Bow thrusters are kind of propellers, which are smaller in size and which help in better maneuverability of the ships at lower speeds. They are normally used for maneuvering the vessel near the coastal waters or while entering or leaving a port. Bow thrusters aid in assisting tug boats in berthing the ship without wasting time. This saves a lot of money for the shipping company because of lesser stay of the ships in the ports. Moreover, existence of bow thrusters on a vessel eradicates the need of two tugs while leaving and entering the port, and thus saves more money.
In general, bow thrusters are transverse thrusters placed at the forward and aft end of the ship. The thruster located in the forward end is known as the bow thruster and the one located in the aft is known as the stern thruster. The requirement for the number of thrusters to be fixed depends on the length of the ship.
Construction and Working of Bow Thrusters
The bow and stern thrusters are positioned in the through-and-through tunnels which open at both sides of the ship. There are two such tunnels – at forward and aft ends of the ship. The thruster takes suction from one side and throws it out at the other side of the ship, as a result moving the ship in the opposite direction. This can be operated in both the directions i.e. port to starboard and starboard to port. The bow thrusters are positioned below the water line of the ship. For this purpose, the bow thruster room should be examine for water accumulation at frequently intervals of time.
The bow and the stern thrusters can be electric driven or hydraulic driven or diesel driven. Though, the most commonly used are electric driven, as in hydraulic driven thrusters there occur many leakage issues. Also, with diesel driven bow thrusters, the amount of upkeep needed is more and every time before starting someone needs to go to the thruster room to inspect the thrusters.
Bow thruster consists of an electric motor which is mounted directly over the thruster using a worm gear arrangement. The motor operates at a continuous speed, and whenever there is a change needed in the thrust or direction, the controllable pitch blades are altered. These blades are moved and the pitch is changed with the aid of hydraulic oil which moves the hub on which the blades are fixed. As the thruster is of controllable pitch type, it can be run constantly, and when no thrust is needed the pitch can be made to zero.
The thruster is controlled from the bridge and the directions are given remotely. In circumstance of remote failure, a manual method for changing the pitch is delivered in the thruster room and can be operated from there.
- The insulation needs to be examined frequently and should be kept dry. This is done because bow thrusters are not used frequently and thus there are chances of damages by moisture. Moreover, because of the frequent idle state of the bow thrusters, there can be reduction in the insulation resistance especially in colder regions.
- The space heater is inspected for operational condition so that the insulation can be kept dry.
- The bearings of the motor and the links are to be lubricated every month.
- The condition of hydraulic oil is to be inspected every month for water in oil and samples should be sent for lab study for further checking.
- The thickness of the contactors is to be examined from time to time.
- Checks are to be made for any water leakages in the bow thruster room which is indication of seal leaking.
- The flexible coupling between the motor and thruster should also be inspected.
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- Better maneuverability at low speeds of the ship.
- Safety of the ship increases when berthing in bad weather.
- Saves money due to reduction of stay in port and less usage of tug boats.
- A very large induction motor is needed, which takes a lot of current and load, and thus large generator capacity is needed.
- Initial investment is high.
- Upkeep and repairs are costly when there is damage.