Marine navigation is the science and skill of finding a safe path across water. Ships and submarines must know their position, direction, speed, and nearby hazards even when land is not visible. Modern navigators combine electronic systems with older tools such as charts and compasses because the ocean is constantly changing.
Good navigation protects people, cargo, ecosystems, and coastlines from accidents.
Key Facts
- Speed at sea is often measured in knots, where 1 knot = 1 nautical mile per hour.
- 1 nautical mile = 1852 m, which is based on latitude on Earth.
- Distance = speed x time, so d = vt can be used for voyage planning.
- Course is the intended direction of travel, while heading is the direction the vessel is actually pointed.
- GPS position is found by timing radio signals from multiple satellites.
- Radar estimates distance using wave travel time: distance = ct/2, where c is wave speed and t is round-trip time.
Vocabulary
- GPS
- GPS is a satellite navigation system that calculates position from the timing of radio signals sent by satellites.
- Radar
- Radar is a system that sends radio waves and detects their echoes to locate ships, land, storms, and obstacles.
- Nautical Chart
- A nautical chart is a map for marine navigation that shows coastlines, depths, hazards, buoys, and navigation routes.
- AIS
- AIS is the Automatic Identification System, which lets ships broadcast their identity, position, course, and speed to nearby vessels and shore stations.
- Inertial Navigation
- Inertial navigation estimates position by measuring acceleration and rotation, which is especially useful for submarines underwater.
Common Mistakes to Avoid
- Treating GPS as always perfect. GPS signals can be blocked, jammed, reflected, or unavailable, so navigators must compare it with radar, charts, compass readings, and visual observations.
- Confusing heading with course. Heading is where the bow points, but wind, waves, and currents can make the actual path over the ground different.
- Ignoring chart depth information. A route that looks short on a map may cross shallow water, reefs, restricted areas, or underwater hazards.
- Assuming submarines can use GPS while deep underwater. GPS radio signals do not penetrate seawater well, so submarines rely on inertial navigation, sonar, depth sensors, and occasional updates near the surface.
Practice Questions
- 1 A ship travels at 18 knots for 4 hours. How many nautical miles does it travel?
- 2 A radar pulse returns from a target after 0.00008 s. Using c = 3.0 x 10^8 m/s, how far away is the target?
- 3 A submarine is underwater and cannot receive GPS. Explain how it could still estimate its position and why errors may grow over time.