CRP Contra Rotating Propellers

The optimum electric propulsion system for single screw vessels

"Potential savings of CRP are assessed to be in the order of 6-20% of the power consumption with an average of 13%, although higher figures may be presented by industry for specific case"

Contra Rotating Propellers (CRP)

  • A complete propulsion system with Contra Rotating Propellers in a redundant single screw configuration, class approved for two electric motors.
  • A configuration of fixed pitch propellers individually driven through a unique shaft-in-shaft system.
  • This propulsion system recovers part of the slipstream rotational energy, which is lost with single propeller configurations, and thereby enhances the hydrodynamical efficiency.
  • The blade numbers of the two propellers are usually different to avoid vibrational problems.
  • The aft propeller diameter is smaller in order to stay within the slipstream contraction from the forward propeller.
  • The system can be driven by any type of electric motors.
Juanita Platform Supply Vessel, with Brunvoll CRP Contra Rotating Propulsion System
Juanita, PSV equipped with Brunvoll CRP system. (Photo: Helge Brandal)

System benefits

  • Efficient
  • Robust
  • Redundant
  • Protected Propellers

Explore our new series of Contra Rotating Propulsion Systems

Brunvolls core competence in propulsion and gearbox design has been utilised in this new series of the Contra Rotating Propulsion System -a combination of known technologies.

There is an "off the shelf" series of standard configurations consisting of 2 asynchronous electric motors and variable frequency drives, standardised gearboxes and propellers with predefined diameter and rpm, with BruCon Remote Control and Monitoring System.

Blade designs will be customised to the ship for optimum performance.

Brunvoll CRP may also be optionally configured for other extensive prime mover solutions, such as a combination of electric motors and any kind of combustion engines with or without shaft generators.

Brunvoll Contra Rotating Propulsion System with gearbox and two electric motors
Brunvoll Contra Rotating Propulsion System Arrangement with gearbox and two electric motors.
Brunvoll CRP Contra Rotating Propeller in hull design
Brunvoll CRP Contra Rotating Propeller Shaft in Shaft arrangement
Brunvoll CRP Contra Rotating Propeller Shaft seal arrangement DnV Clean Design

Shaft and Gearbox Arrangement

  • Outboard shaft seals complies with DNV Clean Design notation as standard
  • Propeller thrust bearings are of robust Mitchell tilting pad type, integrated in the gearbox for easy inspection and maintenance
  • Stern tube with oil lubricated white metal bearings
  • Monitoring system for Contra Rotating Bearings
  • Low noise lubrication oil pumps driven by electrical motors
  • Oil purifiner in addition to oil filter system for gearbox as standard.

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
No items found.

Technical Information

Interested in further information about this product?
Download the product sheet available to see more

References

Selected Brunvoll references

See all references
Related content

Read more

Related Products

See all products

Contact

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

See all contacts
Per Endre Woldsund

Per Endre Woldsund

Sales Manager, Brunvoll Volda AS

+47 905 72 814
per.woldsund@brunvoll.no
Arnfinn Brautaset

Arnfinn Brautaset

Sales Manager, Brunvoll Volda AS

+47 915 77 678
arnfinn.brautaset@brunvoll.no

Curious about this product?

Request for information about our solutions, products and services

Send request