Bow thruster — service
Servicing a bow thruster: anodes, propellers, greasing the legs, checking the power supply and clutches so manoeuvres stay reliable.
A bow thruster makes manoeuvring in harbour far easier, but as a submerged and rarely used device it needs regular servicing. The most common are electric drives with the motor inside and the gearbox in the bow tunnel (Sleipner/Side-Power, Vetus), and less often hydraulic ones. The service is best done at haul-out, when the tunnel is accessible and dry. Before any work on the mechanism, disconnect the power — a powerful motor can start and maim your hands.
Start by inspecting the tunnel and the propellers. Remove fouling from inside the tunnel and off the blades, because even a thin layer greatly reduces thrust and barnacles stop the propellers turning. Check that the blades are not chipped or cracked and that they sit firmly on their shafts. Many designs hold the propeller with a nut and split pin or a key — check those retainers, so the propeller cannot fall off underwater.
The bow thruster's sacrificial anode is small and wears fast, which makes it a commonly neglected item. Replace it once half its mass is gone, choosing the material to suit the water (zinc/aluminium in salt, magnesium in fresh). Without a working anode, the aluminium or bronze leg corrodes and the whole gearbox has to be replaced at high cost. Never paint or grease the anode's contact face.
The gearbox (the leg) needs its oil or grease checked, depending on the design. On models with an oil chamber, check the level and condition of the gear oil — a milky colour means water inside and worn shaft seals that have to be replaced. On grease-lubricated designs, grease the mechanism with the product the maker recommends. Turn the propellers by hand and feel for stiffness or play indicating worn bearings.
Check the drive and the coupling. On electric drives the power goes through a coupling with a rubber insert or dogs — a cracked insert causes snatching and a loss of thrust. Check the motor brushes if they are accessible, and the contactors/relays, which are often the reason the joystick gets no response. Clean and tighten the terminals, because the high starting currents heat loose connections and burn them out.
A bow thruster's supply is a high-current installation that has to be taken seriously. Check the condition and tightness of the heavy cables, the main fuse and the battery dedicated to the thruster, where one is fitted. Corroded or loose terminals cause voltage drops and weak thrust and, in the worst case, overheating and fire. Make sure the battery is charged and sound, because the thruster draws very high current in short bursts.
Once reassembled, test it. After launching, run the thruster briefly both ways, listening to it and watching the bow respond — remember that an electric drive must not be held on for more than a few tens of seconds, or the motor overheats. Check for unusual vibration or noise pointing to damaged propellers or bearings. Note the dates of anode and oil changes and of the coupling inspection, to keep the servicing regular.
Material prices — products and options
Indicative prices in EUR (incl. VAT), as of July 2026. Products widely available in Europe; prices depend on the shop, the pack size and consumption. The links lead to example shops that ship across the EU. Dollar amounts are converted at 1 EUR = 1.1622 USD (ECB, 7 September 2026) and rounded — treat them as a rough guide, not a price in a US shop. Imperial values in brackets are conversions of the metric figure.
Sacrificial anodes for bow thrusters
- Vetus — zinc anode for BOW gearboxes
original for the BOW 25–95 kgf series, zinc (salt water)€18–28 (≈$21–33) - Sleipner / Side-Power — anode for SE/SP thrusters
original anode for Side-Power gearboxes€20–35 (≈$23–41) - Quick — anode for BTQ thrusters
for Quick BTQ thrusters; zinc or aluminium€18–30 (≈$21–35) - Magnesium anode (fresh water)
Mg version for lakes and brackish water€15–28 (≈$17–33) (approx.)
Propellers, spare blades and split pins
- Vetus — propeller/blades for BOW thrusters
original plastic propeller or a set of blades€30–70 (≈$35–81) - Quick — propeller for BTQ thrusters
replaceable composite propeller€35–80 (≈$41–93) - A4 stainless split pins (set)
a set of split pins/pegs in 316 steel€6–14 (≈$7–16)
Gear oil / grease
- Quicksilver — High Performance gear oil
oil for marine drive gearboxes, 1 l (0.3 US gal)€14–22 (≈$16–26) - Vetus — grease for the thruster gearbox
the grease recommended for servicing the leg€10–18 (≈$12–21) - Waterproof marine grease (tube)
waterproof lithium grease for bearings€8–16 (≈$9–19)
Rubber insert / coupling and motor brushes
- Vetus — flexible coupling / rubber insert
the shear element protecting the drive, original€20–45 (≈$23–52) - Quick / Sleipner — thruster coupling
insert or coupling for Quick and Side-Power thrusters€25–55 (≈$29–64) - Carbon brushes for the thruster motor (pair)
a set of brushes for the electric motor€12–30 (≈$14–35)
Removing fouling and cleaning
- Yachticon / Star brite — fouling remover
gel/liquid for cleaning the underwater hull and the tunnel€12–25 (≈$14–29) - Brass / nylon brush
brush for cleaning the tunnel and the propeller€4–12 (≈$5–14)
Terminal protection and corrosion inhibitors
- Battery terminal grease / acid-free
grease protecting high-current terminals€6–14 (≈$7–16) - CRC / WD-40 Specialist — corrosion inhibitor
protective spray for connectors and metal€8–16 (≈$9–19)
Tools and safety gear
- Torque wrench
for tightening terminals and bolts to a torque€30–90 (≈$35–105) - Digital multimeter
measuring voltage and continuity in 12/24 V systems€15–50 (≈$17–58) - Protective gloves and safety goggles
hand and eye protection during the work€8–20 (≈$9–23)