YANMAR Technical Review

Abstract

In recent years, the marine industry has seen growing demand for electrification to reduce environmental impacts and enhance comfort. Yanmar has developed a hybrid system for pleasure boats called YF12e that incorporates electric motor drive and power generation using the engine and electric motor in tandem. Building on this product, Yanmar intends to promote the commercialization of electrified products designed to reduce environmental impact and improve comfort.

1. Introduction

The marine industry over recent years has seen rising expectations for the electrification of boats to reduce environmental impact and enhance comfort. Yanmar meanwhile has been developing a variety of electrified products to make them available for use in a wide range of boats, including both pure electric propulsion systems suitable for low-power and short-duration use and hybrid systems for high-power and long-duration use.
Yanmar has now launched its first hybrid system. In addition to electric motor propulsion that ensures comfort by combining zero exhaust gas emissions with minimal vibration and noise, the system also incorporates a generation function that can charge the batteries when external charging infrastructure is not available.
This article describes the product concept behind Yanmar’s YF12e marine hybrid system and the market reaction.

2. YF12e Product Concept

The newly developed YF12e is targeted at pleasure boats in which people spend long periods of time without running at high speeds, such as canal boats used on inland waterways or yachts that primarily run under sail. Fig. 1 shows an example of a canal boat. As boats are propelled by the rotation of an underwater propellor, they differ from wheeled vehicles found on land in that they often run continuously at maximum shaft speed and do not provide any opportunity for regeneration when slowing down. Moreover, as shown in Fig. 2, the sort of boats targeted for the YF12e have onboard appliances such as refrigerators or air conditioners, the use of which necessitates a dedicated generator engine.
All of this makes it important that marine hybrid systems can propel craft comfortably at low speed, allow for the use of the onboard appliances that make spending extended periods of time onboard more pleasant, and produce minimal engine or other noise. Table 1 lists the design concept for the YF12e that is intended to satisfy these requirements.

Table 1 Boat User Requirements and YF12e Concept

3. Technologies Used in Hybrid System

Fig. 3 shows a system diagram and Table 2 lists the specifications for the YF12e system developed to achieve the product concept described above. The system was built by transforming an existing Yanmar-developed propulsion engine into a hybrid system through the addition of lithium-ion batteries, an electric motor, and an inverter. As the electric motor is used for both propulsion and generation, the generator engine installed on boats in the past is no longer required.
The following sections provide details of the technologies used to implement the hybrid system.

Table 2 YF12e Specifications

3.1. Low-Speed Running with Electric Motor Drive

To satisfy the above requirements, the hybrid system includes the ability to run on electric motor propulsion, which does not produce any exhaust emissions. The electric motor output was selected to satisfy requirements for both boat speed and electricity generation. Moreover, the gear ratio used by the power train with electric motor was chosen to be optimal for its torque characteristics, thereby enabling the boat to move at speeds that would be too low to achieve under engine power. The throttle is also more responsive when running with electric motor drive, providing finer control over speed than engine drive.
On the other hand, adoption of the hybrid system created a need to minimize the noise from the marine gear and other peripheral equipment. While this is not especially noticeable when running on engine drive, the concern was that it would become much more obvious when running at low speed using the electric motor. Accordingly, the design sought to minimize gear noise, even when running the electric motor at high speed, by optimizing the gear meshing conditions for all gears in the power train. Similarly, the system controls the pumps used to supply lubricating oil and cooling fluid in a way that reduces pump pulsation noise and vibration, turning pumps on or off and adjusting their speed based on equipment temperature and other operating conditions.

3.2. Combined Propulsion and Generation Capabilities and Provision of Long-Duration Power Supply

As the hybrid system uses the propulsion engine to generate electric power, with the engine speed changing depending on whether the boat is speeding up or slowing down, the situation is different to when there is a dedicated generator engine. Moreover, the upper limit on engine speed would need to be reduced were electricity generation to use the gear ratio for electric motor drive, resulting in a lack of propulsion power.
To resolve this problem, the hybrid system is equipped with separate power train configurations with different gear ratios for electric motor drive and generation respectively, and a clutch for switching between them. The layout is shown in Fig. 4. By using the clutch to switch between the power train configurations for these respective operating modes, the hybrid system can maintain propulsion power when underway while still being able to make use of the full engine speed range when generating power, as shown in Fig. 5. Moreover, the addition of control mechanisms for synchronizing gear speeds in the transmission and for switching between power train configurations means that generation can be started or stopped at any time, regardless of boat or engine speed.
The system can use the generated electric power for more than just electric motor drive and charging the lithium-ion batteries, also being configured to supply electric power to onboard appliances such as a refrigerator or air conditioner. This means that these onboard appliances can be left turned on for a long time without having to start up the engine, such as when staying on the boat overnight or when moored at a location where no external power connection is available.

3.3. Control Interface Designed for Ease of Use

Another requirement for the hybrid system was to allow the operator to use the display to change operating modes whenever they want. In addition to the start-up and shutdown operations used in a conventional engine-only configuration, this also includes actions such as selecting electric motor drive or starting or stopping generation. The concern with this, however, was that the growing number of functions would make it harder for the operator to keep track of all the different modes and detract from their ability to switch between them intuitively. It was also anticipated that the various ways in which the hybrid system’s operating modes change the energy pathways would likewise make it harder for the operator to understand the different modes. For these reasons, the ease-of-use and presentation of the control interface was recognized as an issue that needed to be addressed.
For ease-of-use, icons are used to represent the different operating modes in the mode switching screen, as shown in Fig. 6, and a touch panel display is used for direct fingertip operation just like a smartphone or tablet computer. These features make it obvious to anyone how to switch between modes.
To address the issue of screen presentation, the design shown in Fig. 7 was adopted. Here, the different drive train configurations are presented intuitively to make the operating modes easier to understand. Engine, electric motor, battery, and propellor icons are used in addition to the operating mode names, and the energy flows between icons are represented graphically.

4. Market Reaction

The following sections describe the customer feedback received when the system was installed in a canal boat used to run the inland waterways of France.

4.1. Market Reaction to Electric Motor Drive

Optimizing the power train gear ratio used with electric motor drive to suit the motor characteristics made it possible for the boat to run more slowly than would be possible under engine power, as shown in Fig. 8. This feature received positive feedback, with a user commenting that it allowed the boat to be maneuvered slowly and with care for nearby boats and obstacles in the marina and other speed-restricted areas. The responsiveness of the electric motor was also acknowledged, with the comment being made that speed control was easier than for conventional engine drive and that this made the boat easy to handle in canals or other narrow waterways.
Users also appreciated how a hybrid configuration allows them to choose the power source to suit the conditions, with the option of engine drive being available for use on fast flowing rivers or in strong winds or other heavy weather conditions.
Another benefit is that electric motor drive is 13dB(A) quieter than when using the engine, as shown in Fig. 9. Users appreciated this reduction in vibration and noise compared to engine drive, commenting that the quietness with electric motor drive made the boat a more pleasant place to be.

4.2. Market Reaction to Electricity Generation and Supply

While the canals where the trial boat operated offered little in the way of external charging infrastructure, the generation function meant that the lithium-ion batteries could still be charged even when the boat was under power, with the generation output being dependent on the boat speed. When moored, as the generator output varies with engine speed as shown in Fig. 10, the operator can adjust the rate of charge by changing the engine speed. This means that the batteries can be charged whenever needed and avoids having to go searching for somewhere to recharge out of concern for the remaining battery charge.
Prior to installing the hybrid system, the canal boat used a dedicated generator engine to supply the power to the onboard appliances, which included a refrigerator and air conditioner. This required the engine to run continuously when someone was staying onboard. The new system, in contrast, can supply power to the onboard appliances from the lithium-ion batteries for extended time periods without running the engine.
The comfort and convenience provided by these features were highly regarded. Even when no external charging is available, electric power can be stored as needed while the vessel is underway and the onboard appliances left running overnight without having to turn on the engine, as shown in Fig. 11.

4.3. Market Reaction to Control Interface

The control interface and its ease-of-use received positive feedback, with users commenting on the ease with which operation could be switched from engine to electric motor drive and on the simplicity of being able to perform all control operations from the same display, with intuitive indication of the current operating mode. Another feature that particularly impressed users was how having an interface that worked at the touch of a selection button depicted by a mode icon made it easy to use under all conditions, even when the vessel was underway and the need to pay attention to the surroundings prevented the user from focusing on the screen. Fig. 12 shows an example of the screen being used.
The feedback also identified areas in need of improvement. While the system’s lithium-ion batteries can keep the onboard appliances running for extended periods, use of this feature prompted requests to be able to turn off the display because it was too bright when sleeping and for ways of minimizing unnecessary electric power use when staying on board for a long period of time. This led to the addition of a new mode for staying on board when moored that is selectable from the display and separate from the existing standby mode used prior to getting underway. As shown in Fig. 13, the new mode reduces system power consumption by 80% when in standby, putting equipment that is not needed when moored on idle or turning it off entirely so that it does not interfere with sleep or the enjoyment of time onboard.

5. Conclusions

This article has described the newly developed YF12e hybrid system for pleasure boats. This involved transforming an existing Yanmar-developed propulsion engine into a hybrid system through the addition of lithium-ion batteries, an electric motor, and an inverter.
Yanmar has also established comprehensive one-stop support for the boat-builder customers who purchase and install the hybrid system, including after-sales services that cover the electric motor, lithium-ion battery, and other new components.
In the future, Yanmar will continue commercializing electrified products designed to reduce environmental impacts and improve comfort.