KUP 6: Have knowledge of the principles of magnetic and gyro-compasses
Learning objective:
In this KUP, learners will gain a foundational understanding of the principles behind both magnetic and gyro-compasses, essential navigation tools in maritime operations. The objective is to familiarize learners with how these compasses function, their differences, and their practical applications on board a vessel. By the end of this section, learners will be able to explain the core mechanisms that allow each compass type to determine direction, recognize factors that influence their accuracy, and apply this knowledge in real-world navigational scenarios.
Learning content:
1. Gyro-compass
A gyro compass is a device that uses a spinning wheel (called a gyroscope) to maintain its orientation towards the true north pole1.
A gyroscope has two properties: gyroscopic inertia and precession.
- Gyroscopic inertia means that a spinning wheel tends to keep its plane of rotation constant unless an external force acts on it.
- Precession means that when an external force (such as gravity or torque) acts on a spinning wheel, it causes it to move at right angles to both the axis of rotation and the applied force.
A gyro compass uses these properties and two natural forces: gravity and Earth’s rotation, to align itself with true north. The gyroscope is mounted in such a way that it can tilt freely about three perpendicular axes: horizontal, vertical and spin axis. When power is applied, the gyroscope spins rapidly about its spin axis (usually several thousand revolutions per minute). As it spins, gravity pulls down on its horizontal axis, causing it to tilt slightly downwards.
At this point, Earth’s rotation comes into play. As Earth rotates from west to east at about 15 degrees per hour (360 degrees per day), it exerts a torque on the tilted gyroscope, causing it to precess clockwise about its vertical axis (when viewed from above). This precession makes the gyroscope gradually align its spin axis with Earth’s rotational axis (which points towards true north).
Once aligned, the gyro compass sends electrical signals to repeater compasses located throughout the ship, which display the true heading. The gyro compass also feeds data to other navigational instruments such as autopilot, radar, and GPS.
2. Magnetic compass
Magnetic compass, in navigation or surveying, an instrument for determining direction on the surface of Earth by means of a magnetic pointer that aligns itself with Earth’s magnetic field. The magnetic compass is the oldest and most familiar type of compass and is used in different forms in aircraft, ships, and land vehicles and by surveyors.
Recommendation:
1. Handbook of Magnetic compass
2. Gyro compass technical book
Reference:
1. Navigation. Ding Yong. Publisher: People’s Communications Press.