Small wooden fishing vessels make poor radar targets and do not show up well on a larger vessel's radar screen. The smaller vessel carrying a radar reflector, designed to increase the strength of the target on the screen, can correct this. Marine radar is effectively a "line of sight" system whereby objects seen on a clear day, giving a reasonable radar echo and within the radar's display range will be seen on the radar screen. Conversely, objects which cannot been seen on a clear day will not bee seen on the radar (i.e. behind hills).
Radar can also be used in clear visibility for navigation or collision avoidance purposes. The range and bearing of objects or ships are very easily charted. This exercise is known as radar plotting and involves the calculation of the true course and speed of a target from the apparent course and speed observed on the radar. This differentiation was emphasized when early radars were involved in what was described as "radar assisted collisions". Approaching ships would make small course alterations and the apparent bearing would indicate that the ship would pass the other ship. In fact, the combined actions of the two ships brought them onto a collision course. On many radars plotting is now carried out automatically by ARPA (Advanced Radar Plotting Aid) so that the true courses and speed are shown on the radar screen.
Radar uses an electromagnetic pulse of 5cm wavelength to transmit a signal. If this signal is reflected off a ship or landmass, the signal is picked up by the antenna and displayed on a cathode-ray tube (CRT). In more modern equipment the display is now LCD. As described elsewhere, the display of a radar screen is often combined with other navigational equipment such as ECDIS and GPS.
Training syllabi for three levels of radar training are given in the FAO/ILO/IMO Document for Guidance on Training and Certification for Fishing Vessel Personnel.