VETUS Thruster Maintenance

Routine Maintenance

Because thrusters require little maintenance, they frequently get no maintenance, occasionally with disastrous consequences. Thrusters are electrical and mechanical machines with metal and plastic parts that need to be maintained and protected. Here are the basics:

Always disconnect the cables from the batteries before working on your thruster – these are powerful
batteries, devices and conductors that can injure you if proper care is not taken.

Don’t allow your thruster motor, solenoids, cables, and other conductors to become dirty or corroded. Inspect them regularly and take preventative action by cleaning and coating them with corrosion preventers. Do not use an anti-corrosion spray on the motor or solenoids – the spray may penetrate the devices and coat the contactors and brushes, disabling the device. Use brush- or cloth-applied anti-corrosion coatings in these locations.

Once every two months, check the voltage of the thruster power circuit when the thruster is operating. If your battery voltage in a 12-volt system is much lower than 13 volts when the thruster is not operating (or 26 volts for a 24-volt system) and there is more than a two volt drop from thruster on to thruster off, your battery is either undercharged, or more likely, worn out and in need of replacement. A weak battery will provide less power to the thruster, which you will notice. What you won’t notice is that the contactors in the solenoids are being burned out through prolonged arcing, and a replacement solenoid pack will soon be needed.

When replacing a thruster battery, VETUS recommends that you buy a battery as close as possible to the thruster, then make the connections with marine-grade power cables of the size recommended by VETUS for your thruster, protected by a correctly sized slow-blow fuse. Cabling and fuse recommendations are in the Installation and Operation Manual supplied with your thruster. This information is also available in the VETUS catalog and digital catalog.

Because electric thrusters operate at very high power and amperage, not only do their motors generate a lot of heat, but other points of high electrical resistance in the battery-to-thruster motor circuits will do the same. The most common points of high resistance are corroded, loose and poorly made connections in the power circuits, and such connection can become very, very hot. To avoid this potentially dangerous condition, it is essential that all power circuit connections are checked and maintained on a regular basis. A complete check of all connections must be made by a qualified and
experienced marine technician immediately after installation of the thruster system and then a repeat check should be made after two or three weeks of operation. High levels of vibration and temperature fluctuations are normal conditions on a boat, and this vibration, combined with expansion and contraction of metal components, leads to threaded connections (nuts, bolts, and screws) frequently working loose.

After these initial connection checks, and always with the battery disconnected, check the threaded connections on the thruster motor and solenoid no less frequently than once every three months. Loosen, clean, and re-tighten every nut, being careful to use a static wrench on the back nut and a turning nut on the front nut of each connection. Failure to do this may result in a terminal post being twisted out of the solenoids or motor, both being difficult or impossible to repair. Once a year, start at the positive terminal of the battery bank and work up to the thruster and then back to the battery, loosening, cleaning, and re-tightening every connection. Careful and sparing use of di-electric greases and thread locking compounds can also be helpful in creating and maintaining good threaded connections.

Make sure that every cabin and compartment in your boat has heat and smoke detectors
– it’s better to be safe than sorry.

Your electric thruster motor has four brushes or four pairs of brushes in the motor head. The brushes are made principally of carbon and convey electricity to the moving part of the motor called the armature. The brushes are spring loaded and push down on a rotating wheel of brass conductor bars called the commutator. Over time, the brushes wear away until they are no longer making good contact with the commutator. When that happens, the electric motor stops working, sometimes initially stopping in one direction but not the other. The rate of brush wear is highly variable from one motor to another and, of course, is also greatly affected by how much the boat and the thruster is used. At least once a year, remove the ventilation cover or access panels from the top of the thruster motor and inspect the brushes. To avoid cutting your fingers on the sharp metal components in the motor head, use a pair of needle-nose pliers to grasp the connector wire of each brush and gently pull the brush back a quarter of an inch (6 mm) and let it go. It should slide easily in its guide and be in good contact with the commutator. If that is not the case, undo the connector screw holding the brush wire to the motor and pull the brush out of its guides. If the brush is shortened so much that the top spring can no longer push it down into good contact with commutator, you will need to replace it and the other three brushes or brush sets. If the brush has plenty of length but is not sliding freely in its guides, the guides have probably become distorted through overheating. This can sometimes be corrected by a very small reduction of the brush cross sectional dimensions by flat sanding on very fine emery paper. Any substantial distortion of the brush guides will require repair or replacement of the motor. When you are ready to reinstall the brushes, make a small hook from coat-hanger wire or similar and use that hook to gently pull the brush spring out of the way to allow the brush to enter its guides. Then, using the hook, position the pusher face of the spring on the brush head.

And last, but by no means least, replace the protective zinc anode on the outside of the thruster tailpiece (the bronze gearbox that is located underwater in the thruster tube) at least once a year. This chunk of zinc is intended to be eaten away by electrolysis, and if it’s not there, or is much reduced, your tailpiece, including the inner sections of the thruster prop shaft, will be eaten away be electrolysis instead of the zinc. Sometimes this can happen very quickly if there is stray current in the water around your boat, either from your boat, another boat, or the marina electrical system. The rate of erosion of the zinc anode is also accelerated in warm water. The zinc on your VETUS thruster is bolted to the bottom of the bronze tailpiece or fastened to the end plate of the tailpiece as a collar behind the prop or, on larger thrusters, forms the boss on the propeller hub and is attached to the shaft of the thruster prop shaft. If you are swimming, snorkeling, or diving around the boat when it’s anchored in clear water, take the opportunity to inspect all the zincs (they’re also on the propulsion shafts and other underwater metal equipment). Even if it’s not time for your annual haul out, if a zinc is more than half gone, it needs to be replaced. Replacing the equipment, a zinc is protecting is going to cost you a lot more than having a diver install a new zinc or even hauling the boat for a day to replace a zinc.

Those are the basics – keep your boat well maintained and safe!