Marine radar

[1] They are electronic navigation instruments that use a rotating antenna to sweep a narrow beam of microwaves around the water surface surrounding the ship to the horizon, detecting targets by microwaves reflected from them, generating a picture of the ship's surroundings on a display screen.

It allows a 'lookout' to be maintained, being one of the approved available means for compliance with Rule 5, keeping a proper lookout under the International Regulations for Preventing Collisions at Sea.

As required by COLREGS, all ships shall maintain a proper radar lookout if it is available on board to obtain early warning of risk of collision.

Radar plotting with the use of an EBL and VRM, or the ARPA should be used to determine the information of movement and the risk of collision of other ships in vicinity.

In commercial ships, radars are integrated into a full suite of marine instruments including chartplotters, sonar, two-way marine radio, satellite navigation (GNSS) receivers such as the US Global Positioning System (GPS), and emergency locators (SART).

Animation of typical rotating X band marine radar antenna on ship. It radiates a narrow vertical fan-shaped beam of microwaves perpendicular to the long axis of the antenna, horizontally out to the horizon. With each rotation the beam scans the surrounding surface. Any ships or obstructions reflect microwaves back to the antenna, displaying on the radar screen.
Commercial marine radar display. Land areas are shown in yellow, and vessel tracks are displayed with green "tails" on the screen