The echosounder is an important navigational aid although in the context of fisheries, it is more highly regarded as an aid to detecting fish. Similarly, sonar that has been developed to search for underwater targets can be used for navigation.
For the fishing industry, radar has proven an invaluable aid to navigation, particularly in areas affected by fog or restricted visibility. While navigating, the fishing vessel uses the radar to avoid collision with other vessels by a process known as radar plotting which takes into account the track of the "own vessel" to determine the true track of the other vessel. In modern radar this calculation is carried out automatically using inputs from the vessel's log and compass, known as Automatic Radar Plotting Assisted (ARPA) radar. The procedures used are laid down in the International Regulations for Preventing Collisions at Sea (COLREGS). During navigation, in restricted visibility or during darkness, vessels can navigate in restricted waters by radar using the echoes from buoys or landmasses to keep to safe water. During the fishing process, vessels use radar to measure the distance of other fishing vessels or fishing gear to ensure that they have sufficient sea room to set and haul their own gear. This is very critical in areas of high fishing density, which are usually areas in which fog or restricted visibility is likely to occur.
Recent years have witnessed a rapid development in electronic equipment to fix the position of a vessel while at sea. Early navigational equipment such as Radio Direction Finding, Console, Decca, Loran and Omega have one by one given way to more accurate and reliable position-finding equipment based on satellite. Modern navigational equipment seems to have reached the ultimate where the position of a fishing vessel can be measured to within 10 metres at all times with a high degree of reliability and precision. This has been attained by the introduction of the Global Positioning System (GPS).
In its simplest form, the GPS will show Latitude and Longitude and Course and Speed. In more sophisticated versions, the position of the vessel can be displayed on a monitor, with data from other sources shown in relation to the vessel. The most common of these types is the Electronic Chart Display and Information System (ECDIS). In this system the vessel position is shown against the background of a nautical chart. The direction and distances of various points on the chart can be measured and navigation made much easier. Other data can also be included and, for fishing purposes, underwater obstacles such as wrecks or rough ground can be displayed. In a similar fashion, the individual skipper can input good fishing grounds or favourite trawl tows.