# CALCULATIONS ON THE STEERED MOTION OF A SHIP UNDER THE ACTION OF EXTERNAL FORCES - PART 2

The author showed in the former report a method of calculating the steered motion of a ship under the action of external forces such as wind and/or flow. In such calculation, since the propeller experienced very wide range of loads and accordingly the rudder relative speed varied much, it seemed to be necessary to express the propeller and rudder forces separately from the hull forces. Including the above requirement, the author proposed here a new mathematical model for such practical calculation of steered motion, and applied it to the analysis of self- propelled model test data in the rotating-arm tank at Ship Research Institute. The propeller force was described as the function of advance speed, and a mean effective rudder speed was assumed to be a geometrically composed function of propeller revolution and wake. An effective attack angle of the rudder including the above rudder speed and hull-interaction coefficient was applied, which has been decided from the analysis of total longitudinal forces as a function of drift angle, turning rate and rudder angle. A method of analyzing the rudder force derivatives was attempted with relation to both the measured side force and moment at the same time by a last-squares method, taking the rudder moment upon ship into account. From the analysis of the new mathematical model applied to an ocean- going car ferry model tested in the rotating-arm tank, the following conclusions were obtained: 1. Hull and rudder derivatives could be derived separately from a self- propelled restrained model ship. 2. Accordingly an arbitrary propulsion point of the model ship could be chosen. 3. The effect of interaction between hull, propeller and rudder, besides the well-known propulsion factors, could be approximated in the form of effective rudder angle, including two simple coefficients which represent the effect of hull and propeller upon rudder.

• Supplemental Notes:
• Selected paper from the Journal of the Society of Naval Architects of Japan, Vol. 134, December 1973.
• Corporate Authors:

Society of Naval Architects of Japan

23 Shiba-kotohiracho, Minato-ku
Tokyo 135,   Japan
• Authors:
• Ogawa, Atsushi
• Publication Date: 1974

## Filing Info

• Accession Number: 00097596
• Record Type: Publication
• Source Agency: Society of Naval Architects of Japan
• Files: TRIS
• Created Date: Jul 29 1975 12:00AM