Rudder
A Rudder is the primary steering device of a ship — a flat, hydrofoil-shaped surface mounted at the stern, usually behind the propeller, that is turned to deflect the flow of water and thereby turn the vessel. When the rudder is angled, the water flow (accelerated by the propeller) pushes the stern sideways, swinging the ship's head in the desired direction.
The rudder is moved by the steering gear (a powerful hydraulic system) in response to the helm or autopilot on the bridge. Its effectiveness depends on water flow past it, so a ship steers best with way on and with propeller wash over the rudder, and much less well at low speed — which is why tugs and bow thrusters assist manoeuvring in port. Rudder and steering-gear reliability are safety-critical (a steering failure in confined waters is dangerous), so they are subject to regular testing and survey. The rudder works in concert with the propeller and, for close-quarters handling, thrusters. It is fundamental to a ship's ability to steer and manoeuvre safely.
The rudder is how a ship steers, and because it works by deflecting propeller-driven water flow, it loses bite at low speed — which is why manoeuvring in port needs tugs and thrusters. Its steering gear is safety-critical, tested and surveyed, since a failure in confined waters is dangerous. The rudder is fundamental to controlling a ship's heading.
Why does a ship steer poorly at low speed?
The rudder works by deflecting water flow; with little way on and less propeller wash over it, its turning effect is weak, so tugs or thrusters assist.
What moves the rudder?
The steering gear — a powerful hydraulic system — responding to the helm or autopilot on the bridge.