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Bow Thrusters

What is a Thruster?

In order to increase the maneuverability at low speeds modern day ships come with a device built into, or mounted to either the bow or stern, of the ship this transversal propulsion device is called a thruster. The use of thruster allows the vessel to be more maneuverable while travelling at a slow speed, this in turn helps the vessel to move through narrow canals, coastal waters, docking etc. Thrusters are mainly of two types i.e. Bow Thrusters (fitted in the forward part of the ship) and Stern Thrusters (fitted in the back or the stern part of the ship) which although have different applications but primarily have the same function of providing stable maneuverability of the ship.

Bow Thruster

A bow thruster, as discussed earlier, is a type of thruster that is fitted on the bow of the ship, whose main function is to navigate the ship through coastal areas, canals or entering or leaving a port, or overall maintaining the stability of the ship during adverse weather conditions.

Bow Thrusters
Bow Thrusters

Construction and Working Mechanism of a Bow Thrusters

A thruster system generally consists of the following constituents-

  • Electric Motor with safety relays
  • Coupling between motor and thrusters
  • Mounting and casing for the motor
  • Connecting flange and shaft
  • Motor casing seal
  • Tailpiece
  • Bearings
  • Propeller shaft
  • Zinc Anodes
  • Grid bars on either side of the tunnel

The thruster is placed between an open-ended tunnel in the bow or stern end of the ship. In simple words, these thrusters take suction from one side of the ship and eject out of the other side, causing the ship to move in the opposite direction.
          The thrusters can be operated hydraulically, electrically or by diesel. These days, electric thrusters are most widely used because the other two, (hydraulic and diesel-driven) are prone to leakage and other complications. Thrusters are also designed in a way such that the propeller boss can be moved and various angles can be made in order to provide a wide range of angles, hence better precision while travelling at low speeds.
          The electric motor is mounted directly above the bow thruster. It runs at a constant speed and is connected to the propeller using a worm gear arrangement, such that the angle between the blades can be easily adjusted. Any required change in the direction or thrust can be remotely controlled. Even when not in use, the pitch of the blades can be made zero.

Types of Bow Thrusters

On the basis of design, bow thrusters are mainly of three types:

Lateral or Tunnel Thrusters- In this type of bow thrusters system, the impeller or propeller is fixed and immovable and are placed in a tunnel in the bow side of the ship. Although they provide better maneuverability for the ship, they can sometimes cause resistance and thereby affect the efficiency. Also, they require a lot of power to operate which in turn increases the fuel consumption as well. Overall, it is a good type of thruster mechanism, with its fair share of pros and cons.

Lateral or Tunnel Bow Thruster
Lateral or Tunnel Thruster

Jet Thruster In this type of Bow thrusters a jet is fitted in the bow of the ship, which uses suction from the keel and discharges it to either side of the bow. It is a simple and lightweight system and is used in smaller vessels. It consists of a powerful centrifugal pump instead of a propeller/impeller, which is fitted to a three-way valve and electrical controls.

Jet Bow Thruster
Jet Thruster

Azimuth Thruster In this type of Bow thrusters the propeller itself is able to move in any horizontal angle. This not only provides excellent controlled maneuverability; it also is competent enough to replace the traditional ‘Propeller-Rudder’ system. It is highly efficient, in terms of power consumption and ship-space usage. It also does not require any sort of tugboats. But on the other hand, it increases the drought of the ship. It also requires a special pilot training to work with one of these.

Azimuth  Bow Thruster
Azimuth Thruster

Functions and Applications

These are basically propeller-shaped systems that are attached to the front or bow of the ship. Although they are smaller in size in comparison to the Ship’s main propeller, these play a very crucial role in better, more precise maneuvering of the ship. The main function of a bow thruster is to make the ship capable enough to make precise movements and get more and more independent from tugboats or tugs. It can also increase speed of the vessel while reducing the fuel consumption. Some steerable thrusters these days are also capable of replacing rudders and thereby optimizing the ship-space and reducing manufacturing and maintenance costs.

In modern times when shipping plays such a significant role in the world economy, it is required to make our ships more technologically sound, so as to not only increase the efficiency but also keep the costs to a minimum. Which is why it is important to be wise and understand which type of thrusters are required to match the requirements of the ship. Tugboats are now obsolete and better control over the navigation of a ship is of supreme importance when moving through narrow waters, canals and coastal regions.

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