The rim-driven thruster, also known as rim-driven propulsor/propeller (or RDP) is a novel type of electric propulsion unit for ships. The concept was proposed by Kort around 1940, but only became commercially practical in the early 21st century due to advances in DC motor controller technology. [1] As of 2017, commercial models of between 500 kW and 3 MW are available from manufacturers such as Rolls-Royce, Schottel, Brunvoll, Voith, Van der Velden, etc.
The rim-driven thruster is a marine propeller that does not use a central hub for transmission of the driving torque. Conventional hubcentric propellers typically use a shaft driven by a turbine, a diesel engine or an electric motor. The more recent podded drives consist of a propeller driven by a conventional electric motor into an azimuthable gondola under water, but they still incorporate a traditional hubcentric propeller.
The blades of the rim-driven thruster, by contrast, are mounted on an outer ring rather than a central hub. The ring constitutes the rotor of an electric motor and sits within a surrounding stator, which is also ring-shaped and creates the necessary torque. Rotor and stator are water tight and the whole unit operates submerged. Similar to an azipod, a rim-driven thruster can be designed to be fixed, retractable and/or azimuthing.
The largest advantages of the rim-driven thruster are lower noise emissions, potentially increased efficiency, and a compact design that enables relatively simple integration in many applications. Since the propeller blade/rotor assembly is driven directly by electro-magnetic forces, no shaft and no gearbox is needed. The blades can be made of metal or composite material, and the rotor and stator can be hermetically sealed. Since the blades are mounted to the rotor ring, there is no tip gap (which can be a noise source in ducted propellers) and the elimination of a mechanical gearbox also removes a prominent sources of noise.
The primary disadvantage is the complexity of manufacturing high-output submerged motors with water-lubricated bearings. The potential efficiency improvements might also be tricky to achieve due to friction losses in the gap between the rotor and its surrounding stator. And as with all high-output electric motors, sufficient cooling can present problems even for units submerged in water.
A propeller is a device with a rotating hub and radiating blades that are set at a pitch to form a helical spiral which, when rotated, exerts linear thrust upon a working fluid such as water or air. Propellers are used to pump fluid through a pipe or duct, or to create thrust to propel a boat through water or an aircraft through air. The blades are shaped so that their rotational motion through the fluid causes a pressure difference between the two surfaces of the blade by Bernoulli's principle which exerts force on the fluid. Most marine propellers are screw propellers with helical blades rotating on a propeller shaft with an approximately horizontal axis.
An electric motor is an electrical machine that converts electrical energy into mechanical energy. Most electric motors operate through the interaction between the motor's magnetic field and electric current in a wire winding to generate force in the form of torque applied on the motor's shaft. An electric generator is mechanically identical to an electric motor, but operates with a reversed flow of power, converting mechanical energy into electrical energy.
In aeronautics, a ducted fan is a thrust-generating mechanical fan or propeller mounted within a cylindrical duct or shroud. Other terms include ducted propeller or shrouded propeller. When used in vertical takeoff and landing (VTOL) applications it is also known as a shrouded rotor.
An azimuth thruster is a configuration of marine propellers placed in pods that can be rotated to any horizontal angle (azimuth), making a rudder redundant. These give ships better maneuverability than a fixed propeller and rudder system.
A propulsor is a mechanical device that gives propulsion. The word is commonly used in the marine vernacular, and implies a mechanical assembly that is more complicated than a propeller. The Kort nozzle, pump-jet and rim-driven thruster are examples.
Contra-rotating, also referred to as coaxial contra-rotating, is a technique whereby parts of a mechanism rotate in opposite directions about a common axis, usually to minimise the effect of torque. Examples include some aircraft propellers, resulting in the maximum power of a single piston or turboprop engine to drive two propellers in opposite rotation. Contra-rotating propellers are also common in some marine transmission systems, in particular for large speed boats with planing hulls. Two propellers are arranged one behind the other, and power is transferred from the engine via planetary gear transmission. The configuration can also be used in helicopter designs termed coaxial rotors, where similar issues and principles of torque apply.
Aircraft equipped with contra-rotating propellers, also referred to as CRP, coaxial contra-rotating propellers, or high-speed propellers, apply the maximum power of usually a single piston or turboprop engine to drive a pair of coaxial propellers in contra-rotation. Two propellers are arranged one behind the other, and power is transferred from the engine via a planetary gear or spur gear transmission. Contra-rotating propellers are also known as counter-rotating propellers, although the term counter-rotating propellers is much more widely used when referring to airscrews on separate non-coaxial shafts turning in opposite directions.
The Voith Schneider Propeller (VSP) is a specialized marine propulsion system (MPS) manufactured by the Voith Group based on a cyclorotor design. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.
A Z-drive is a type of marine propulsion unit. Specifically, it is an azimuth thruster. The pod can rotate 360 degrees allowing for rapid changes in thrust direction and thus vessel direction. This eliminates the need for a conventional rudder.
An impeller or impellor is a driven rotor used to increase the pressure and flow of a fluid. It is the opposite of a turbine, which extracts energy from, and reduces the pressure of, a flowing fluid.
Azipod is a trademark azimuth thruster pod design, a marine propulsion unit consisting of a fixed pitch propeller mounted on a steerable gondola ("pod") containing the electric motor driving the propeller, allowing ships to be more maneuverable. They were developed in Finland in the late 1980s jointly by Wärtsilä Marine, Strömberg and the Finnish National Board of Navigation.
The tail rotor is a smaller rotor mounted vertically or near-vertically at the tail of a traditional single-rotor helicopter, where it rotates to generate a propeller-like horizontal thrust in the same direction as the main rotor's rotation. The tail rotor's position and distance from the helicopter's center of mass allow it to develop enough thrust leverage to counter the reactional torque exerted on the fuselage by the spinning of the main rotor. Without the tail rotor or other anti-torque mechanisms, the helicopter would be constantly spinning in the opposite direction of the main rotor when flying.
MS Arcadia is a cruise ship in the P&O Cruises fleet. The ship was built by Fincantieri at their shipyard in Marghera, Italy. At over 84,000 gross tonnage (GT), Arcadia is the second smallest of seven ships currently in service with P&O Cruises. The ship officially entered service with the company in April 2005 and was named by Dame Kelly Holmes.
Manoeuvering thrusters are transversal propulsion devices built into, or mounted to, either the bow or stern, of a ship or boat to make it more manoeuvrable. Bow thrusters make docking easier, since they allow the captain to turn the vessel to port or starboard side, without using the main propulsion mechanism which requires some forward motion for turning; The effectiveness of a thruster is curtailed by any forward motion due to the Coandă effect. A stern thruster is of the same principle, fitted at the stern. Sufficiently large vessels often have multiple bow thrusters and stern thrusters.
A hydraulic motor is a mechanical actuator that converts hydraulic pressure and flow into torque and angular displacement (rotation). The hydraulic motor is the rotary counterpart of the hydraulic cylinder as a linear actuator. Most broadly, the category of devices called hydraulic motors has sometimes included those that run on hydropower but in today's terminology the name usually refers more specifically to motors that use hydraulic fluid as part of closed hydraulic circuits in modern hydraulic machinery.
An L-drive is a type of azimuth thruster where the electric motor is mounted vertically, removing the second bevel gear from the drivetrain. Azimuth thruster pods can be rotated through a full 360 degrees, allowing for rapid changes in thrust direction and eliminating the need for a conventional rudder. This form of power transmission is called a L-drive because the rotary motion has to make one right angle turn, thus looking a bit like the letter "L". This name is used to make clear the arrangement of drive is different from Z-drive.
A drum motor is a geared motor drive enclosed within a steel shell providing a single component driving pulley for conveyor belts.
Schottel is a manufacturer of propulsion and steering systems for ships and offshore applications. The company founder Josef Becker invented the rudderpropeller, a z-drive, in 1950. Today the company develops and manufactures azimuth propulsion, maneuvering and steering systems. In 2014 the subsidiary Schottel Hydro was founded to bundle up the company activities in the hydrokinetic energy segment.
An underwater thruster is a configuration of marine propellers and hydraulic or electric motor built into or mounted to an underwater robot as a propulsion device. These give the robot movement and maneuverability against sea water resistance. The main difference between underwater thrusters and marine thrusters is the ability to work under heavy water pressure, sometime up to full ocean depth.
A marine thruster is a device for producing directed hydrodynamic thrust mounted on a marine vehicle, primarily for maneuvering or propulsion. There are a variety of different types of marine thrusters and each of them plays a role in the maritime industry. Marine thrusters come in many different shapes and sizes, for example screw propellers, Voith-Schneider propellers, waterjets, ducted propellers, tunnel bow thrusters, and stern thrusters, azimuth thrusters, rim-driven thrusters, ROV and submersible drive units. A marine thruster consists of a propeller or impeller which may be encased in some kind of tunnel or ducting that directs the flow of water to produce a resultant force intended to obtain movement in the desired direction or resist forces which would cause unwanted movement. The two subcategories of marine thrusters are for propulsion and maneuvering, the maneuvering thruster typically in the form of bow or stern thrusters and propulsion thrusters ranging from Azimuth thrusters to Rim Drive thrusters.