| Abstract | Model experiments were carried out for the Department of National Defence in the towing tank of the National Research Council in St. John’s to investigate seakeeping interaction in head seas and following seas of a corvette and rigid-hull inflatable boat (RHIB) operating alongside the corvette at midships with 1.5 m lateral gap, at forward speed of 8 knots.
Models of scale 1:11.625 were used for these tests. The corvette model was towed by the carriage and free to heave, pitch and roll. The RHIB model was self-propelled, with speed and heading controlled by an autopilot system. The models were tested both side by side and alone at a forward speed of 8 knots, and the RHIB was also tested alone at a forward speed of 4 knots to examine the effect of speed on seakeeping.
The wave conditions included regular waves of 1/50 steepness at 14 full-scale wave frequencies ranging from 0.7 to 2.0 rad/s full-scale, and an irregular seastate defined by a Bretschneider spectrum with significant height of 1.25 m and peak wave period of 7.5 s full-scale.
Heave, pitch and roll motions of the corvette were measured, and motion displacements of the RHIB were measured in all six degrees of freedom, along with the propeller shaft speed and steering angle.
Comparison of the motions of the vessels in the different test configurations showed that the RHIB expectedly had little effect on the corvette motions, while the motions of the RHIB were affected significantly by the proximity of the corvette. In particular, roll and yaw motions were increased, as the corvette generated lateral wave action for the RHIB. On the other hand, in following seas surge, heave and pitch motions of the RHIB were attenuated by the presence of the corvette. Trends observed in irregular seas were consistent with those observed in regular waves. The effect of speed on seakeeping of the RHIB alone was quantified. A large set of experimental data was provided for validation of the numerical tool for prediction of seakeeping interaction. |
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