My boat is in a mud-berth. Will the Ultrasonic system be effective here?

The Ultrasonic antifouling system will keep clear only the part of the hull which is immersed in water. Therefore the part that sinks into the mud may attract growth in the usual way since the ultrasound will not penetrate the mud. However depending on the amount of time your boat dries out for or sits on the mud i.e. for only 2 hours will determine whether you consider is worth fitting the system or not.