitner [1] suggested that the additional resistance is mainly due to the reflection of sea waves, but Sir Thomas H. Havelock [2] did not agree with him, showing the drifting force due to wave reflection to be very small. In 1942, Havelock [3] proposed a theory in which the additional resistance arose from the phase difference between the ship’s motion and the excitation of the wave. Some computations were carried out by Mr. M. St. Denis, according to Havelock’s theory [4]. From the theoretical point of view, however, this method is only an approximate or tentative one. Some years ago, Mr. Hanaoka [5] gave a theory of the wave resistance of a ship which is forced to oscillate, and he showed a considerable increase of the wave resistance due to forced heaving and pitching. He also applied the theory to the resistance experienced by a ship among waves making the approximation that the effect of the seaway was expressed by the wavy motion of the ship’s surface relative to still water [6]. The additional resistance obtained by Hanaoka is different from Havelock’s findings. There seem, then, to be at least two independent components in the additional resistance. Unfortunately, however, we have not found any reasonable connection between them, because Hanaoka’s theory was originally based upon the motion of a ship in still water instead of the actual seaway. The difficulty lies in the fact that the additional wave resistance appears in the higher order quantity which is usually omitted in the linearized theory, but if we examine carefully the terms which should be omitted and those which should be taken into account, we can still make use of the linearized theory in solving the problem of the excess resistance of a ship in rough seas. In this paper, the author will propose a general theory of the force experienced by a ship oscillating amongst waves, and then he will attempt a computation of the motion of a ship of simple shape in head seas, from which the resistance increase will be evaluated.

DOI: 10.3233/ISP-1957-43501

Journal: International Shipbuilding Progress, vol. 4, no. 35, pp. 337-345, 1957