2-speed Gearboxes

Great advantages and flexibility with 2-speed gearbox systems

Great advantages with a 2-speed CP-propulsion system giving optimised running conditions and considerable energy savings

An energy efficient solution

The 2-speed reduction gearbox is a fully integrated solution to provide the option for two steps of different propeller speed in a hybrid or diesel mechanical configuration. The system is ideal for vessels with variations in power requirements, such as Purse Seiners, Trawlers, AHTS, Seismic vessels, Mega Yachts and Rescue vessels.
  • Designed for reduced fuel consumption in low rpm conditions
  • Ideal for configurations requiring power generation from the main engine to the main swithchboard during operation
  • Ideal for hybrid configurations requiring boost, Power Take Home (PTH) and/or diesel electric running mode

Reduced propeller rpm - reduced energy consumption

The graphs of Step1 and Step2 in the diagram show the direct effect of reducing the rpm using the 2-speed reduction gearbox.
  • The configuration consists of a Main Engine (ME) and a generator in PTO-condition. By designing optimum power distribution to the propeller and utilising the remaining power to the PTO, there will be full utilisation of the available power from the Main Engine. 
  • In Step1 the Main Engine run the propeller via the main gear ratio. Simultaneously the Shaft Generator is driven via the PTO gear set. This mode is useful when the power demand for propeller is high and the electric prower production demand is low. In this condition the propeller is highly efficient provided it is optimised for this condition.
  • In Step2 the Main Engine run the propeller via the PTO gear that further transmit the mechanical power over the PTI gear set -via the main gear ratio to the propeller. Hence, because of the choosen PTO- and PTI- gear ratios, the propeller run at lower rpm, compared with Step1. The condition is typical when propeller power demand is in lower range, and because of the reduced propeller speed the propulsion efficiency is maintained relatively high. The Main Engine run at its nominal speed that make possible a high electric power production by the Shaft Generator.

Odd Lundberg reports about great savings with 2-speed CP-Propulsion System

The pelagic vessel Odd Lundberg, owned by the Norwegian fishing company Odd Lundberg, is designed with a strong focus on optimal working conditions, safety and comfort for the crew. “We are generally very proud of our vessel,” said Mats Lundberg, Odd Lundberg’s skipper. “The performance and the new technology means that we can save time and fuel when we are at sea, and this means more time at home with our families and friends."

The collaboration between the owner, the Karstensens shipyard and Brunvoll resulted in an effective and sustainable solution for propulsion and manoeuvring, based on the vessel's operating profile. The 2-speed propulsion system allows for operation in two speed modes, ensuring optimisation of propeller speed and energy consumption in different operating conditions, a system that has proven to provide significant savings.

"We have used step two of the system to a much greater extent than first expected. We experimented with the plant during trawling, and to our surprise we experienced that trawling by using step two and the 50-60 Hz floating frequency resulted in a fuel consumption decrease by 100-130 litres per hour. With 12-20 hours spent in that condition per day for much of the year, such savings are very positive," Mats Lundberg said.

Design principles of a 2-speed gearbox

The 2-speed gearbox design and construction is based on the same principles as for all Brunvoll gearboxes, and benefit from a reliable high quality philosophy.

The gear housing is as standard made from high quality grey cast iron, designed with high stiffness and good vibration damping property. However, nodular cast iron is available as option (typical in high Ice class applications).

Gears are designed and manufactured with high precision and optimised for high load, low vibratory excitation and long lasting. Extensive use of sliding bearing (long lasting) for both journal bearings and thrust bearings. Clutches are of high capacity, hydraulically operated, multiple disc, oil lubricated type.

Gearbox fulfil all Class Society requirements.

The gearboxes are designed in 3D and analysed for full load to ensure excellent performance.

The Brunvoll 2-speed gearbox program

Size Vertical Offset Power Range kW*
ACG 680 2SP x 2200 - 4400
ACG 750 2SP x 2500 - 5200
ACG 850 2SP x 3000 - 6000
ACG 980 2SP x 3700 - 10500
ACG 1080 2SP x 4500 - 12000
Standard range of Brunvoll 2-speed gearboxes.
* The power range for each gearbox depends on selected rpm and eventual ice notation.

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
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Technical Information

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Download the product sheet available to see more

References

Selected Brunvoll references

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Contact

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Arnfinn Brautaset

Arnfinn Brautaset

Sales Manager, Brunvoll Volda AS

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

Vidar Liaskar

VP Sales, Brunvoll Volda AS

+47 952 57 129
vidar.liaskar@brunvoll.no

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