Experimental Determination of the Added Inertia and Damping of Planing Boats in Roll.
STEVENS INST OF TECH HOBOKEN NJ DAVIDSON LAB
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This is the third of four reports on research designed to obtain basic hydrodynamic information about planing hulls through the use of captive models tests. The information is to be used for the general study of dynamic stability while underway, course keeping, turning and maneuvering, etc. The models tested were of idealized patrol boats having an LBP of 100 ft., a beam of 20 ft., and a displacement of 100 long tons. The models had prismatic hull forms with 10, 20, and 30 degrees of deadrise. The report presents the results of free oscillation tests on two unappended prismatic hulls of 10 and 20 degrees of deadrise. The tests were conducted at a beam loading coefficient of 0.4375, at three speeds Ov 1.5, 3.0, and 4.0, three trim angles 0, 3, AND 6 DEGREES, and at yaw angles of 0,10, and 15 degrees. Roll extinction records were taken with three different spring stiffnesses, first at rest in air and then underway in water, at each test condition. The roll period and logarithmic decrement were determined from these records and tabulated. The added mass moment of inertia and damping in roll were deduced from these data assuming a linear damped harmonic oscillator. Empirical expressions for the inertia and damping are presented and compared with the data. These expressions are used to predict the rolling characteristics of a prototype 100 ft. boat.
- Marine Engineering
- Fluid Mechanics