In the field of marine power, outboard motors, as propulsion engines installed on the outer side of the hull (ship's side), are widely used in personal recreational boats, as well as in industries such as fishing, commercial operations, and government law enforcement, due to their advantages of high integration and simple installation and procurement. According to the energy source, outboard motors can be divided into fuel-powered outboard motors and outboard electric motors. Although traditional fuel-powered outboard motors once dominated, with the development of technology, outboard electric motors are emerging and showing unique value, especially in the application of small cargo ships.

I. Working Principle and Structure of Outboard Electric Motors

Outboard electric motors use recyclable storage batteries as the energy source. The core components include the motor, the storage battery, and the control circuit for controlling the motor speed. In addition, there are also the housing, the connecting body, and the suspension device. Some products are equipped with value-added components such as GPS chips and battery management circuits. According to the position of the motor, they can be divided into the lower-mounted motor type and the upper-mounted motor type.

Lower-mounted Motor Type: The motor is located at the lower part of the outboard motor, and the output shaft directly drives the propeller shaft to rotate. DC brushless motors are commonly used, which have a high energy conversion rate and low kinetic energy transmission loss. The design of the connecting body can minimize the water resistance coefficient. It has a simple structure, a low failure rate, and high reliability. However, limited by the lower space, the size of the motor is relatively small, and it is commonly used in outboard electric motors with a relatively small horsepower. For example, outboard motors below 8 horsepower of the German company Torqeedo adopt this structure.

Upper-mounted Motor Type: The motor is placed at the top of the outboard motor, and the kinetic energy is transmitted to the propeller through the transmission shaft in the gearbox. The structure of the gearbox is similar to that of traditional fuel-powered outboard motors. The advantage is that the motor is less restricted by space, and its volume can be relatively large, which is suitable for outboard motors with a larger horsepower. Torqeedo's 20, 40, and 80 horsepower outboard motors adopt this design. In addition, according to the different positions of the storage battery, there are also the built-in type and the external type. Small horsepower models mostly adopt the built-in battery type for the convenience of users; large horsepower models usually use external batteries due to the high demand for battery capacity.

II. Advantages of Applying Outboard Electric Motors to Small Cargo Ships

Significant Environmental Benefits: Small cargo ships operate frequently in inland rivers, lakes, and other waters. The exhaust gas and oil pollution emitted by traditional fuel-powered outboard motors will pollute the water body and the air. Outboard electric motors produce zero pollution during operation and have no exhaust gas emissions, which is of great significance for protecting water resources and the air. They are especially suitable for small cargo ships operating in waters near scenic areas and nature reserves with strict environmental protection requirements, helping to maintain the ecological environment. For example, in some lake areas where tourism is the main industry, small cargo ships using outboard electric motors to transport goods will not damage the local beautiful environment, ensuring the sustainable development of the tourism industry.

Low Operating Costs: In terms of energy costs, the daily charging cost is much lower than the cost of purchasing fuel. According to actual calculations, under the same voyage, the energy consumption cost of outboard electric motors is only one-third or even lower than that of fuel-powered outboard motors. Moreover, outboard electric motors have a simple structure, fewer rotating parts, high working reliability, and extremely low maintenance costs. There is no need to regularly replace engine oil, spark plugs, or check complex mechanical transmission components like fuel-powered outboard motors. Taking a small cargo ship with a relatively high usage frequency as an example, the annual cost of maintaining a fuel-powered outboard motor may be as high as several thousand yuan, while the maintenance cost of an outboard electric motor is negligible. Long-term use can significantly reduce operating costs.

Convenient Operation and Maintenance: The installation of outboard electric motors is relatively simple. Usually, it only needs to be hung on the outer side of the stern plate, and there is no need for a complex stern shaft alignment process. Ordinary users can complete the installation under simple guidance. In terms of operation, outboard electric motors are equipped with electric starters and digital control systems. They can be started by pressing a button, and can display real-time operation data. The speed regulation and steering control are flexible, and the operation advantages are obvious in narrow waters or in operation scenarios with frequent docking and departure. In terms of maintenance, due to its simple structure, the main maintenance work is to clean the propeller and check the connections of the motor and the controller. There is no need for professional technicians, and ordinary crew members can be competent after simple training.

High Safety: Fuel has the characteristics of being flammable and explosive. During the transportation process of small cargo ships, if the fuel is stored or used improperly, it is easy to cause safety accidents. Outboard electric motors use electricity and have no such risks, reducing the potential hazards of fire and explosion and ensuring the safety of the crew and the goods. The safety advantages of outboard electric motors are particularly prominent on some small cargo ships transporting flammable and explosive goods.

III. Current Challenges and Countermeasures

Insufficient Endurance: Currently, the battery endurance of outboard electric motors is limited. The models with relatively strong endurance generally have an endurance time of 2-3 hours at an economic speed, which is difficult to meet the needs of small cargo ships for long-time and long-distance operations. To solve this problem, on the one hand, the endurance can be improved by increasing the number of battery packs, but it is necessary to reasonably design the battery layout to avoid adding too much weight and affecting the ship's load capacity and navigation performance; on the other hand, developing new high-performance batteries, such as solid-state batteries, to increase the battery energy density and the endurance mileage is also a key development direction of the industry in the future. In addition, in the operation planning, charging stations can be reasonably set up on the routes frequently traveled by small cargo ships to facilitate the ships to replenish electricity on the way.

Relatively Small Power: At present, the maximum power of mass-produced outboard electric motors still lags behind that of traditional fuel-powered outboard motors, which limits their application on larger and heavily loaded small cargo ships. In response to this, motor manufacturing enterprises are constantly increasing their R&D investment and improving the power by improving the motor design and using new materials. For example, some outboard electric motor products launched by Guangdong Epropulsion Technology Co., Ltd. have an expanding power range and gradually meet the needs of small cargo ships with different cargo capacities. At the same time, in the ship design, according to the power characteristics of outboard electric motors, the hull structure and the load distribution can be optimized to improve the ship's propulsion efficiency and give full play to the performance of outboard electric motors.

High Purchase Cost: As a relatively high-end product, the initial purchase cost of outboard electric motors is higher than that of traditional fuel-powered outboard motors. This is mainly due to its advanced battery technology, motor technology, and R&D costs. However, considering the long-term operating costs, the advantages of outboard electric motors in terms of energy consumption and maintenance can make up for the gap in the purchase cost. To reduce the pressure of users' upfront investment, the government and relevant departments can introduce subsidy policies to encourage ship owners to buy outboard electric motors; financial institutions can also provide preferential loan programs to help ship owners relieve financial pressure. In addition, with the maturity of technology and the expansion of production scale, the cost of outboard electric motors is expected to be further reduced.

IV. Successful Cases and Application Prospects

In some areas with relatively developed inland waterway transportation, there have been successful cases of small cargo ships applying outboard electric motors. For example, an inland small cargo transportation company in a certain city replaced some of its small cargo ships with outboard electric motors of Guangdong Epropulsion Technology Co., Ltd. After a period of operation, not only was the pollution to the surrounding environment reduced, but also a large amount of operating funds were saved within half a year due to the reduced operating costs. Moreover, the operation convenience was improved, the working intensity of the crew was reduced, and the ship's attendance rate was increased.

Looking to the future, with the continuous innovation and breakthroughs in battery technology and motor technology, the application prospects of outboard electric motors in the field of small cargo ships are broad. Their advantages in environmental protection, economy, and safety will attract more ship owners to choose them, promoting the small cargo ship transportation industry to develop in the direction of greenness and high efficiency. While ensuring the transportation of goods, they will make greater contributions to protecting the ecological environment of water areas and become one of the mainstream power choices for small cargo ships.