The Technical University of Nova Scotia, Halifax, Nova Scotia has a small ship-model towing tank located in the Civil Engineering Hydraulic Laboratory, currently being used by the Ship Hydrodynamics Research Group.The dimension of the tank is lm x lm x 30m. A carriage is driven by a 1/4 horsepower constant torque DC motor. It can reach a maximum velocity of 2.44 m/s (8 ft/s) and sustain a maximum model resistance of 9.1 kgs (20 lbs). The motor control unit permits the carriage to be run in both forward and reverse directions at the same speed with a maximum acceleration or deceleration of 1.22 m/s^2 (4 ft/s^2) as shown in Fig. 1.

A precisely computer-controlled wave-making system has been purchased from Edinburgh Design Ltd., U.K. and recently installed in the tank. It has two wave-makers, one at each end. Either one can act as a wave-maker or a wave-absorber (Figs. 2 and 3). The system can make progressive waves or standing waves, as well as regular waves or irregular waves. The maximum wave height is about 0.3 m (1 ft) and the frequency range for sinusoidal wave generation is from 0.2 hz to 2 hz.

A motion measurement device was developed in-house for the two-degree of freedom of motions. In particular, heave and pitch displacements could be measured simultaneously. It consisted of a LVDT (linear variable differential transformer) and a RVDT (rotational variable differential transformer) of 10% linearity. The LVDT was mounted on the carriage just above the model and the RVDT was attached directly at the base of the heave staff. The model was attached to one end of the heave staff by a connecting device. This device was designed in a way such that only one rotational motion, pitch was permitted. The heave staff was made of a square aluminum rod and guided by eight high-precision roller bearings housed in a PVC block. This rod, in tum, allowed the model to move in heave only. Except heave assembly is shown in the schematic arrangement (Fig. 4) and Fig. 5.

The hull form chosen for this seakeeping test was a SWATH 4A hull with the sectional area curve and the waterplane curve shown in Fig. 6 [l). The model used in the present study was constructed of balsa wood to a scale factor of 1:153 (Fig. 7). A list of principal particulars is given in Table 1. The model was ballasted to the design waterline. Longitudinal CG was measured by weighing the model on a weighing scale, vertical CG was measured through an inclining experiment, and the radius of gyration was determined by swinging the model in pitch with the pivotal method.

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