With the vigorous development of the marine economy, small ships with a length of no more than 15 meters and a power of less than 30 kilowatts have been increasingly widely used in fields such as fishery production, inland waterway shipping, tourism and sightseeing, and maritime rescue. The performance of their propulsion systems directly determines navigation efficiency, maneuverability, and operational costs. Under the general trend of ship electrification and green transformation, rim thruster, with their prominent advantages of compact structure, high efficiency and energy saving, and quietness and environmental protection, have gradually broken the monopoly of traditional fuel propulsion systems and conventional electric propulsion systems, becoming one of the optimal choices for the main propulsion systems of small ships, and injecting new vitality into the high-quality development of the small ship industry.

I. Analysis of Core Characteristics of rim thruster

rim thruster, also known as shaftless rim-driven electric thrusters, are a new type of propulsion device that highly integrates motors and propulsion components. Their core design abandons redundant components such as the shafting, gears, and sealed boxes of traditional propulsion systems, consisting only of rim-type motors, propellers, water-lubricated bearings, and energy-saving deflectors. This realizes the direct drive of the motor and the propeller, laying the foundation for its adaptation to small ships in terms of structure.

Compared with traditional propulsion systems, rim thruster have particularly prominent core characteristics: first, the shaftless design eliminates energy loss during transmission, greatly improving propulsion efficiency, and at the same time simplifying the overall structure, with lighter weight and smaller resistance, which meets the strict requirements of small ships for space and load capacity; second, the use of water-lubricated bearings instead of traditional mechanical seals not only avoids the reliability hazards caused by seal leakage, but also further reduces friction loss and maintenance costs; third, the absence of gear meshing structure effectively suppresses navigation noise and vibration, achieving a nearly silent navigation experience, taking into account environmental protection and riding comfort; fourth, the overall integrated streamlined design, with the coordinated optimization of the front guide vanes, deflectors and casing, further reduces navigation resistance and improves propulsion stability. In addition, rim thruster can achieve 360-degree full-revolution precise control, with flexible steering and rapid response, eliminating the need for additional steering gears and greatly simplifying the ship's control system.

II. Adaptation Advantages of rim thruster as Main Propulsion for Small Ships

The application scenarios of small ships are mostly concentrated in coastal waters, inland waterways, breeding areas, etc., with complex and changeable navigation environments. They have high requirements for the maneuverability, space adaptability, environmental protection and maintenance convenience of the propulsion system. The characteristics of rim thruster are highly consistent with the needs of small ships, and their main propulsion advantages are specifically reflected in the following aspects.

(1) Compact Structure, Adapting to the Limited Space of Small Ships

Small ships have narrow cabin capacity and tight space on the deck and inside the hull. The shafting, gearboxes and other components of traditional propulsion systems occupy a lot of space, which often squeezes cargo storage, equipment installation and personnel activity areas, and even restricts the overall design layout of the ship. rim thruster adopt a highly integrated design, with small size and flexible installation in multiple positions such as the stern and bottom of the ship, without occupying the core internal space of the ship. This not only facilitates the optimization of the overall layout of the hull, but also increases the effective use space for small ships, adapting to the structural characteristics of various small ships such as kayaks, small fishing boats, sightseeing boats, and small law enforcement boats. For example, when a torpedo-shaped small work boat adopts a rim-driven thruster, the thruster can be directly installed at the stern without occupying the internal space of the stern, facilitating the arrangement of other components such as the steering gear and greatly improving the ship's space utilization rate.

(2) Flexible Maneuverability, Adapting to Complex Navigation Environments

Small ships often need to navigate in complex waters such as narrow waterways, breeding areas, and ports and terminals, frequently facing operations such as steering, berthing, and precise positioning, which have high requirements for the maneuverability and response speed of the propulsion system. rim thruster can achieve 360-degree full-revolution precise control, quickly switch between navigation states such as forward, backward, and lateral movement, with precise steering and rapid response. They can complete complex operations such as lateral berthing and in-situ U-turn without adjusting the ship's course, effectively reducing the difficulty of crew operation and improving navigation safety. Compared with traditional propulsion systems, rim thruster have stronger adaptability in narrow waters and shallow draft areas. Their shallow draft design can avoid the propeller touching the underwater sludge or obstacles, reduce the loss of propulsion components, and are especially suitable for the regular navigation of small ships in inland shallow waters and coastal breeding areas.

(3) High Efficiency and Energy Saving, Conforming to the Trend of Green Transformation

Currently, under the guidance of the dual-carbon strategy, various regions have introduced emission restriction policies for non-road mobile machinery. The "Action Plan for the Development of the Green Intelligent Ship Industry (2024-2027)" clearly proposes that by 2025, the electrification ratio of inland and coastal small ships should reach 35%, and traditional fuel propulsion systems are facing the pressure of elimination and renewal. The shaftless transmission design of rim thruster eliminates transmission loss, and the propulsion efficiency is increased by 15%-20% compared with traditional fuel propulsion systems, and it also has obvious energy-saving advantages compared with conventional electric propulsion systems. At the same time, rim thruster can be perfectly adapted to electric systems, and when matched with marine lithium batteries, they have no exhaust emissions and no oil pollution, conforming to the green and environmental protection development needs of small ships. According to industry data, in 2024, the shipment volume of electric small marine propulsion systems in China accounted for 62.9%, exceeding traditional fuel models for the first time. As a high-end electric propulsion solution, rim thruster further promote the electrification transformation of small ships and reduce the operational costs of shipowners.

(4) Quiet and Reliable, Adapting to Diverse Application Scenarios

The application scenarios of small ships are diversified, among which tourist sightseeing ships, ecological research ships, fishery breeding ships, etc. have strict requirements for navigation noise. rim thruster have no gear meshing and no shafting vibration, with extremely low operating noise, which can achieve nearly silent navigation. This not only improves the riding experience of tourists, but also avoids disturbing aquatic organisms in breeding waters and observation objects in research areas, adapting to the navigation needs of ecologically sensitive areas. In addition, rim thruster have significantly fewer components, with a simple structure and high reliability. The water-lubricated bearings have strong corrosion resistance, which can effectively resist the corrosion of seawater and inland river sewage, reducing the failure rate; at the same time, frequent maintenance is not required, only regular inspection of the propeller and bearing status is needed, which greatly reduces the maintenance workload and maintenance costs. It adapts to the needs of small ship owners for the reliability and convenience of the propulsion system, and is especially suitable for individual fishermen who lack professional maintenance personnel.

III. Application Status and Cases of rim thruster in Small Ships

At present, the application of rim thruster in the field of small ships has gradually become popular. Many domestic enterprises have increased R&D investment, launched rim-driven thruster products suitable for small ships, and formed large-scale commercial applications. As a high-tech enterprise specializing in the R&D of rim thruster, Guangzhou Offshore Engineering has more than 100 related patents. Its small rim thruster are widely used in inland tourist ships, small law enforcement ships and other ships, and have been recognized by the market for their advantages of no leakage and low noise; the rim thruster launched by Tianjin Feibo Technology appeared at the Dubai International Boat Show. Its model suitable for small yachts has attracted the attention of customers from all over the world with its characteristics of high efficiency, energy saving, compactness and convenience, and has reached a number of cooperation intentions.

In specific application scenarios, after small tourist sightseeing ships are equipped with rim thruster, the navigation noise is significantly reduced, the tourist experience is greatly improved, and the energy-saving effect is obvious, with the operating cost reduced by about 20%; after small law enforcement ships adopt rim thruster, relying on the advantage of full-revolution control, they can quickly respond and accurately position in narrow waterways, improving law enforcement efficiency; after fishery breeding ships are equipped with rim thruster, the silent operation avoids disturbing breeding organisms, the shallow draft design adapts to the navigation in shallow waters of breeding areas, and the maintenance is convenient, reducing the operational burden of fishermen. In addition, in the overseas market, the export momentum of China's small rim thruster is strong, mainly exported to Southeast Asia, Africa and other regions, adapting to the needs of local small fishing ships and tourist ships. In 2024, China's export volume of small marine propulsion systems reached 148,000 units. As a high-end product, rim thruster are gradually opening up the international high-end market.

IV. Development Prospects of rim thruster as Main Propulsion for Small Ships

With the continuous development and technological upgrading of the small ship industry, rim thruster, as a new type of propulsion system adapting to the needs of small ships, will further consolidate their main propulsion position and have broad development prospects. From the policy level, the continuous advancement of national green shipping policies and the elimination and renewal of old fuel-powered small ships will bring huge market demand for rim thruster; from the technical level, the technological breakthroughs of domestic enterprises in permanent magnet synchronous motors, intelligent control modules and other fields will further improve the power density, energy-saving effect and intelligence level of rim thruster, adapt to more types of small ships, and at the same time reduce production costs, breaking the import monopoly of high-end products; from the market level, the application scenarios of small ships are constantly expanding, and the growing demand in fields such as tourism and sightseeing, maritime law enforcement, and ecological scientific research will further promote the popularization and application of rim thruster.

In the future, rim thruster will develop in the direction of miniaturization, intelligence and diversification: on the one hand, they will further optimize the structural design, launch products with smaller volume and lighter weight to adapt to the needs of micro small ships; on the other hand, they will integrate intelligent control technology to realize functions such as remote monitoring, fault self-diagnosis and precise power regulation, seamlessly connecting with the ship's intelligent navigation system to improve the intelligence level of navigation; at the same time, they will expand application scenarios, gradually covering various small ships such as small fishing boats, emergency rescue boats and private yachts, and become the mainstream choice of propulsion systems for small ships.

V. Conclusion

With core advantages such as compact structure, flexible maneuverability, high efficiency and energy saving, quietness and reliability, and convenient maintenance, rim thruster are highly consistent with the space needs, maneuverability needs, environmental protection needs and operational needs of small ships, and have irreplaceable competitiveness compared with traditional propulsion systems. Under the background of ship electrification and green transformation, rim thruster have achieved large-scale application in the field of small ships, becoming an important driving force for promoting the upgrading of the small ship industry. With the continuous progress of technology, continuous policy support and growing market demand, the position of rim thruster as the main propulsion for small ships will become more stable, and they will surely provide strong support for the green, efficient and high-quality development of the small ship industry.