As a core power component of equipment such as ships and underwater vehicles, rim thrusters are widely used in marine engineering, underwater exploration and other fields due to their advantages of compact structure, high propulsion efficiency, low vibration and noise, and low space occupancy. Its core structure is mainly composed of a rim-mounted motor, propeller, bearings (water-lubricated or oil-lubricated), energy-saving nozzle, sealing device and control system. It works in corrosive media such as seawater and sewage, and bears high load and high pressure for a long time, which is prone to component wear, corrosion, seal failure and other problems, directly affecting the navigation safety and propulsion efficiency of the equipment. Scientific and standardized maintenance is the key to extending the service life of rim thrusters, reducing the incidence of failures, and ensuring stable operation of equipment. Combined with its structural characteristics and operating conditions, this article sorts out the comprehensive maintenance process and core points.

I. Core Principles of Maintenance

The maintenance of rim thrusters shall follow the core principles of "prevention first, combination of prevention and treatment, hierarchical implementation, and standardized operation", focusing on three core objectives: first, preventing early failure of key components (bearings, seals, propellers, motors) and reducing the risk of sudden failures; second, maintaining the propulsion efficiency and maneuverability of the thruster to ensure that it meets the thrust and steering requirements under various operating conditions; third, extending the overall service life of the equipment and controlling operation and maintenance costs. At the same time, it is necessary to strictly follow the requirements of CCS "Rules for the Classification of Steel Sea-Going Ships", "Rules for the Construction of Steel Inland Waterway Ships" and the equipment manufacturer's technical manual, and it is strictly prohibited to operate irregularly or disassemble randomly to avoid secondary damage.

II. Daily Inspection and Maintenance (Daily/Per Voyage)

Daily inspection is the basis for timely detecting potential failures and preventing hidden dangers from expanding. It shall be carried out in stages before the thruster is started, during operation and after shutdown. Focus on checking the following contents, keep inspection records, and stop the machine immediately for investigation if any abnormality is found.

(1) Pre-Startup Inspection

- Visual Inspection: Check whether the surface of the thruster nozzle, rotating ring and propeller is damaged, deformed or cracked, and whether there are foreign objects such as aquatic plants, ropes and gravel wrapped or attached to ensure that there are no obvious obstacles affecting operation; Check whether the nozzle shell plate and reinforcement structure are intact without damage or deformation.

- Seal Inspection: Check whether there is leakage (seawater, lubricating oil) at the connection between the thruster and the hull, the motor seal and the bearing seal. The seals shall be free of aging, falling off and damage, ensuring that the static leakage is 0 and the dynamic leakage meets the design requirements (for oil-lubricated bearings).

- Electrical Inspection: Check whether the power supply lines and control lines are firmly connected without looseness, damage or aging; Check that the slip ring (if any) is in good contact without wear or ablation marks; Confirm that the motor shell protection meets the IP68 level requirements without water ingress or moisture; Check that the power supply of the monitoring and alarm system is normal and all indicators are displayed normally.

- Auxiliary Inspection: Check whether the lubricating water supply of the water-lubricated bearing is normal to ensure that the friction pair can form a complete lubricating water film; For oil-lubricated bearings, check the lubricating oil level and oil quality, which shall be free of emulsification, deterioration and impurities, and the oil temperature shall be within the normal range; Check whether the cathodic protection device (if any) is intact and the anode has no excessive loss.

(2) In-Operation Monitoring

- Operation Status Monitoring: Observe whether the thruster operates stably without abnormal vibration or abnormal noise (such as friction sound, impact sound, whistling sound); Monitor whether the thruster speed and thrust direction are normal, and the steering system (if any) is flexible to operate without jamming or lag, meeting the performance requirements of the main steering device.

- Parameter Monitoring: Real-time monitor the motor temperature and bearing temperature (water-lubricated, oil-lubricated, magnetic thrust bearings) to ensure that they do not exceed the design upper limit, and the temperature of the magnetic thrust bearing does not exceed the demagnetization temperature of the magnetic material; Monitor the motor current and voltage without overload or short-circuit signs. For motors above 50kW, focus on monitoring the insulation status without insulation alarm.

- Seal and Medium Monitoring: Continuously observe whether there is leakage at the seal, and no abnormal leakage of seawater or lubricating oil; Monitor the lubricating water flow of the water-lubricated bearing to ensure normal heat dissipation and avoid water-free lubrication or dry friction; Observe whether there are metal debris, seal fragments and other impurities in the discharged medium to judge the wear of internal components.

(3) Post-Shutdown Maintenance

- Cleaning Treatment: Timely remove marine organisms, sludge and foreign objects on the surface of the propeller, nozzle and rotating ring to avoid corrosion and increased resistance; Clean electrical interfaces and sealing surfaces to remove surface moisture and dust, preventing electrical short circuits and seal failure; The use of antifouling agents containing copper oxide is prohibited to avoid corrosion of metal components.

- Status Recheck: Recheck the status of seals, lines and bearings to confirm no looseness or damage; Supplement lubricating oil for oil-lubricated bearings and clean the lubricating water channel for water-lubricated bearings to ensure no blockage; Check the fixing of the propeller to prevent loosening, and ensure that the junction between the propeller blade and the rotating ring is smoothly transitioned without shoulders or fillets.

- Environmental Protection: If the thruster is shut down for a long time or in a harsh environment, anti-corrosion treatment (such as applying anti-corrosion coating) shall be carried out on metal components such as the propeller and rotating ring; Carry out moisture-proof and dust-proof wrapping on electrical components to avoid seawater erosion; Check the base support components to ensure firm connection without looseness or deformation.

III. Regular Maintenance (Hierarchical Implementation)

According to the operation time of the thruster and the severity of the operating conditions, it is divided into monthly, quarterly and annual maintenance. Focus on disassembling, inspecting, maintaining and replacing core components to ensure long-term stable operation of the equipment. The specific contents are as follows.

(1) Monthly Maintenance (200-300 Operating Hours)

- Bearing Maintenance: Check the wear of water-lubricated bearings, clean the lubricating water channel, check the performance of friction pair materials, and ensure that the wear rate meets the design requirements; Replace the lubricating oil for oil-lubricated bearings, clean the oil filter and oil cooler, check the wear of the sealing device, and ensure no leakage; Check the heat dissipation of the magnetic thrust bearing, clean the heat dissipation channel, and confirm no overheating marks.

- Propeller Inspection: Disassemble the propeller, check whether the propeller blades have wear, deformation, cracks or cavitation marks. If the wear is serious or cracks occur, repair or replace them in time; Check the fixing of the propeller blade and the rotating ring, reinforce loose fasteners, and set reliable anti-loosening and anti-corrosion measures; For welded propellers, check the welding parts for no detachment or cracks, meeting the requirements of non-destructive testing Zone A.

- Electrical System Inspection: Check the insulation performance of the motor winding, measure the insulation resistance to ensure it meets the specification requirements; Check the accuracy of the control module and sensors (speed, temperature, rudder angle), calibrate the monitoring and alarm system, and ensure that the fault monitoring and alarm functions are normal, focusing on checking the alarm functions of motor insulation, bearing temperature rise and alarm system power failure.

(2) Quarterly Maintenance (800-1000 Operating Hours)

- Seal System Maintenance: Replace aging and worn seals (sealing rings, gaskets), check the flatness of the sealing surface, grind and repair it to ensure sealing performance; Check the sealing device where the propulsion device passes through the hull structure to prevent seawater from entering the ship; Apply special sealant to the seal to enhance the sealing effect and avoid seawater erosion of internal components.

- Rotating Ring and Hub Inspection: Check the strength of the rotating ring for no deformation or cracks, and the strength check safety factor is not less than 6; For thrusters equipped with hubs, check the hub strength to ensure that it can effectively transmit thrust and support the weight of the propeller blades and rotor; Check the gap between the rotating ring and the stator. If the gap is too large or uneven, adjust it in time to avoid friction and wear, and check the fluid flow in the gap to ensure normal heat dissipation.

- Steering System Maintenance (if any): Check the wear of the steering gear and steering actuator, add grease to ensure flexible operation; Check the power equipment and pipelines of the steering system to ensure that no single fault affects the steering capacity. For passenger ships, ensure that the steering system can still work normally when any power equipment fails; Calibrate the rudder angle to ensure that the steering time meets the requirements of the competent authority, and the steering system can maintain the current rudder position when the thruster fails.

(3) Annual Maintenance (2000-2500 Operating Hours)

Annual maintenance is a comprehensive disassembly inspection and maintenance. The entire thruster shall be completely disassembled, and all core components shall be comprehensively inspected, maintained and replaced to ensure that the equipment restores the best performance, and the work shall be carried out in conjunction with product inspection requirements.

- Comprehensive Motor Inspection: Disassemble the rim-mounted motor, check whether the stator and rotor windings are ablated, aged or damaged, and clean the dust and oil on the surface of the windings; Check whether the rotor permanent magnet (if any) is demagnetized or fallen off, and the total bearing capacity of the magnetic thrust bearing and water-lubricated thrust bearing meets the operating conditions; Check the motor iron core for no looseness or deformation, re-tighten the connecting parts, and do a good job in insulation treatment to ensure that the motor temperature rise, overload and short-circuit performance meet the specification requirements.

- Replacement of Core Components: According to the wear of components, replace severely worn bearings, propellers and seals; Replace aging cables, sensors and control modules; Replace the anode of the cathodic protection device (if any) to ensure anti-corrosion effect; For propulsion devices above 1000kW, check the thickness of the stator protective layer to ensure it meets the requirements and carry out monitoring and alarm calibration.

- Nozzle Maintenance: Check the thickness of the nozzle shell plate, and the thickness of the outer shell plate shall not be less than 0.8 times that of the inner shell plate; Check the middle reinforcing ring of the inner shell plate, whose thickness shall not be less than 2 times that of the inner shell plate, and the reinforcing ring shall be free of damage or deformation; Check the longitudinal and annular partitions in the nozzle to ensure they are evenly arranged and free of damage, the thickness of the partitions is not less than that of the outer shell plate, and the holes of the partitions are normal; Carry out anti-corrosion treatment on the nozzle and repair the damaged coating.

- System Commissioning: After maintenance, carry out no-load test run and load test run, monitor the thruster speed, thrust, vibration, temperature and other parameters to ensure they meet the design requirements; Commission the steering system and monitoring and alarm system to ensure flexible operation and accurate alarm; For contra-rotating rim thrusters, ensure that each propulsion motor operates normally independently, meeting the control and protection requirements; If used as a side thruster, check the thrust direction, speed indication and various fault alarm functions to ensure they meet the specification requirements.

IV. Key Points of Special Fault Maintenance

During the operation of the rim thruster, problems such as vibration and abnormal noise, insufficient thrust, leakage and electrical faults are prone to occur. Targeted maintenance shall be carried out to avoid the expansion of faults. The specific faults and maintenance points are as follows.

(1) Vibration and Abnormal Noise Faults

Common Causes: Propeller wear, deformation or foreign object entanglement; Bearing wear, excessive clearance or insufficient lubrication; Friction between rotating ring and stator; Loose installation base of thruster; Uneven gap between propeller blade and nozzle.

Maintenance Points: Remove foreign objects from the propeller, repair or replace the worn or deformed propeller; Replace worn bearings, supplement lubricating medium (lubricating oil, lubricating water), and adjust bearing clearance; Check the gap between the rotating ring and the stator, adjust it to the design range, and repair the friction part; Reinforce the installation base and fasten the support components; Adjust the gap between the propeller blade and the nozzle to avoid abnormal noise and vibration caused by friction.

(2) Insufficient Thrust Faults

Common Causes: Severe propeller cavitation and wear; Insufficient motor power and aging windings; Bearing jamming and increased operation resistance; Poor lubrication and increased friction loss; Thruster idling (air entrainment); Excessive fluid friction loss in the gap.

Maintenance Points: Repair or replace the cavitated and worn propeller and optimize the propeller blade structure; Overhaul the motor, repair or replace the aging windings to ensure that the motor power meets the requirements; Disassemble the bearing, clean the jammed foreign objects, and replace the damaged bearing; Check the lubrication system, supplement the lubricating medium, and clean the lubrication channel; Adjust the installation position of the thruster, increase the distance from the water surface, remove the attachments on the ship bottom to avoid idling; Optimize the rim gap configuration to reduce friction loss torque and improve propulsion efficiency.

(3) Leakage Faults

Common Causes: Aging and damage of seals; Impurities and scratches on the sealing surface; Damage to the lubricating oil/water channel; Seal failure at the connection with the hull.

Maintenance Points: Replace aging and damaged seals, clean impurities on the sealing surface, and grind and repair scratches; Check the lubricating oil/water channel and repair the damaged part; Reinforce the sealing device at the connection with the hull and reapply sealant; For oil-lubricated bearings, check the dynamic leakage of the sealing device to ensure it meets the design requirements, and replace the seal assembly if necessary.

(4) Electrical Faults

Common Causes: Loose, damaged or aging lines; Motor water ingress and moisture; Sensor failure; Control module damage; Wear and poor contact of slip rings.

Maintenance Points: Replace damaged and aging lines and fasten loose connection points; Dry and insulate the motor with water ingress and moisture, and repair the damaged windings; Replace faulty sensors and control modules; Repair or replace worn slip rings to ensure good contact; Check the monitoring and alarm system, calibrate the fault alarm function to ensure it meets the specification requirements; Ensure that the motor shell protection level reaches IP68 to avoid re-water ingress and moisture.

V. Maintenance Safety Specifications

- Pre-Operation Preparation: Before maintenance, cut off all power supplies of the thruster and hang the sign "No Closing, Under Maintenance"; Dock the equipment in a safe area to ensure the hull is stable; Wear personal protective equipment (non-slip shoes, protective gloves, waterproof clothing, insulated tools). For underwater operations, professional diving equipment and monitors shall be equipped.

- Disassembly and Assembly: Disassemble and assemble the thruster in strict accordance with the manufacturer's technical manual. Violent disassembly and random changes to the installation position of components are strictly prohibited; Mark the disassembled components and store them classified to avoid confusion and damage; During assembly, ensure that the tightening torque of the connecting parts meets the requirements, the junction between the propeller blade and the rotating ring is smoothly transitioned, the bearings and seals are installed in place, and the gap is adjusted to the design range; The propeller contains strong magnets (such as neodymium iron boron), so extra care shall be taken during disassembly and assembly to avoid tool interference or damage to the magnetic components, and keep away from items susceptible to magnetic fields such as bank cards.

- Media and Materials: Use lubricating oil, sealant and anti-corrosion coating that meet the design requirements. The use of inferior and non-conforming materials is strictly prohibited; Lubricating oil and seals shall be properly stored to avoid pollution and aging; The use of antifouling agents containing copper oxide is prohibited to prevent corrosion of metal components; The anode of the cathodic protection device shall be made of materials that meet the requirements to ensure the anti-corrosion effect.

- Commissioning and Test Run: After maintenance and repair, first carry out no-load test run, and then carry out load test run after checking no abnormality; During the test run, closely monitor various parameters, stop the machine immediately for investigation if any abnormality is found, and it is strictly prohibited to operate with faults; Only after the test run is qualified can it be put into normal use, and the test run record shall be made at the same time.

- Recording and Archiving: Establish a maintenance account for rim thrusters, and record in detail the inspection time, maintenance content, fault conditions, maintenance measures, replaced components and other information; Sort out the account regularly and file it for future reference for maintenance and fault investigation, and provide complete operation and maintenance records in conjunction with product inspection work.

VI. Maintenance Misunderstandings and Notes

- Misunderstanding 1: Ignoring daily inspection and relying only on regular maintenance. Daily inspection can timely find small hidden dangers such as foreign object entanglement and slight leakage. Ignoring them is likely to lead to the expansion of hidden dangers, causing serious problems such as bearing wear and motor failure, and increasing maintenance costs.

- Misunderstanding 2: Randomly changing component specifications. The specifications of the core components of the rim thruster (bearings, seals, propellers, motors) must be consistent with the design requirements. Random replacement will lead to reduced propulsion efficiency, poor component matching, and even safety accidents. The welding materials and processes of welded propellers must be approved, and non-destructive testing must meet the requirements.

- Misunderstanding 3: Adding too much or too little lubricating medium. Adding too much lubricating oil/water will increase operation resistance and cause leakage, while adding too little will cause insufficient lubrication and component wear. It is necessary to add according to the manufacturer's requirements and check the oil quality and water level regularly.

- Notes: For thrusters that have been in corrosive environments such as seawater and sewage for a long time, the maintenance cycle shall be shortened and anti-corrosion treatment shall be strengthened; For rim thrusters used in underwater vehicles, additional inspection of pressure-resistant sealing performance shall be carried out to ensure no leakage in the deep-sea high-pressure environment; After shutdown in winter, drain the lubricating water and lubricating oil to prevent component freezing and cracking; Regularly check the base support components, conduct strength check in accordance with specifications, and ensure that the bearing capacity meets the requirements; Avoid the thruster being entangled with gravel, ropes and other foreign objects, and keep away from complex shoal environments to reduce component wear and fault risks.

VII. Conclusion

The maintenance of rim thrusters is a systematic and regular work. It is necessary to strictly follow the principles of "prevention first and hierarchical implementation" combined with its structural characteristics and operating conditions, implement the requirements of daily inspection, regular maintenance and special maintenance, standardize the operation process, and strengthen safety management. Through scientific and effective maintenance, it can not only extend the service life of the thruster and reduce the incidence of failures, but also ensure that it always maintains good propulsion efficiency and maneuverability, providing a strong guarantee for the safe and stable operation of equipment such as ships and underwater vehicles. At the same time, it is necessary to continuously pay attention to the technical upgrading of rim thrusters, optimize the maintenance plan combined with the characteristics of new structures (such as energy-saving improved rim thrusters), improve the operation and maintenance level, and adapt to the higher requirements of marine economic development for equipment reliability.