Bow Thruster also know as Tunnel Thruster

Bow Thruster

Bow thruster allow the vessel turn to port or starboard side, without using the main propulsion mechanism which requires some forward motion for turning。Bow thruster is a transversal propulsion device built into or mounted, either the bow or stern, of a ship or boat, to make it more maneuverable. Bow thruster is primarily used for docking, slow speed maneuvering, emergency steering and station keeping at zero or slow forward speed. Bow thrusters make docking easier, since they allow the captain to turn the vessel to port or starboard side, without using the main propulsion mechanism which requires some forward motion for turning.

Tunnel thruster

1.Marine vessels usually have one or more tunnels built into the bow, below the waterline order to improve manoeuvrability.An impeller in the tunnel can create thrust in either direction which makes the ship turn. Most tunnel thrusters are driven by electric motors, but some are hydraulically powered. These bow thrusters, also known as tunnel thrusters, may allow the ship to dock without the assistance of tugboats, saving the costs of such service. Ships equipped with tunnel thrusters typically have a sign marked above the waterline over each thruster on both sides

Depending on the type of vessel, the range of application for bow thrusters extends from brief docking and casting-off in ports with a limited number of operating hours every year up to continuous operation under extreme load conditions in demanding offshore applications with dynamic positioning. Allow the ship to dock without the assistance of tugboats, saving the costs of such service

Bow Thrusters can be powered by diesel engines, electric motors or hydraulic motors.

Electric motors are included optionally in the scope of supply. The prime mover can be connected either horizontally or vertically and thus incorporated optimally into the naval architectural design.

When fixed-pitch propellers are used, electric and hydraulic motors allow the direction of thrust to be reversed. An additional reversing gearbox is required if the thruster is powered by a diesel engine.

Thrust is the decisive criterion of a bow thruster. Therefore attaches great importance to an optimum propeller design that is individually adapted to the vessel geometry in each case. At the same time, the propeller design takes into account any special requirements in terms of noise level that are relevant for the application. A major parameter for the effectiveness of a bow thruster is the size of the gap between the tunnel and the propeller, which has reduced to a minimum on all models.

Advantages

•For extreme load conditions, e.g. in the offshore sector

•For continuous and short-time service

•Low noise emission

•Available with either fixed or controllable-pitch propellers

•Compact design due to horizontal, vertical or inclined arrangement of the power input flange

•Combinable with diesel, hydraulic or electric drive

Mark as a big cross in a red circle: (x).

Tunnel thrusters increase the vessel's resistance to forward motion through the water, but this can be mitigated through proper fairing aft of the tunnel aperture (see below photo). Ship operators should take care to prevent fouling of the tunnel and impeller, either through use of a protective grate or by cleaning. During vessel design, it is important to determine whether tunnel emergence above the water surface is commonplace in heavy seas. Tunnel emergence hurts thruster performance, and may damage the thruster and the hull around it.

Externally mounted bow thrusters Instead of a tunnel thruster, boats from 30 to 80 feet (9 to 24 m) in length may have an externally mounted bow thruster. As its name suggests, an external bow thruster is attached to the bow, making it suitable for boats where it is impossible or undesirable to install a tunnel thruster, due to hull shape or outfitting. Externally mounted bow thrusters have one or more propellers driven by a small reversible electric motor which provides thrust in either direction. The added control provided by a bow thruster helps the captain to avoid accidents while docking.

Waterjet bow thrustersA Waterjet thruster is a special type of bow thruster that utilizes a pumping device instead of a conventional propeller. The water is discharged through specially designed nozzles which increase the velocity of the exiting jet. Waterjets generally have the advantage of smaller hull penetrations for an equivalent size thruster. Additionally, the higher exit velocity of the discharged water increases the relative efficiency as speeds of advance, or currents, increase, as compared to standard tunnel thrusters. Some waterjet bow thrusters can be configured to provide forward and aft auxiliary propulsion, or even full 360 degree thrust.