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www.sname.org/sname/mt July 2013 submergence of the hull, allowing small motions to result in large changes in hydro- dynamic forces and moments. is article explores various modeling assumptions associated with transverse plane dynamics in roll and the hydrodynamic forces in the planing regime. e signicance of nonlin- earities in the roll hydrodynamic forces for planing hulls was investigated with regard to roll amplitude, model speed, model dis- placement, and roll oscillation frequency. A wooden 20° deadrise prismatic plan- ing hull was tested at steady roll angles and in dynamic roll at various roll ampli- tudes and frequencies. Two displacements, three model speeds, three roll amplitudes, and four roll oscillation frequencies were tested. e measured wetted lengths, roll- restoring coefficient, roll-added inertia coecient, and roll-damping coecient are presented. e roll-restoring moment is found to be nonlinear with roll ampli- tude, the added inertia coecient shows some dependence on model speed, and the roll-damping coecient shows some amplitude dependence. Vibration of High-speed Ship Frames BY MICHAEL R. DAVIS, GARY DAVIDSON, TIMOTHY ROBERTS, AND CHRISTOPHER CATO PUBLISHED IN THE AUGUST JOURNAL OF SHIP PRODUCTION AND DESIGN Impact testing of a typical high-speed ship section has shown that the mode of vibra- tion most likely to fall in the frequency range of excitation resulting from propel- ler or rotor blade passing is that where the ship frame rocks in a fore and aft direction about its base connection to the hull plate. is vibration has signicant amplitude to either side of the keel and it is found that connection between the inboard and out- board sides is weak. As a consequence, vibration can occur in two modes in which the opposite sides of the hull either move together or in antiphase. is leads to the structural strain energy in the two modes being slightly different, the mode with rather less strain energy having slightly lower frequency. Because the frequen- cies of the two modes are close together, the transient response exhibits beating in which vibration energy is exchanged between the two sides of the hull at the low beat frequency. Vibration of the ship frames in this manner appears to have been the cause of minor weld cracking where the top of stieners pass through cutouts in the web of the ship frames within the fuel tank areas of the hull. MTGO DEEPER Both the Journal of Ship Production and Design and the Journal of Ship Research are available by subscription. Go to www.sname.org/SNAME/Pubs/Journals1/ and ?nd out why these technical journals are indispensable to naval architects and marine engineers around the world.