Measurement of Hydrodynamic Coefficients on a Planing Hull Using Forced Roll Oscillations

Abstract

For planing hulls, dynamic lift reduces the submergence of the hull, allowing small motions to result in large changes in hydrodynamic forces and moments. This article explores various modeling assumptions associated with transverse plane dynamics in roll and the hydrodynamic forces in the planing regime. The significance of nonlinearities in the roll hydrodynamic forces for planing hulls was investigated with regard to roll amplitude, model speed, model displacement, and roll oscillation frequency. A wooden 20 deadrise prismatic planing hull was tested at steady roll angles and in dynamic roll at various roll amplitudes and frequencies. Two displacements, three model speeds, three roll amplitudes, and four roll oscillation frequencies were tested. The measured wetted lengths, roll-restoring coefficient, roll-added inertia coefficient, and roll-damping coefficient are presented. The roll-restoring moment is found to be nonlinear with roll amplitude, the added inertia coefficient shows some dependence on model speed, and the roll-damping coefficient shows some amplitude dependence.

A hybrid empirical–analytical model for predicting the roll motion of prismatic planing hulls

“…The roll damping coefficients of the considered cases are computed and displayed in Figure 5. The determined damping coefficient decreases as the Froude beam number increases, which is similar to the experimental results of Judge and Judge 34 and reasonable agreement exhibited between these results. As evident in Figure 5, the predicted values approach the experimental data of light case, as the Froude beam number increases.…”

“…In addition, the predicted values are comparatively close to the measured data by Judge and Judge. 34 The errors in predicting the damping coefficient at this Froude beam number may also be found in the last column of Table 5. The errors are smaller than 13% which implies that accuracy in predicting the damping coefficient by the proposed method for the heavier case is also reasonable.…”

“…The heavier case, however, has significant dependency on the roll amplitude. Since in this article, the ''Results'' section deals with small amplitude (smaller than 10), only the results of the smallest amplitude of Judge and Judge 34 experiments are considered for comparison purposes. The roll damping coefficients of the considered cases are computed and displayed in Figure 5.…”

“…However, Judge 35,36 utilized previous empirical relations by Savitsky 37 and Smiley 38 in order to determine the lift force and heeling moment of a planing boat. Judge and Judge 34 proposed considering the effective deadrise angle for each side of the boat. However, the suggested method by Judge 36 does not consider the effects of port and starboard on each other in the asymmetric condition.…”

Experimental Study of the Wedge Effects on the Performance of a Hard-chine Planing Craft in Calm Water

“…Accordingly, during the last decade, wide ranges of experimental studies have been devoted to study different characteristics of the planing hulls. Performance of these hulls [22][23][24][25][26][27], their seakeeping [28,29], roll motion [30], and even steady yawed [31,32] condition have been studied. The satisfactory, promising, and useful findings of these studies signal that experimental works can be considered as a very reliable alternative methodology for investigating the planing hull characteristics.…”