When a ship is rolling in waves with so large mean heel angle that her deck edge is immersed, characteristics of rolling motion, for example the resisting moment, are very much different from those in rolling about an upright condition. Shipping of a large quantity of sea water brings about instantaneous heeling over 30 degress occasionally and some ships capsize and the others come upright gradually. The author arranges in this paper some interesting experimental results in relation to above mentioned phenomena, unsymmetrical rolling, and example of the calculation of resistive moment and forces due to wave-making is tabulated for the sake of qualitative appreciation. In the next place, experimental results on unsymmetrical rolling of two ship models, a fishing boat and a cargo ship, are presented. In the fisher-boat experiment, observation of unsymmetrical rolling due to shipping water in regular waves was the main subject, while, in the cargo ship experiment, the wave characteristics were kept constant and the wind velocity was changed from 0 to 8 meters per second so as to obtain the information on the combined action of wind and waves. Unsymmetrical rolling due to shipping water with weather-side heel took place under wave action alone when the freeboard was too small and/or the effective area of freeing port was insufficient. It is noticeable that the principle of superposition seems to fail sometimes as to motions of ships under combined action of wind and waves. In other words, these experiments revealed that the rolling amplitude varied with increasing wind speed, the heel angle due to the same wind velocity increased more or less under the additive action of waves and the velocity of drifting was independent of the existence of waves except in case of very low wind speed.

  • Corporate Authors:

    Society of Naval Architects of Japan

    23 Shiba-kotohiracho, Minato-ku
    Tokyo 135,   Japan 
  • Authors:
    • Tamiya, S
  • Publication Date: 1970

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Filing Info

  • Accession Number: 00035131
  • Record Type: Publication
  • Source Agency: Society of Naval Architects of Japan
  • Files: TRIS
  • Created Date: Oct 27 1972 12:00AM