There is several different, products that are used on ships to remove fouling with Ultra Sonic waves.

one is: Shipsonic Ultra Sonic Algae Remover for ships.

The Shipsonic is specially designed to prevent algae build-up under the ship’s waterline, there by preventing growth on the ship’s hull.
The Shipsonic produces an ultra-sonic wave pattern, which travels through polyester, metal and water and prevent the build-up of algae on the ship’s hull. The Shipsonic consists of an electrically powered 240 AC Volt electronic control box and a transducer, which is connected via a three-core 10-meter cable. The transducer is either installed inside the ship’s bilge in a holder, which is glued to the ship’s hull

http://www.shipsonic.com/shipsonic.english.info.html

Another use for Ultra Sonic Waves is cleaning of under water pipes.

Since fouling generated inside pipes of chemistry plant equipment, shortens “its life”, periodical maintenance such as cleaning or replacement is needed. Therefore, the development of a safe and sanitary method of preventing a corrosion and blockage inside pipes is desired. In this study, a vibration system, composed of a bolt-clamped Langevin transducer and a pipe, was employed to experimentally study the possibility of fouling removal. In the experiment, a flexural vibration was excited in a pipe containing fouling using ultrasonic waves. When the pipe was made to vibrate, with calcium carbonate or starch used as the fouling, it was shown that the fouling was diffused into the air, and except at the node of the flexural vibration, the fouling was removed completely. Also, the result showed that a higher input voltage to the transducer was more effective in removing the fouling.

http://www.jstage.jst.go.jp/article/jsmec/49/3/49_713/_article