An electric ring thruster as auxiliary manoeuvring propulsion system for watercraft – construction analysis

Abstract

The reported project aimed at examining properties and purposefulness of use of modern electromagnetic bearings for a screw propeller in a prototype version of a synchronous ring motor with rare earths magnets. Bearings of this type generate electromagnetic forces which keep the rotor in a state of levitation. The rotating machine with magnetic bearings can work in any environment which reveals diamagnetic properties (air, vacuum, water, liquid gases, etc.). However, a basic quality of the magnetic bearings is elimination of cooling installation and lubrication, which is necessary for proper operation of rotating machines with rolling and slide bearings, undergoing wear with time. Therefore the lifetime of the machine supported on magnetic bearings is incomparable with others. Also torque losses on this bearing are the smallest, compared to all known types of bearings. Ring thrusters can be used as the main drive for relatively small sea-going and inland vessels, and as manoeuvring drive for ships of arbitrary size, especially for AES (All Electric Ship) type vessels. This type of propeller is extremely useful for any types of abyssal vessels, autonomous and remotely controlled, and on submarines. It can also be used as effective generator of electric current for charging batteries in towing trains, barges for instance. The project consisted of three research tasks: 1. Designing, manufacturing and examination of a magnetic bearing on-line controlled by a digital controller, 2. Manufacturing a model of a ring thruster and examination of characteristics of a propeller mounted in the ring, 3. Examining the ferrofluid seal. A concept of the new thruster is a consequence of investigations carried out in Poland upon propellers and magnetic bearings in years 2001-2005.