The Effects of a Bow Thruster on a Ship's Speed

Bow Thruster Identification

• A bow thruster is a small propeller installed on the port and starboard sides of a boat. The thruster is typically placed at the bow, or front, of the boat within a hollow tunnel cut into the hull's sides, hidden from the outside water forces.
  
  

Thruster Function

• As a boat approaches a dock, the captain applies power to the bow thruster. The thruster controls the side to side motion of the boat. For example, a boat pulls up parallel to a dock. The bow thruster facing away from the dock activates, propelling the boat's bow toward the dock. The captain varies the thruster's speed as it slowly moves the boat closer. Once the boat reaches the dock, the captain shuts the thruster off.
  
  

Thrusters and Ship Speed

• Thrusters are not meant to activate during a ship's high speed travels. The thruster's small hidden tunnel placement does not negatively affect the ship's ability for gaining, or sustaining, high speeds in the open ocean. Bow thrusters function well at 2 knots or less, essentially at docking speed. Speeds of 2 to 5 knots, or more, affect the thruster's turning ability. The forward water moving across the hull's bow creates a current on either side of the boat, negating the thruster's water moving ability.
  
  

Bow and Stern Thruster Combinations

• Many larger ships use both bow and stern, or rear, thrusters. This combination provides precise control over ship docking. In fact, a tug boat is not necessary for maneuvering these ships into the docking area. The captain uses both bow and stern thrusters simultaneously, varying the speeds for a parallel parking maneuver. However, both thruster types must be used at slow speeds since their propelling action diminishes with more headway, or boat speed.
  
  

Thruster Considerations

• Use of a bow thruster, without the help of a stern thruster, requires attention from the captain. The captain must concentrate on manually angling the stern to the side of the dock instead of focusing on the movement of the bow. The bow thruster's power may cause the stern to move away from the dock due to the powerful bow movement. The captain must keep both bow and stern sides in control as the boat moves sideways.