Semi-Captive Model Test Technique to Identify Maneuvering Characteristics of Ships

Abstract

Semi-captive model test technique, which is possible by means of quite simple equipments and measurement in a towing tank, to identify the maneuvering characteristics of ships is proposed. Using a container ship model, an experiment is carried out in the No.3 Experimental Tank of SRI, and methods of experiment and analysis are examined. A self-running ship model is captured by a towing block set on a towing carriage of the tank. Surge, sway and roll motions are constrained, and surge force and sway force are measured by a force gage on the ship model. The towing block has a vertical rod, around which yawing motion of the ship model is free, and the yawing is measured by a potentiometer. Heave and pitch are also free but not measured. During the model is running in the towing tank, ship motion is induced as a response to the steering of the rudder. Propeller thrust, rudder angle and normal force on the rudder are also measured and recorded. Analysing these measured data, coefficients of equations of maneuvering motion of the ship model are identified. Several methods of analysis are examined. In combination with oblique towing test and rudder angle test, sinusoidal steering test with the semi-captive test device gives rotatory derivatives. Therefore a role of PMM test can be played by this newly proposed experimental technique. More precise measurements by further improved device and comparision of the resulsdts with those of the free-running model test or captive model test are expected to confirm the validity of the method and utility for practical ship design.