6 Degree of Freedom Motion Analysis of Surface Ship Models

A 6 degree of freedom (DOF) optical motion analysis system has been adapted for the measurement of surface ship model motion. The motions measured by the optical system are surge, sway, heave, roll, pitch, and yaw. Apparently, the calibration of the system is not traceable to a National Metrology Institute (NMI). Measurement results are compared to on-board instruments for the measurement of roll, pitch, and heave, which were calibrated prior to the test. Test results are presented for a Large Medium Speed Roll-on Roll-off (LMSR) ship model with a Transformable Craft (T-Craft) Surface Effect Ship (SES) in tandem connected by a ramp. The LMSR model was attached to a carriage in a rectangular wave-making basin. The results presented in this paper were conducted at a simulated Sea-State 4 and model speed of 0.372 m/s. The results were in reasonable agreement in pitch and roll where the instrument calibration uncertainties were between ±0.19° and ±0.67°, while the manufacturer’s specification is ±1.0°. Heave was measured near the stern by the optical system. The uncertainty in the correction to the center of gravity is estimated to be ±17 mm for the LMSR in comparison to the direct measurement of heave by a string pot at the cg, where the calibration uncertainty was ±1.3 mm.