Bow and stern thrusters are designed to be powerful, robust and low maintenance, but they operate under demanding conditions. Regular inspection and basic maintenance help prevent unexpected failures, maintain full thrust performance and extend the service life of the system. This article explains how to keep VETUS DC thrusters in reliable working conditions through practical, preventive care.
Thrusters are often used only for short periods during manoeuvring, which makes it easy to assume they do not require much attention. In practice, this is exactly why maintenance is so important. Thruster systems combine high electrical loads, moving mechanical parts and underwater components, all operating in a marine environment where moisture, (salt) and vibration are constant factors. Over time, electrical connections can corrode, batteries can lose capacity, motor brushes can wear and sacrificial anodes can be consumed. These issues usually develop gradually and remain unnoticed until the thruster suddenly delivers less power or fails completely. Regular maintenance helps identify small problems early and ensures the thruster is ready when it is needed most.
Before any work is carried out on a thruster system, electrical safety must be the first priority. Thrusters are connected to high-current batteries capable of delivering extremely high power. If cables remain connected during inspection or servicing, there is a real risk of short circuits, accidental activation or personal injury. For this reason, the thruster batteries should always be fully disconnected before maintenance begins. This simple step protects both the technician and the equipment.
Reliable electrical connections are essential for proper thruster performance. Over time, exposure to humidity, salt air and vibration can cause terminals, solenoids and cable connections to corrode or loosen. Even minor corrosion increases electrical resistance, which leads to voltage loss and heat buildup when the thruster is operated. This not only reduces thrust power but also accelerates wear on electrical components.
Regular inspection of all electrical connections between the battery, solenoids and thruster motor helps prevent these issues. Contacts should be cleaned carefully and protected with a corrosion-preventive product applied using a brush or cloth. Spray products should be avoided, as liquids can penetrate electrical components and interfere with contact surfaces or solenoids.
Thrusters place a very high demand on the electrical system and rely on batteries that can deliver large currents instantly. If a battery is undercharged, ageing or incorrectly sized, the voltage will drop sharply when the thruster is activated. This voltage drop reduces thrust power and places additional stress on solenoids and cables, increasing the risk of overheating or failure.
Checking battery voltage under load every couple of months provides valuable insight into system health. In a 12-volt system, voltage should remain close to nominal when the thruster is running. A significant drop indicates weak batteries, insufficient cable sizing or poor connections. Batteries that can no longer supply the required current should be replaced, and all cables and fuses must meet the specifications for the thruster installation.
Even correctly installed thruster systems require periodic checking of all mechanical and electrical fasteners. Vibrations from the engine, hull movement and temperature changes can cause nuts, bolts and terminals to loosen gradually. Loose connections increase resistance and can lead to overheating without visible signs.
After installation, power circuit connections should be checked shortly after commissioning and again after a few weeks of use. During regular operation, a visual and mechanical inspection every three months is recommended, always with the batteries disconnected. Once per year, it is good practice to loosen, clean and retighten each connection along the entire power circuit, from the battery to the thruster motor. This ensures consistent electrical contact and long-term reliability.
Inside the thruster motor, carbon brushes provide electrical contact with the commutator. These brushes wear naturally as part of normal operation. If brushes become too short or are unable to move freely in their guides, contact with the commutator becomes unreliable. This can result in reduced power, intermittent operation or failure in one direction.
At least once per year, motor brushes should be inspected. Each brush should move smoothly under spring pressure and make full contact with the commutator. Worn brushes should always be replaced as a complete set to ensure even performance. Brush guides should be clean and free of distortion so that the brushes can move without restriction.
Underwater thruster components are continuously exposed to galvanic corrosion caused by stray electrical currents in water. Without proper protection, metal parts such as the tailpiece and propeller shaft can deteriorate over time.
Sacrificial zinc anodes are designed to corrode instead of these critical components. The anode fitted to the thruster tailpiece should be inspected regularly and replaced at least once per year, or sooner if it is more than half consumed. At the same time, other underwater anodes on the vessel should be checked to ensure the entire system remains protected against corrosion.
This article is validated by: Mr. de Blieck, Marine Systems Engineer at VETUS
Mr. de Blieck is a Marine Systems Engineer at VETUS with extensive experience in electric thruster systems. Together with the multidisciplinary R&D team at VETUS, he contributes to the development of technically accurate and practical guidance aligned with real-world marine operating conditions. Close collaboration between specialists across different disciplines ensures the reliability and quality of VETUS documentation.
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