McClure and Hove 



to establish these facts was placed on model testing. Towing tests were con- 

 ducted to determine resistance, turning moment, and lateral force in straight- 

 line maneuvers. Also, steering tests were conducted with a self-propelled 

 model. From a qualitative standpoint it was found that the model could easily 

 be steered in a straight path down the model basin using manual remote control. 

 Spiral and zig-zag maneuvers were conducted to determine quantitative direc- 

 tional stability and control as illustrated in Fig. 12. In the zig-zag tests the 

 model was run in a straight path before a predetermined RPM variation was ap- 

 plied causing the vessel to turn. After a specified angle was reached, the RPM 

 variation was reversed. The turns were repeated in both directions and the 

 overshoot and time to complete the cycle were noted. Results show that the 

 platform is about as controllable as a conventional ship hull of the same size. 



One of the measures of controllability is the overshoot angle or the amount 

 the vessel continues to swing in a certain direction after the turning force has 

 changed to the opposite direction. A small overshoot angle signifies good con- 

 trollability. To investigate the sensitivity of the vessel to control changes, 

 small fins or trim tabs were fitted aft of the vertical stern fins. The overshoot 

 angles were 2.5 degrees and slightly greater with the adjustable trim tabs. This 

 does not necessarily mean that the platform is more controllable without the 



1000, 



30 20 10 10 20 

 VARIATION FROM COURSE 

 IN DEGREES 



20 10 10 20 30 



VARIATION FROM COURSE 



IN DEGREES 



Fig. 12 - Time histories of zig-zag 

 maneuvers at 8.0 knots 



428 



