24 August 2026
The 2 Main Shaft Generator Technologies Available Now
The growing adoption of Shaft Generators, and we are looking at the 2 main motor technologies, Electrical Excitation and Permanent Magnet.
Summary
BERG Propulsion’s M&G Shaft Generators: With the introduction of its M&G Shaft Generators, Berg Propulsion brought into the market a technology that supports continuous operation of ships at any propeller speed, from zero speed to maximum rpm, including in heavy seas.
WE Tech Solutions’ Permanent Magnet Shaft Generators: Using variable frequency drive technology (WE Drive™), DC-link power distribution, permanent magnet generator, and Energy Management System(EMS).
RENK’s Shaft Generators: The traditional method is to mount shaft generators in the vessel’s stern at the propeller shaft. But this approach limits the widespread use of the shaft generator system, since this is not feasible for all ships. Therefore, their technology allows shipowners to easily connect shaft generators to the crankshafts of their ships’ main engines.
SMDERI Shaft Generators: The Shanghai Marine Diesel Engine Research Institute (SMDERI) Shaft Generator can be mounted directly on the intermediate shaft, and it is not required to replace the ship’s shaft system. Hence, minimizing the retrofit time without the need for Dry Docking. It has been a trusted and emission-free energy solution since 2007, with more than 200 applications worldwide.
The Differences between EESG and PMSG: Both the Externally Excitation Synchronous Generator (EESG) and the Permanent Magnet Synchronous Generator (PMSG) are useful synchronous generators for producing power in the marine industry. However, there are some striking differences between EESG and PMSG.
Table of Contents
BERG Propulsion’s M&G Shaft Generators
The Sweden-based Berg Propulsion AB is one of the companies currently providing alternative sources of power to drive shipping operations through its marine propulsion systems. With the introduction of its M&G Shaft Generators, Berg Propulsion brought to the market a technology that supports the continuous operation of ships at any propeller speed, from zero speed to maximum rpm, including heavy seas sailing. [1]
Characteristics of BERG Propulsion’s M&G Shaft Generators
- Flexibility, reliability, and achieving high performance
- Reduce operational costs and minimize fuel consumption
- Greater efficiency and compliance with environmental legislation
- Function well with limited maintenance
- Reduce the extent of vibration and noise during use
Shaft Generators: The Next Step in Ship Efficiency Improvement
Shaft generators offer shipowners the unique opportunity to save on energy or fuel expenses while prolonging the longevity of their vessels’ engines
Ship Nerd
WE Tech Permanent Magnet Shaft Generators
In a genuine effort to encourage zero-emission maritime operations, WE Tech Solutions uses variable frequency drive technology, DC-link power distribution, permanent magnet generator, and Energy Management System (EMS). [2]
Characteristics of WE Tech Solutions’ Permanent Magnet Shaft Generators
- Lead to significant fuel savings and sharp lowering of operational costs
- Not completely depending on Auxiliary Generator operation
- Specifically available for upgrade projects (retrofits)
Types of Permanent Magnet Shaft Generators
There are two kinds of WE Tech Solutions’ Permanent Magnet Shaft Generators:
- Direct drive permanent magnet shaft generator for 2-stroke (slow speed) applications
- Permanent magnet rotor mounted on the intermediate shaft of the propulsion system.
- Low mass and inertia, with minimal impact on propulsion system torsional vibration calculations (TVC)
- Not requiring additional bearings, and the propeller shaft system design is left uncompromised.
- The compact generator housing has feet feet-mounted stator package, with the rotor and intermediate shaft positioned on the generator bed in the propeller shaft line and connected via flanges.
- For 4-stroke (Medium Speed) Applications
- Solution One concentrates on the energy-saving operation of any vessel equipped with direct-driven propulsion machinery, combined with a Power Take Out (PTO) system.
- Enable the operation of propulsion machinery in combinator mode – variable speed and pitch of the propeller
- The Shaft Generator is online, generating power for the ship’s electrical network
- Propulsion machinery can be operated at optimal duty points at all vessel speeds
- Enhance energy efficiency by reducing fuel consumption and cutting down environmentally harmful emissions
RENK’s Shaft Generators
RENK’s shaft generators are built to liberalize the utilization of shaft generating systems in the shipping industry. The traditional method is to mount shaft generators in the vessel’s stern at the propeller shaft. But this installation approach limits the widespread use of the shaft generating system, since it is not feasible for all ships. Therefore, RENK’s technology allows shipowners to easily connect shaft generators to the crankshafts of their ships’ main engines. [3]
RENK’s Shaft Generator Technologies
RENK offers two types of shaft generating systems to help shippers generate emission-free and economical energy/power efficiently. They include:
- The IFPS—which is a compact and powerful solution that can easily be connected to the crank shaft of the main engine, providing several benefits. IFPS is designed in a way that the tunnel gear uses the propeller shaft and provides a PTO/PTI solution through gear stages. The compact, flexible design facilitates an upgrade of the solution to a PTI system.
- MARHY— with PTI functionality, MARHY is a complete solution for shipowners to add a hybrid propulsion system and generate enough energy to power their marine operations. In addition to having a shaft generator, MARHY also comes with a complete PTO/PTI solution. This solution enhances fuel efficiency as well as providing a second drive system.
SMDERI Shaft Generators
The Shanghai Marine Diesel Engine Research Institute (SMDERI) Shaft Generator has been a trusted and emission-free energy solution since 2007, with more than 200 applications worldwide.
Some of the qualities of the SMDERI Shaft Generators that shipowners appreciate include achieving:
- Engine Power Limitation (EPL) of up to 10%.
- Energy Efficiency Existing Ship Index (EEXI) of up to 12%.
- Energy Efficiency Design Index (EEDI) of up to 5%; and
- Carbon Intensity Indicator (CII) of up to 5%.
As a result of its non-bearing design and a special split-half structure, a SMDERI shaft generator can be mounted directly on the intermediate shaft, and it is not required to replace the ship’s shaft system. The split setups make it possible for SMDERI shaft generators to prevent a ship’s Dry Docking, subsequently reducing the installation period to just 9 days while floating at any berth.
Electrical Excitation vs Permanent Magnet
Both the Externally Excited Synchronous Generator (EESG) and the Permanent Magnet Synchronous Generator (PMSG) are useful synchronous generators for producing power in the marine industry. However, there are some striking differences between EESG and PMSG, which are highlighted in the table below:
| The motor can generate electricity when it is running, and it can generate electricity when the output voltage reaches the input requirement of the inverter module, but it can not generate electricity when it exceeds the over-speed range. | EESG | PMSG | ||
| Shaft Generator | Form of excitation | Electrical Excitation | Permanent Magnet | |
| Machine efficiency | Machine efficiency ≥ 94% | Machine efficiency ≥ 96% | ||
| Output voltage | Output constant voltage | Voltage fluctuation with speed | ||
| Output power | Constant power output on request, power reduction range is generally 20% of the rated speed, beyond the required speed range can still be extended to generate electricity | The stator and rotor need to be cooled, which can be divided into two types: water jacket cooling and air-water cooling. | ||
| Cooling form | Only the stator can be cooled, which can be divided into two kinds of water jacket cooling and air water cooling, air water cooling can be in the cooling system after the failure of continuous operation | Only the stator can be cooled, which can be divided into two kinds of water jacket cooling and air-water cooling. Air water cooling can be used in the cooling system after the failure of continuous operation. | ||
| Neutral point circuit breaker | Permanent magnet motors generally weigh 10-15% less than excitation motors, the main weight reduction is in rotors. | |||
| Rotor mounting form | For newbuilding, motor is generally mounted on the intermediate shaft bosses. For retrofit, motor is mounted on the yokes. | Bilateral AFE dynamic response and compensation are better than AFE+DFE | ||
| Means of demagnetization after failure | Cutting off power to the excitation circuit | Mounted on the yoke, the yoke is connected to the intermediate shaft by a flange in newbuilding projects, and the yoke is connected to the intermediate shaft by a tensioning sleeve on retrofit projects (SMDERI design). | ||
| Converter | Inverter Module Type | For newbuilding projects, motors are generally mounted on the intermediate shaft boss. For retrofit projects, motors are mounted on the yokes. | Bilateral AFE | |
| minimum Input Frequency | 2.6Hz/5Hz | 5Hz | ||
| Input Voltage Range | Bilateral AFE dynamic response and compensation are better than AFE+DFE | Net-side output voltage ±20% | ||
| Output Dynamic Response | Bilateral AFE dynamic response and compensation better than AFE+DFE | |||
| Excitation control | External control systems (can be classified as thyristors, DC-DC, transformers, etc.) | No need | ||
| Transformers | Standard or not | Depending on the voltage class, generally standard on container ships and medium voltage systems | Standard Equipment | |
| System Performance | System efficiency | ~90% | Troubleshooting is generally carried out by disconnecting the power supply from the excitation circuit, and in the case of serious motor failure, carrying out the necessary dismantling of the motor for maintenance of the fault. | |
| Service ability | Troubleshooting is generally carried out by disconnecting the power supply from the excitation circuit, and in the case of serious motor failure, carry out the necessary dismantling of the motor for maintenance of the fault. | Troubleshooting requires disconnecting the neutral switch, disengaging the rotor from the intermediate shaft if necessary, and going into the dock for maintenance on important faults. | ||
| Load Losses | No | Yes | ||
| Maintenance cost | Relatively low | Relatively low | ||
| System cost | Permanent magnet shaft generator systems cost 10-15% more than excitation shaft generator systems | |||
Key Takeaways
There is no doubt that the five existing shaft generating technologies offer significant hope for shipowners to operate their vessels continuously and cost-effectively, while complying with important environmental regulations. The five shaft generating systems, analyzed in this article, utilize either EESG or PMSG technology, and the differences in the two technical approaches, in terms of their performance, transformers, converters, and shaft generating sets, are highlighted in Table 1 above.
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