Prediction of Steering and Manoeuvring of Ships 



performed with 6 or 7 metre models without encountering serious blockage ef- 

 fects. When designing the planar-motion mechanism it was considered impor- 

 tant that the large, accurate, wax models used for resistance and propulsion 

 work should also be used for planar-motion mechanism tests. This enabled the 

 wide experience available regarding these models to be utilized and was also 

 advantageous from an economic point of view. The conventional wax models 

 have been found to be sufficiently robust when reinforced by two transverse 

 wooden bulkheads and one or two laminates of glass-fibre on the inside surface 

 (see Fig. 7). 



Fig. 7 - The HyA planar-motion mechanism shown 

 suspended over a 6-m (ZO-ft) wax model for pho- 

 tographic purposes 



In order to obtain acceleration and damping of the same order of magnitude, 

 and to reduce the likelihood of frequency problems while still enabling sizeable 

 yaw velocities to be generated, the HyA planar-motion mechanism was designed 

 for lower frequencies and larger amplitudes of oscillation than the mechanism of 

 Gertler (6) and Goodman (7). This proved to be a fortunate decision, as frequency 

 problems caused by reflection of surface waves from the tank walls arose at 

 lower frequencies than expected. 



A general impression of the layout of the mechanism is given in Figs. 7 and 

 8. It is contained in a flat frame of welded angle sections which is in itself flex- 

 ible in torsion but very stiff when in use, by virtue of being solidly clamped to 

 the strong working-section of the carriage. 



The solid main shaft is driven via a 1:50 Moss worm-and- wheel reduction 

 gearbox and a 1:2 Power-Grip "timing" belt drive by a 2-1/2-hp Thrige syn- 

 chronous electric motor. 



329 



