Rolls-Royce 1,600 kW permanent magnet tunnel thruster. Click to enlarge.

The permanent magnet tunnel thruster design concept comprises a permanent magnet motor in a rim, which drives the propeller in the center. The permanent magnet motor consists of two main parts:a stator that carries a number of electrical coil windings, and a rotor fitted with a number of very strong permanent magnets. A rotating magnetic field is created by the stator which interacts with the fields of the permanent magnets on the rotor, which generates force to drag the rotor around, providing the mechanical power.

PM thrusters are currently available in two sizes with powers of 1,000 and 1,600 kW, with maximum output thrust of 143 and 216 kN, respectively.

Other benefits of permanent magnet technology include the freeing up of space directly above the thruster where traditional tunnel thruster motors are located, and a symmetrical design that gives equal thrust to port or starboard. It is available in 1600mm and 2000mm diameter.

We are delighted that Norwegian Cruise Line is the first cruise customer to select our new permanent magnet tunnel thruster as an upgrade to an existing propulsion package. Passenger comfort is a top priority for cruise lines, and the reduction of both noise and vibration, which our permanent magnet technology provides, is of paramount importance to successful cruise operators like NCL.

This highly innovative and cutting edge permanent magnet technology is suitable for a range of applications in both merchant and offshore vessels, where exceptionally low noise levels, high power output, and rapid response to power demand will benefit operators, crew and, very importantly, passengers alike.

What we have seen so far through the experience of our first permanent magnet tunnel thruster in operation on the Rolls-Royce designed Olympic Octopus, a highly advanced offshore anchor handling vessel, is that a permanent magnet motor thruster is quiet, efficient and durable. It is capable of running for thousands of hours in intensive dynamic positioning (DP) mode, where rapidly varying loads and alternating thrust directions are the norm.

—Jay McFadyen, Senior Vice President - Marine Services, Americas, Rolls-Royce