Where does vibration come from?
Vibration can be caused by unbalanced or damaged air blades, loose mountings etc. However, the chief cause of mechanically transmitted noise lies in the design of the alternator itself. Light, high speed machines use alternators of a conventional radial configuration. They are built down to a price using a minimum of copper and magnetic material. The copper windings are placed on steel punchings which form the alternator’s magnetic circuit. When these punchings align with a magnet pole, a “hardspot” is felt. This phenomenon is called “cogging”. Cogging inhibits an early start-up in light winds and subsequently results in vibration down the mount tower and into the yacht’s accommodation. The D400 uses an axial field, ironless alternator. This rotates absolutely smoothly with no cogging, so there is no vibration to transmit. The D400 also uses very large, permanent magnets and heave copper windings. This enables the alternator to generate at low RPM, and the air blades to operate at a low TSR of 3.9, which keeps the airborne noise emission below 40 decibels.