The document discusses ultrasonic anti-fouling as an alternative to present ship hull cleaning methods. Current methods use biocide paints or cleaning the hull in dry dock, which are expensive and harm the environment. Ultrasonic anti-fouling works by attaching actuators to the hull to vibrate it at ultrasonic frequencies of around 40 kHz, preventing biofouling from adhering while having minimal effect on biocide coatings. It can clean ship hulls while in motion and has no restrictions, making it more cost effective than existing cleaning methods.