Marine navigation blends science and engineering, experience, and art, to direct vessels, in water, to their destinations. It is more than simply determining present position, but "staying ahead of the vessel", using every source of information, considering non-geographic information such as weather and the vessel's capabilities, and communicating it to the crew. The navigational requirements for a small recreational boat in a lake are different than those of a cargo ship in a North Atlantic gale; a fishing boat navigates differently for salmon off Alaska and for scallops off Cape Cod; an aircraft carrier, a submarine, and a fast attack craft, while all military, have very different navigational needs.
Knowing one's current position, and plotting it on a navigational chart, is the most basic element. Some of the basic techniques include:
- Dead reckoning: calculating position based on the vessel's best estimated course and speed from a previously known point; usually uses compass information
- Celestial navigation: measuring the position of the Sun and starts, and converting these to positions using calculations and reference materials
- Radio navigation uses radio waves, primarily using hyperbolic navigation systems such as LORAN, but also direction-finding on known radio transmitters
- Radar navigation: distinct from the use of radar for collision avoidance, radar navigation uses radar to determine the range and bearing from one's own ship to known reference points
- Satellite navigation: uses Global Navigation Satellite Systems such as GPS, often supplemented with additional terrestrial or satellite correction signals
- Acoustic navigation: primarily for submarines or for fishing and mining vessels concerned with the seafloor, uses sonar and other correction techniques (e.g., temperature and salinity) to detect and take bearings on objects below the water.