An Exploratory Investigation of Mobile Breakwaters

Contract NBy-3143 was established to devise and investigate new schemes suitable for the development of mobile breakwaters. Mobile breakwaters are to be capable of attenuating various ocean waves sufficiently to provide a calm area for cargo-handling facilities. The devices investigated under this contract consisted of floatingplate absorbers, floating membranes, viscous blankets, and pneumatic wave mattresses. Results of tests on floating plate absorbers and membranes are not encouraging whereas the viscous blanket and pneumatic wave mattress seem promising. The viscous blanket gave satisfactory attenuation for wave lengths up to about twice the blanket length. The performance of the pneumatic wave mattress was slightly below that of the viscous blanket in this range, but exceeded the viscous blanket for wave lengths greater than twice the absorber length. Both units operated satisfactorily for a considerable range of wave lengths. it is felt that the preliminary results warrant further tests on both devices. A test program is recommended that would study effects of a variation of the various dimensional configurations of each of these two devices. Larger scale tests are also recommended, especially on the viscous blanket, in order to determine the significance of scale effects.