Development and validation of a small-scale planar motion mechanism (PMM)

This work presents a multi-scale evaluation of captive maneuvering experiments conducted using two Planar Motion Mechanisms (PMMs) at the U.S. Naval Academy: the long-established large PMM in the 116 m (380-ft) towing tank and a newly developed small-scale PMM designed for the 37 m (120-ft) facility. The large PMM has generated maneuvering hydrodynamic derivatives for more than three decades and serves as the benchmark for assessing the performance of the compact PMM. To examine scale effects and validate the new system, two symmetrically scaled models of a frigate hull form were tested on both PMMs at full-scale equivalent speeds of 15 and 20 knots. The resulting sway-, yaw-, and rudder-dependent derivatives were extracted through standard static and dynamic PMM procedures and compared across scales. The data show excellent agreement between the two systems, with nearly overlapping regression slopes and small 95% confidence intervals for all derivatives. These results confirm that the small PMM reliably captures the dominant maneuvering physics despite operating at significantly lower Reynolds numbers and reduced force amplitudes. The validated small-scale PMM offers a low-cost, high-accessibility alternative for maneuvering research and education, providing high-quality hydrodynamic derivative data in facilities where full-scale PMM installations are impractical.