The Essential Guide to Bow Thruster Construction and Functionality

A bow thruster is a type of propeller-type system installed at the bow (front) and stern (known as a stern thruster) of a ship. These are smaller than a ship’s propeller and help the ship be more maneuverable at low speeds. The bow thruster ship is typically used when maneuvering ships near coastal waters or canals or when entering or exiting a port in bad currents or adverse winds. 

The bow thrusters help the tug boats to moor the ship, allowing the ship to spend less time in port, avoiding unnecessary time and, ultimately, money wasted. Having a bow thruster ship on a ship eliminates the need for two tugs for departure and entry, saving more money. Vessels are now equipped with both bow and stern thrusters and are independent of tugs when navigating within port boundaries (unless port regulations require the use of tugs).

Bow Thruster Installation 

Side thrusters are generally transverse thrusters installed in the channels at the forward and aft ends of a vessel. The thruster attached to the front end is called the bow thruster, and the thruster attached to the rear end is called the stern thruster. The number of engines installed depends on the length of the ship and the cargo capacity. Ship routes also play an important role, as many countries have local regulations that require the use of tugboats when entering and exiting port borders.

The following are Essential for the Installation of Side Thrusters: 

  1. The thruster room, also known as the bow thruster room, must be easily accessible to the ship’s crew from the open deck.
  2. Most ocean-going ships use electric motors. The engine is a heat-generating machine and must be installed in a dry and well-ventilated area.
  3. A high water bilge alarm is installed in the bow thruster room, and its display should be in the engine control room and on the bridge.
  4. The engine compartment must be well-lit.
  5. The room must have at least one lamp from an emergency light source.
  6. If multiple panels are installed, he should only operate the thruster from one panel at a time.

Bow Thruster Structure and Function

The bow and stern thrusters are installed in continuous tunnels on each side of the ship. There are two such tunnels, one at the front and one at the rear of the ship. The engine takes in air from one side of the ship and exhausts it to the other side of the ship, moving the ship in the opposite direction. It can be operated in both directions, port to starboard and starboard to port. Additionally, diesel-powered bow thrusters require more maintenance, and each time,, someone has to enter the bow thruster room before checkingchecking the bow thruster. The engines used are mostly her CPP engines. The direction of thrust can be changed by moving the propeller hub blades.

The Thruster Assembly Consists of following Components: 

  1. Electric motor with safety relay
  2. Flexible coupling between motor and thruster 
  3. Bracket and housing for electric motor 
  4. Connection flange and shaft 
  5. Motor housing seal 
  6. Tailpiece with shaft seal 
  7. Bearing 
  8. Propeller shaft 
  9. Zinc anode 
  10. Grid with bars at the both ends of the tunnel 

How the Bow Thruster Works 

The bow thruster consists of an electric motor mounted directly above the bow thruster using a worm gear arrangement. The engine operates at a very constant speed, and the rotor blades are adjusted at a controllable angle for attack whenever a change in thrust or direction is required. These blades move and change pitch using a hydraulic fluid that moves the hub to which the blades are attached. The engine is of a variable pitch type, allowing continuous operation, and the pitch can be reduced to zero when thrust is not required.

The bridge controls the engine, and instructions are given remotely. In the event of a remote failure, a manual pitch change method is provided in the engine compartment and can be operated from there. Normally, a hydraulic valve block is activated in the BT chamber to control the blade pitch and change the blade angle in an emergency.

Considerations When Operating The Side Thrusters 

  1. Make sure the engine is fully started , and the hydraulic lines are open before operating the thrusters.
  2. Do not operate the thruster above its rated load. Otherwise, the engine may stall.
  3. Gradually increase capacity and shift pitch. Avoid sudden changes in BT movement.
  4. Thrusters are considered starting devices under load. Please operate only when submerged in water.
  5. Before operating the engine, check for small craft, swimmers, boats, or tugs next to the engine tunnel.
  6. Never touch moving parts or a running electric motor.
  7. When installing multiple panels, ensure that the thruster is operated from only one panel at a time.

Bow Thruster Maintenance 

1. The insulation must be in place. Checked regularly and kept dry. This occurs because the bow thruster is not used frequently and is therefore at risk of damage due to moisture. In addition, the bow thruster is often idle, which can lead to a drop in insulation resistance, especially in cold regions.

2. The operating condition of the space heater is checked to ensure that the insulation remains dry.

3. Motor bearings and joints must be lubricated monthly.

4. The condition of the hydraulic fluid should be checked monthly for moisture in the oil, and samples should be sent to laboratory analysis for further testing.

5. The thickness of the contactor should be checked from time to time.

Major Maintenance of the Bow Thruster 

Major overhaul and maintenance of the bow and stern thrusters are performed in dry dock when the hull is out of the water, and the engine blades and tunnels are easily accessible. The following maintenance operations are typically performed in a dry dock.

  1. O-ring and seal ring replacement 
  2. Pinion shaft removal 
  3. Gear set inspection and maintenance/replacement 
  4. Bearing replacement 
  5. Blade repair, cleaning, and replacement 
  6. Hub inspection and replacement if necessary. Repair 
  7. Inspection and overhaul of oil distribution box (for propeller blade operation) 

Advantages Of Using Bow Thruster 

1. Improved maneuverability of the ship at low speeds.

2. Improves ship safety when entering a port during bad weather.

3. Save money by reducing port time and also reducing the use of tugs.

 Disadvantages Of Using A Bow Thruster 

1. A large induction motor is required, which requires a large amount of current and load, so a large generator capacity is required.

2. Initial investment is high.

3. Maintenance and repairs in case of damage are expensive.

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