What Steers a Boat?
- The helm is the actuating device for the steering system of the boat. Whether the helm is a tiller directly connected to the rudder of a sailboat, a wheel connected to the rudder by cables, a small stick-shaped "jog lever" or a steering oar, it is the interface between the human and the vessel.
The most common system, the wheel, is just like the steering wheel of a car. As you turn it, it uses a linkage system to move a device which changes the direction of the boat. - As the human changes the settings of the helm, there is a system that makes the vessel change directions. It may be a system of ropes or cables attached to a bell crank. It may be a system of hydraulic linkages or it may be an electronic "fly by wire" system.
Most recreational vessels use a cable system, with cables led through pulleys to the back of the boat where they are fastened to a special hinge called a bell crank, that looks like the letter "T." The cables are attached to the ends of the crossbar of the "T," which pivots at a point at its center. As one side of the crossbar is pulled, it pulls the long vertical part, which represents the rudder, to that side.
Hydraulic steering uses hydraulic rams, like pistons pushing on one side of the rudder or the other, and electronic systems move the rudder from side to side with a motor. - The rudder is the part on the back of the boat that moves from side to side to cause changes of direction.
The rudder works by changing the laminar flow on one side of the vessel, increasing drag on that side. As a result, the other side tends to overrun the side with the decreased flow and the vessel turns. Put simply, imagine a car where the brakes only work on the left side. If you step on the brakes, the car will pull to the left. If you don't turn the wheel to the right to correct it, they will cause the car to turn to the left. The rudder of a boat acts like those brakes; when turned to the left, the boat turns left. When turned to the right, the boat turns to the right.
Because the rudder acts so much like a brake, turning the rudder to "hard left" or "hard right" is part of the emergency stopping procedure for a ship or a boat. - Some boats don't have a rudder. The most common are boats powered by outboard motors--the motor is moved from side to side to change the direction of the propeller's thrust. Some large vessels are powered by "Z-drives", which act like an outboard motor, except that they can be rotated through 360 degrees for maneuverability.
Some boats are powered by "sweeps," like gondolas in Venice. The steering oar is "swept" from side to side to propel the gondola forward, or held steady into a turn to make the gondola change direction.
Rowed or paddled boats, and boats powered by water jets are steered by changes in the application of thrust to one side or the other. - Autopilot, colloquially called "Iron Mike," is a steering system that uses information from the vessel's gyrocompass or its Global Positioning System (GPS) receiver to maintain a specific course to a point.
As autopilots have become more sophisticated, mid-sea course changes can be managed by the autopilot. While autopilots can free a mariner for other tasks of navigation or watchkeeping, the autopilot is incapable of recognizing changing or dangerous conditions as they develop. Consequently, a human should be present even when Iron Mike is steering.
