Sea-trial verification of air-filled rubber membrane for mitigation of propeller cavitation induced hull excitation

• Full-scale measurement with air-balloon has recorded 65% reduction of hull-vibration.
• Inflation method for the balloon is presented by a use of the ideal gas law.
• The simple device is expected as an inexpensive alternative for the propeller cavitation related vibration issue.

At a certain frequency, an air-bubble excited by an acoustic wave produces a destructive interference, which plays a vital role in mitigating propeller cavitation induced pressure fluctuations on ship׳s hulls. By taking advantage of the acoustically transparent nature of rubber material, previous effort proposed employing an inflatable air-balloon so that the destructive interference could be implemented without any energy consumption. For its verification in a full-scale ship, this paper presents sea-trial measurements with the following major contribution. To inflate the balloon to the design size, and to keep the volume constant despite draught changes, a parametric relation is proposed by a semi-analytical method incorporated with the ideal gas law. This scheme is exploited in the full-scale measurements to attain a noticeable hull vibration reduction of 65% at the exciting frequency of interest. Finally, this simple device is expected to be an inexpensive alternative for resolving vibration issues that arise from propeller cavitation.