Rim Driven Thruster -RDT

High Efficiency, Reduced Noise and Vibration

Sustainable Tunnel Thruster with motor and propeller in one compact unit

  • Efficient operation
  • High degree of manoeuvrability
  • Low noise and vibration
  • Compact design with savings in weight and space
  • No transmission losses
  • Reduced cost by system simplicity
A Green Solution - due to reduced emissions from great efficiency

RDT - Thruster design features

  • Compact electric RDT with thruster, propeller and Permanent Magnet motor in one unit
  • No need for external motor, shafts or couplings
  • Optimized propeller blade thickness and the radial load distribution is designed to enhance propeller efficiency
  • No oil pollution as the bearing design eliminates need for oil lubrication
  • Arrangement flexibility increased by the compact design
No central shaft and no shaft supporting struts improves propeller efficiency and reduces propeller induced noise and vibration.
Simple installation saves time and cost.

Starter characteristics

Direct On-Line starter

Starting current:

5-10x Nominal motor current (IN)

Pros:

Low price and high starting torque

Cons:

High in-rush current

Description:

The Direct On-Line (DOL) starter consists of a contactor and a protection device such as a circuit breaker. The contactor is energized when the start button is pressed, and the full line voltage is connected to the motor. Motor is started with propeller in zero pitch position (IZP).

Click the images to enlarge

Star-Delta starter

Starting current:

2-3x Nominal motor current (IN)

Pros:

In-rush current reduced with approx. 60% compared with DOL

Cons:

Reduced starting torque

Description:

The star-delta starter method applies reduced voltage to the motor, thus reducing current, during startup. This method requires that both ends of motor winding terminals are available. When connected in star each winding has less voltage (1 / √3 ~ 60%), and thus will have reduced starting current and torque. When full speed is reached the motor is connected in delta, having full torque available. Propeller pitch can be increased, and load applied when motor is connected in delta. Motor is started with propeller in zero pitch position (IZP).

Click the images to enlarge

Auto-Transformer

Starting current:

2-3x Nominal motor current (IN)

Pros:

In-rush current reduced with approx. 60% compared with DOL

Cons:

Reduced starting torque

Description:

Auto-Transformer also applies reduced voltage in steps to the motor during startup. The transformer voltage ratio can be designed to the application, typically having a 50-70% motor voltage during startup. The motor consumes less current at a lower starting voltage. For example, with a 50% tap on the Auto-Transformer, the motor draws half its rated current, or about 25% of what it would draw with a DOL starter. Motor is started with propeller in zero pitch position (IZP).

Click the images to enlarge

Electronic soft starter

Starting current:

2-2,5x Nominal motor current (IN)

Pros:

In-rush current reduced 

Cons:

Reduced starting torque.
Based on electronics

Description:

An electronic soft starter is a starting device that controls the way electricity is provided to the motor by using active switching devices such as thyristors. The device works in both in-line and in-delta configuration modes in three-phase motors. 

This starting method is ramping up the motor voltage in the starting sequence resulting in a reduced start-up current, allowing for a smooth and surge-free increase in motor torque. The voltage dips, stress, and wear and tear on the mechanical parts are all reduced as a result. Due to the thyristors there will be harmonic distortion of the current, and the influence on system voltage will depend on starting current and system impedance. Motor is started with propeller in zero pitch position (IZP).

Click the images to enlarge

Frequency converter starter

Starting current:

0,5x Nominal motor current (IN)

Pros:

In-rush current reduced.
Full speed and torque control

Cons:

THD generated, filters required.
Based on electronics

Description:

This is an electronic-controlled approach for starting asynchronous motors smoothly. It controls the frequency and current for the motor with electronics inverter circuits, avoiding large startup current. The thruster system's mechanical parts will be protected from high load because of the smooth start-up, and the this will also reduce the load on generators during startup compared to line-starter options. Depending on required performance torque and current may be below nominal values during startup. This is the high-end solution for the starting the thrusters, giving benefits such as smooth start, better energy economy, reduced wear and tear and process optimization.  Other benefits include motor speed stability during load changes and a longer motor life overall. Motor is started with propeller in zero pitch position (IZP).

Frequency converter starters may have different interface towards the main switchboard where 6-pulse rectifier is the most common, but both 12/24 pulse and Active Frontend (AFE) are used.6-pulse starters are the most common type, widely used due to the compact design and availability.The disadvantage with the 6-pulse starter is the increased THD during startup, particularly in smaller power system with large thrusters this might be an issue. 

To mitigate the THD a 12 or 24 pulse transformer and rectifier may be chosen, typically used for larger thrusters in larger ships. 
Frequency converter starters with active front end guarantees sinusoidal current and does not require a transformer. The AFE rectifier and LCL filter is more spacious than the 6-pulse rectifier and is suitable for high end solutions and ships with relatively small power system compared to thruster power.

Click the images to enlarge

Complete system deliveries

One source - one responsibility

For optimal performance Brunvoll takes responsibility for delivering complete systems and for providing support throughout the lifetime; from design, production, installation and commissioning, through daily operation.

Ask us for a complete thruster system including:

  • VFD for the motor
  • BruCon Control, Alarm and Monitoring system
  • BruCon Joystick and DP

Compile your vessel from Brunvoll's  product range

The wide product range of Brunvoll gives a unique configuration flexibility of integrated propulsion, manoeuvring and automation systems, see Propulsion Systems.

RIM DRIVEN THRUSTERS (RDT)

MODEL PROPELLER DIAMETER MM POWER RANGE KW
RDT 800 800 200
RDT 1000 1 000 300
RDT 1250 1 250 400
RDT 1500 1 500 600
RDT 1800 1 800 1 000
RDT 2100 2 100 1 400
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Technical Information

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Contact

Please contact us for any further information you may require about this solution

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Lars Myklebust

Lars Myklebust

Executive Sales Manager, Brunvoll AS

+47 905 19 704
lars.myklebust@brunvoll.no

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