Autonomous Underwater Vehicles (AUVs) are core intelligent equipment for marine exploration, resource survey, underwater operations, and scientific research monitoring. As the power core of AUVs, underwater thrusters directly determine the navigation stability, operation accuracy, and overall service life of the equipment. Unlike ordinary marine propulsion devices, AUV thrusters operate for a long time in complex underwater environments characterized by high pressure, high humidity, high salinity, sediment accumulation, and marine biofouling. They also need to adapt to complex working conditions such as long-term hovering, variable-speed maneuvering, and continuous cruising, making them the most vulnerable and failure-prone precision core components of the entire vehicle.
In practical applications, most premature aging and failure of AUV thrusters are not caused by product quality defects, but by improper operation, inadequate antifouling and anti-corrosion protection, non-standard maintenance, and unreasonable environmental adaptation. The high cost of thruster repair and replacement, as well as the difficulty of disassembly and calibration, directly affect the operational efficiency and project cost of AUVs. Combining the exclusive operational characteristics of AUVs, this article elaborates on scientific methods to extend the service life of underwater thrusters from five dimensions: operating condition control, antifouling and anti-corrosion, regular maintenance, environmental adaptation, and idle storage, so as to avoid core wear and maximize the performance value of the equipment.
1. Standardize Operating Condition Control: Reduce Mechanical and Electrical Loss from the Source
Most of the hidden wear of AUV thrusters stems from non-standard operating habits and unreasonable working load. As brushless precision power equipment, their internal motors, bearings, drive shafts, and sealing structures are extremely sensitive to operating conditions. Rough operation will accelerate component fatigue and aging, significantly shortening the service life.
First, eliminate frequent start-stop and extreme acceleration/deceleration operations. Many operators frequently start and stop thrusters, instantly accelerate at full throttle, or stop and reverse suddenly to fine-tune the navigation route. Such high-frequency impacts cause sudden changes in motor current, and repeated alternating loads on drive shafts and bearings, leading to metal fatigue, increased bearing clearance, and motor coil strain. Compared with frequent start-stop, the operation mode of uniform cruising and smooth speed change can greatly reduce the load of the power system and minimize electrical and mechanical wear, which is the core operating principle for extending service life. Meanwhile, avoid long-term full-load and over-speed operation. Long-time high-speed navigation and heavy-duty operations of AUVs will lead to continuous high motor temperature and excessive internal temperature rise, accelerating the aging of insulation layers and increasing the risk of short circuits and burnout.
Second, reasonably control hovering and maneuvering conditions. When an AUV is hovering at a fixed point or fine-tuning its attitude, the thrusters operate at low speed and high load for a long time, which is prone to problems such as stagnant water flow, insufficient heat dissipation, and local heat accumulation. Long-term accumulation of these issues will damage the internal precision structure of the motor. In operation planning, the navigation logic can be optimized to reduce invalid hovering and frequent attitude adjustments, maintaining a stable and balanced working load for the thrusters. In addition, avoid high-risk waters with shallow water turbulence, dense reefs, and excessive debris to prevent the thruster blades from deforming due to impacts with sand and rocks, or motor stalling and overload failures caused by entanglement with fishing nets, seaweed, and sediment, so as to avoid physical damage and secondary wear from the source.
2. Strengthen Antifouling and Anti-Biofouling: Eliminate Hidden Continuous Wear
Marine biofouling and water pollutant deposition are the "invisible killers" of AUV thrusters during long-term underwater operations. Seaweed, shellfish, plankton, sediment, and impurities in seawater and freshwater continuously adhere to the surfaces of propeller blades, fairings, and motor housings, forming stubborn dirt and causing a series of chain wear problems. This is also the failure trigger most easily overlooked by operation and maintenance personnel.
Biofouling directly increases the navigation resistance of thrusters, destroys the hydraulic balance of propeller blades, leading to reduced propulsion efficiency and increased vehicle vibration. Long-term eccentric operation accelerates the wear of bearings and drive shafts. Meanwhile, thick dirt wraps around the motor heat dissipation structure, hindering convective heat dissipation by water flow, causing internal heat accumulation and excessive temperature, and accelerating the aging of sealing rubber rings and motor insulation layers. In addition, the long-term electrochemical effect of attachments and water accelerates the corrosion of metal components, laying hidden dangers for water leakage and short circuits.
Targeted maintenance solutions are divided into active protection and post-operation cleaning. For active protection, special marine antifouling coatings can be applied to the surfaces of thruster metal housings and propeller blades to inhibit the adhesion and growth of marine organisms. For AUVs operating in the open sea for a long time, an external simple filter protection structure can be equipped to reduce the approach of large-particle sediment and floating debris to the thrusters. For post-operation cleaning, the thrusters must be cleaned in a timely manner after each underwater operation. Use high-pressure fresh water to wash away residual sediment, scale, and plankton on propeller blades, gaps, and housings to prevent long-term solidification and adhesion of dirt, eliminating adhesion wear from the root cause.
3. Precise Anti-Corrosion Protection: Adapt to Complex Water Environment Wear
AUV operations cover various waters such as freshwater, brackish water, and high-salinity seawater. The high-salt and high-chloride ion environment of seawater causes strong electrochemical corrosion, resulting in irreversible damage to thruster metal housings, drive shafts, fasteners, and sealing interfaces. This is the core environmental factor leading to the premature scrapping of thrusters. Corrosion causes rust, pitting, and perforation of metal components, as well as deformation and water leakage of sealing surfaces, directly triggering fatal failures such as motor water ingress and transmission jamming.
Scientific anti-corrosion requires a combination of material protection and passive protection. In terms of materials, priority should be given to ensuring that core metal components of thrusters adopt marine anti-corrosion alloys, duplex stainless steel, and other chloride ion corrosion-resistant materials, avoiding the problems of easy rust and pitting of ordinary steel, and improving environmental adaptability at the hardware level. For passive protection, sacrificial anode blocks must be equipped for high-salinity seawater operation scenarios. Using the principle of preferential anode corrosion, it offsets water electrochemical corrosion and protects the thruster housing and precision metal components. Regularly check the loss status of anode blocks and replace them in a timely manner when the loss exceeds 50% to ensure continuous anti-corrosion effect.
Meanwhile, conduct post-operation anti-corrosion treatment: thoroughly rinse the entire vehicle with sufficient fresh water after seawater operations to remove residual salt stains on the surface, preventing salt crystal precipitation from continuously corroding metals and rubber seals. Regularly inspect the corrosion at sealing interfaces, screw gaps, and drive shaft connections of thrusters, clean rust spots in a timely manner, and apply anti-corrosion grease to block the spread of corrosion.
4. Regular Refined Maintenance: Troubleshoot Hidden Dangers and Delay Component Aging
AUV underwater thrusters are high-precision sealed equipment with complex internal structures, high disassembly difficulty, and strict calibration requirements. Minor component aging, insufficient lubrication, and sealing failure will gradually evolve into major failures. Regular refined maintenance is the key method to extend equipment service life and reduce failure probability, focusing on four core dimensions: sealing, lubrication, electrical system, and appearance.
First, sealing system maintenance. Thrusters are soaked in water and subjected to water pressure changes for a long time, and internal rubber sealing rings and oil seals are prone to aging, hardening, and loss of elasticity, which are the main causes of water ingress failures. The status of sealing components should be inspected regularly according to operation frequency. For high-frequency operation equipment, aged sealing accessories should be inspected and replaced every 3-6 months to prevent water vapor from penetrating into the cavity and causing corrosion damage to motors and bearings. Avoid scratching the sealing surface during disassembly and maintenance to ensure the overall waterproof sealing performance of the equipment.
Second, transmission system maintenance. Drive shafts and bearings are the core of power transmission. Long-term operation is prone to problems such as dry lubricating grease and mixing of sediment and sewage, leading to dry grinding, abnormal noise, and jamming. Special waterproof, high and low temperature resistant lubricating grease should be replaced regularly, and old and deteriorated grease should be cleaned to ensure the smooth operation of transmission components and reduce mechanical wear. Meanwhile, manually check the rotation smoothness of propeller blades, troubleshoot abnormal jamming, noise, and clearance issues, handle minor faults in advance, and avoid aggravated wear due to operation with faults.
Third, electrical system inspection. Regularly check the status of thruster lines, wiring terminals, and waterproof plugs, clean oxidation and rust spots, inspect whether the line sheaths are damaged and plugs are loose, and eliminate poor contact, short circuits, and electric leakage failures caused by humid environments. Monitor motor operating current and temperature data, compare with standard working condition parameters, and predict motor aging and performance attenuation in advance.
Fourth, appearance component inspection. Regularly check whether propeller blades have minor deformation, gaps, or impact damage. Slight blade imbalance will cause long-term vibration wear. Correct or replace problems in a timely manner to avoid chain mechanical failures.
5. Standardize Idle Storage: Avoid Hidden Aging During Static Placement
The wear of many AUV thrusters does not come from the operation process, but from improper long-term idle storage. Long-term static placement of equipment in damp, dusty conditions, with sealing parts under pressure and deformation, and natural oxidation of metals will cause hidden aging of components. Failures are very likely to occur when reactivated, greatly shortening the overall service life.
Before long-term idle storage of the equipment, complete thorough cleaning of the entire machine, remove all dirt, salt stains, and moisture, and ensure the thrusters are completely dry before warehousing. The storage environment should be dry, ventilated, and constant temperature, avoiding humid, exposed, and alternating high and low temperature environments to prevent accelerated aging of rubber sealing parts and oxidation and rust of metal components. Meanwhile, remove or relax the pressure on propeller blades to avoid long-term compression and deformation. Conduct regular (monthly) power-on idle tests to activate the internal structure of the motor and prevent component jamming and line damp failure.
The service life of AUV underwater thrusters does not corely depend on the basic quality of the equipment itself, but on the whole-process control of operating condition control, environmental protection, refined maintenance, and standard storage. The vast majority of premature wear and sudden failures are man-made avoidable problems caused by rough operation, biofouling, seawater corrosion, lack of maintenance, and improper storage.
Following the operation and maintenance principle of "Smooth working conditions to reduce load, antifouling and anti-corrosion to resist environment, refined maintenance to eliminate hidden dangers, standard storage to prevent aging", and implementing full-dimensional control from pre-operation protection, standard operation, post-operation maintenance to idle period storage, can not only completely avoid more than 90% of common failures, greatly reduce repair and replacement costs and downtime loss, but also effectively extend the service cycle of thrusters, ensure the stability, accuracy and sustainability of AUV underwater operations, and fully release the operational value of intelligent underwater equipment.
