An investigation into the course stability of the B.S.R.A. 0.85 block coefficient methodical series form

The report describes experiments carried out on the rotating-arm facility at the Admiralty Experiment Works, Haslar, to investigate the course stability of the B.S.R.A. 0.85 C_B form. The fibreglass model, which was fitted with a propeller, was attached to the arm in such a way that it was free to heave, pitch, and roll, but constrained in the surge, sway, and yaw modes.

The forces and moments acting on the model were measured with the model set at 48 and 80 ft radii. The side-slip angle was varied from minus 8 deg to plus 8 deg in steps of 2 deg at each radius.

The results are plotted as non-dimensional side force against side-slip angle and non-dimensional yaw rate. Computed values of steady-state yaw rate have been plotted against rudder angle for different values of rudder derivative.

On the basis of the experiments carried out it is concluded that this form would be directionally unstable with the area of rudder fitted for these tests, but attention is drawn to the fact that the degree of instability is no worse than that present in a number of large tankers already in service.