The ocean is a treasure trove of Earth's resources, a vital barrier for national security, and a frontier for humanity to explore the unknown. As the core power unit of various underwater equipment, underwater thrusters act as the "heart" for underwater navigation, operation and detection. Their performance directly determines the endurance, maneuverability, concealment and operational accuracy of underwater vehicles. Driven by the iterative upgrading of fluid mechanics, motor control, new materials and bionic engineering, underwater thrusters have evolved from traditional mechanical propulsion to higher efficiency, lower noise, miniaturization, intelligence and bionics. They are widely applied in marine scientific research, ocean engineering, national defense, military affairs, civil recreation and other fields, serving as core supporting equipment for deep-sea exploration and marine resource development. This paper systematically reviews the development history, mainstream technical types and application scenarios of underwater thrusters, and analyzes the current technical bottlenecks and future development trends.
I. Development History of Underwater Thrusters
The advancement of underwater propulsion technology has always centered on four core goals: improving propulsion efficiency, reducing operating noise, enhancing environmental adaptability and optimizing control precision. Its development can be divided into three stages: traditional mechanical propulsion, electrified integrated propulsion, and intelligent & bionic diversified propulsion.
(1) Traditional Mechanical Propulsion Stage (Before the mid-20th Century)
In the early days, large manned submarines and rudimentary underwater detection devices dominated underwater operation equipment, equipped mainly with mechanical propellers and wheeled propulsion structures. At this stage, the technical principles were simple. Power output was realized through mechanical transmission structures, which featured rugged construction and low manufacturing costs to meet basic underwater navigation demands. However, this technology had prominent drawbacks: low propulsion efficiency, excessive operating noise and severe cavitation at high speeds. These issues not only damaged equipment structures but also greatly impaired underwater detection accuracy. Such thrusters were bulky and poor in maneuverability, unable to adapt to refined operations in shallow waters, narrow waterways and complex seabed terrains. They were only applicable to large vessels and heavy submarines with extremely limited application scope.
(2) Electrified Integrated Propulsion Stage (Late 20th Century – Early 21st Century)
With rapid breakthroughs in motor technology, waterproof sealing technology and automatic control technology, underwater thrusters entered the electrification era, eliminating the defects of traditional mechanical transmission. Brushless DC motors gradually replaced brushed motors. Featuring no brush wear, long service life and stable power output, they extended the equipment lifespan by more than ten times. Combined with integrated waterproof cavity design, the thrusters could perfectly operate in deep-sea environments with high pressure and strong corrosion. Meanwhile, water jet propulsion technology matured gradually, solving the severe cavitation and high noise problems of conventional propellers. It boasted compact structure, flexible control and strong anti-interference capability, becoming the mainstream propulsion solution for small and medium-sized underwater equipment. During this period, thrusters achieved miniaturization and integration, compatible with ROVs, AUVs and small submersibles. This transformation drove underwater operations from crude navigation to refined detection and pinpoint tasks, with initial applications realized in civil ocean engineering and marine scientific research.
(3) Intelligent & Bionic Diversified Propulsion Stage (21st Century – Present)
Over the past decade, the integrated development of optimized fluid mechanics algorithms, bionic engineering, intelligent control and new materials has brought underwater propulsion technology into a diversified innovation phase. While traditional propeller and water jet propulsion technologies keep being optimized, new technologies such as shaftless propulsion, bionic propulsion and electromagnetic propulsion have been put into practical use. Bionic thrusters simulate the movement patterns of marine creatures including fish tail swinging, squid jetting and jellyfish floating. Breaking the maneuver limitations of traditional mechanical propulsion, they deliver outstanding flexibility, ultra-low noise and superior concealment, and can operate stably in narrow gaps and complex turbulent waters. Equipped with intelligent adaptive control technology, thrusters can automatically adjust power output according to water flow velocity, water depth pressure and operating posture, greatly improving adaptability to complex marine environments. Currently, high efficiency, low noise, intelligence and lightweight design have become the core development features of underwater thrusters. The global market continues to expand, reaching 4.8 billion US dollars in 2024, among which brushless motor-driven thrusters account for over 60% of the market share, with industrialization accelerating steadily.
II. Mainstream Technical Types and Characteristics of Underwater Thrusters
After decades of technological iteration, mainstream underwater thrusters used in industrialization and scientific research fall into four categories. They differ significantly in applicable scenarios, performance advantages and shortcomings, forming a mutually complementary technical landscape.
(1) Traditional Propeller Thrusters
As the most mature and widely used basic propulsion technology, traditional propeller thrusters generate thrust by driving blades to rotate and utilizing the reaction force of water flow. Their core strengths lie in simple structure, high reliability, low cost and strong power output, meeting the high thrust demands of large underwater equipment such as large submarines, manned submersibles and conventional ships. Nevertheless, they have inherent weaknesses: cavitation easily occurs during high-speed operation, causing vibration and noise along with low propulsion efficiency. Their control accuracy is poor at low speeds, making them unfit for high-end scenarios such as silent reconnaissance and refined detection. At present, performance improvements are mainly achieved by optimizing blade streamline shapes, upgrading materials and precisely regulating rotational speed.
(2) Water Jet Thrusters
Water jet thrusters draw in water via water pumps and eject it at high speed to generate propulsive force through reaction, serving as the mainstream technical solution for small and medium-sized underwater equipment. Compared with traditional propellers, they have remarkable advantages: no exposed rotating parts ensures high safety and strong anti-entanglement performance against seaweed and floating debris. They produce mild cavitation, low noise and higher propulsion efficiency, with rapid response in steering and speed regulation and excellent maneuverability, ideal for operations in shallow coastal and complex waters. They are widely applied to small and medium-sized unmanned underwater vehicles, underwater robots and diving boosters. The only limitation is insufficient high-thrust capacity, which restricts their use on heavy-duty large-scale underwater equipment.
(3) Shaftless Thrusters
Shaftless thrusters represent a new generation of high-efficiency integrated propulsion technology. Abandoning the conventional central transmission shaft, they integrate the driving motor around the blades, which are directly driven by an annular motor. This structure greatly reduces equipment size and weight and enhances sealing performance, completely eliminating failures caused by transmission shaft wear and water leakage, and improving overall reliability and service life. In addition, the shaftless design reduces water resistance, boosts propulsion efficiency and further cuts down noise and vibration. Featuring lightweight design, high integration and superior concealment, shaftless thrusters are suitable for small intelligent submersibles, precision detection robots and special operation equipment, and have become a key R&D focus in high-end civil and military fields.
(4) Bionic Thrusters
Bionic thrusters are cutting-edge research-oriented propulsion devices. Based on bionic fluid mechanics, they simulate the natural movement modes of marine organisms, mainly including fish swing propulsion, jellyfish undulation propulsion and squid pulse jet propulsion. Their greatest merits are extreme silence, superior maneuverability and strong environmental adaptability. Their movement conforms to natural underwater fluid laws without drastic water disturbance, delivering far better concealment than traditional mechanical propulsion. They can move flexibly in narrow spaces, complex turbulent waters and precise underwater environments. Currently, they are restricted by low thrust, limited endurance and high industrialization costs. Even so, they are irreplaceable in special scenarios such as military reconnaissance, polar scientific research and fine ecological observation, and will be a core development direction for high-end underwater propulsion technology in the future.
III. Multi-field Application Scenarios of Underwater Thrusters
With continuous technological maturity, underwater thrusters have expanded their application scope, covering four core sectors: marine scientific research and detection, ocean engineering, national defense & military, and civil recreation. They support the intelligent and efficient operation of various underwater tasks.
(1) Marine Scientific Research and Detection
Underwater thrusters provide core power for deep-sea exploration and marine environmental monitoring. ROVs and AUVs equipped with high-precision propulsion systems can dive to depths of several kilometers to carry out tasks including seabed mapping, hydrological parameter collection, deep-sea organism observation, water quality analysis and ocean current tracking. China's manned submersibles Jiaolong and Fendouzhe adopt optimized high-performance propulsion systems, realizing precise hovering, attitude control and pinpoint operation at a depth of 10,000 meters, providing crucial support for deep-sea geology research, marine ecological studies and polar exploration. Meanwhile, silent bionic thrusters minimize disturbance to marine creatures, facilitating long-term marine ecological monitoring and research on species habits.
(2) Ocean Engineering Operations
Underwater thrusters play an irreplaceable role in marine oil and gas exploitation, offshore wind power construction, subsea infrastructure maintenance and other engineering scenarios. Underwater robots equipped with propulsion systems undertake routine inspection, fault repair and maintenance for offshore drilling platforms, subsea pipelines, underwater valves and wind power pile foundations. The precisely controllable propulsion systems enable robots to hover steadily and position accurately in deep-sea high-pressure and complex flow environments, performing high-risk work such as welding, cutting, inspection and salvage instead of divers, which greatly reduces construction risks and operating costs. Statistics show that market demand for diving propulsion equipment in domestic ocean engineering keeps rising, reaching about 2,000 units in 2025 and expected to grow to 4,500 units by 2030. Offshore wind power construction has become the major growth driver.
(3) National Defense and Military
National defense and military sectors represent the high-end application field for underwater propulsion technology, which sets stringent requirements on noise reduction, concealment, stability and endurance. Traditional propeller propulsion and silent shaftless propulsion technologies are applied to military submarines and unmanned underwater vehicles for covert navigation, deep-sea lurking, sea area patrol and reconnaissance missions. Thanks to ultra-low noise, high maneuverability and low detectability, bionic thrusters are widely installed on small reconnaissance submersibles and underwater spy robots. These devices can infiltrate complex sea areas to conduct intelligence collection, enemy reconnaissance and target tracking, hardly being detected by sonar systems. In addition, high-thrust propulsion systems support long-endurance and long-distance navigation of large military submersibles, meeting the demands of sea defense, underwater combat and maritime security. This technology is a core pillar for the modernization of marine defense equipment.
(4) Civil Recreation and Special Operations
Lightweight and portable underwater propulsion devices have gained rapid popularity in civil fields, widely used in diving activities, underwater sightseeing, underwater rescue and aquaculture. Diver Propulsion Vehicles (DPV) help divers move faster underwater, save physical strength and extend the duration of diving and sightseeing, becoming common equipment for recreational diving and professional underwater rescue. In aquaculture, small silent thrusters regulate water flow and improve water circulation. For special operations such as underwater salvage, river dredging and swimming pool maintenance, small intelligent propulsion robots can efficiently complete cleaning, salvage and inspection work. In recent years, the domestic civil underwater propulsion market has achieved remarkable growth, with a market size approaching 5 billion RMB in 2024 and a compound annual growth rate of 15.3% from 2015 to 2024, showing huge industrial potential.
IV. Current Technical Bottlenecks
Despite remarkable leaps in underwater propulsion technology, multiple bottlenecks still restrict the sound development of the industry due to harsh marine environments and technical limitations. First, it is difficult to balance high efficiency and low noise. High-thrust devices generally generate loud noise and vibration, while silent bionic thrusters lack sufficient thrust and cannot satisfy the dual requirements of heavy load and high concealment. Second, adaptability to ultra-deep sea environments needs improvement. In conditions of extreme high pressure, strong corrosion and low temperature, the sealing performance, power stability and durability of thrusters are vulnerable, and their reliability for long-term deep-sea operations remains to be enhanced. Third, endurance is limited. Deficiencies in existing battery energy storage technology lead to short working hours for small and medium-sized thrusters, failing to support long-distance and long-duration deep-sea tasks. Fourth, intelligence level needs upgrading. When encountering complex ocean currents and sudden water flow disturbances, some thrusters respond slowly in attitude adjustment and dynamic power adaptation, resulting in insufficient stability during precision operations. Fifth, high-end technologies come with high industrialization costs. R&D and manufacturing costs of cutting-edge technologies including shaftless propulsion and bionic propulsion remain high, hindering large-scale popularization.
V. Prospects for Future Development Trends
Combined with technological evolution rules and market demands, underwater thrusters will continue to advance towards five major directions: integrated high efficiency & low noise, intelligent adaptability, integrated lightweight design, green and low-carbon performance, and industrialization of bionic technology.
First, integrated performance optimization. By adopting fluid mechanics simulation, new composite materials and upgraded motor algorithms, the conflict between high efficiency and low noise will be resolved. Cavitation and operating noise will be reduced, while thrust density and energy utilization will be improved to combine high thrust, low noise and long endurance. Second, intelligent control. Integrated with artificial intelligence, sensor perception and adaptive control technologies, thrusters will realize real-time perception of water flow, water depth and attitude, as well as dynamic adjustment, enhancing autonomous adaptability to complex marine environments and supporting unmanned and high-precision intelligent operations. Third, integrated and lightweight structure. Continuous optimization of shaftless propulsion and integrated structures will reduce equipment size and weight, and improve sealing reliability to meet the demand for miniaturized and micro-sized underwater intelligent equipment. Fourth, sustainable and long-duration energy supply. Combined with hydrogen energy, new lithium batteries, wireless energy storage and other technologies, the endurance of thrusters will be extended. Meanwhile, energy consumption structure will be optimized to cut power loss and marine pollution, complying with the concept of green marine development. Fifth, industrialization of cutting-edge technologies. Efforts will be made to lower the application costs of bionic propulsion, electromagnetic propulsion and other emerging technologies, promoting their transformation from laboratory research to large-scale industrialization and expanding their application in special operations, high-end detection and national defense sectors.
As the core power equipment for marine exploration and development, underwater thrusters witness the course of humanity's exploration into the deep ocean. From traditional mechanical propulsion to electrified integrated propulsion, and further to intelligent and diversified bionic propulsion, every technological breakthrough drives the upgrading of marine scientific research, ocean engineering, national defense and civil industries. With the accelerated global marine development and growing strategic value of the ocean, innovation in underwater propulsion technology has become increasingly critical. In the future, driven by in-depth integration of multiple disciplines, underwater thrusters will break through existing technical bottlenecks and achieve all-round upgrades in performance, intelligence and industrialization. They will serve as a core support for humanity to explore the deep sea, exploit marine resources and safeguard maritime security, and contribute to building a maritime power and the high-quality development of the global marine economy.
