DefinitionThe basic of Marine Navigation
The process of directing a watercraft to a destination in a safe and expeditious manner. From a known present position, a course is determined that avoids dangers, and on this course estimates are made of time schedules. The task is to periodically effect en route checks and to make required adjustments.
The method used will depend on the type of vessel and on its role or mission. The devices available range from a simple compass to a host of sophisticated electronic systems. In all cases, the navigator must plan and prepare by setting instruments in order and by checking for predictable current and tidal effects and hazards to navigation en route. This preparation includeshaving the latest correct charts and reviewing pertinent sections of sailing directions, light lists, and tide and current tables.
The methods used to fulfill the requirements of these phases come after one of the following broad categories of navigation: dead reckoning, piloting, celestial navigation, and electronic navigation. The first three categories have become somewhat standardized; the fourth category has been under constant and innovative development.
While the navigator is occupied primarily with courses, speeds, distances, and position determination, the safety of the craft is not to be neglected. Integrated navigation-conning systems have the basic function of helping reduce the number of accidents between ships by having the computer correlate most of the data available during crowded conditions and thus help unburden the navigator by presenting these data in more usable form for better and quicker decision making. The system generally includes a collision avoidance device plus a general-purpose computer. The computer receives inputs from navigation sensors and from ship propulsion and ship status stations. The integrated console is designed to optimize the human engineering aspects of ship control and navigation.
Collision avoidance systems (CAS), also known as automatic radar plotting aids (ARPA), of varying degrees of sophistication have been developed to reduce the work load of the navigator and eliminate human error. Typically, such a system consists of a digital computer that receives inputs from the ship’s radar, compass, and log, and determines and displays collision threats, and in some installations provides a recommended avoiding action.
Vessel traffic services (VTS) have been established in a number of heavily trafficked ports throughout the world in an attempt to reduce the number of collisions and strandings and safeguard the environment. Generally the service provides marine traffic management of an advisory nature, but in an especially hazardous situation it may be necessary for the VTS to exercise emergency control of vessel movements. See also Vessel traffic service.
Traffic-separation schemes have been established in a number of high-traffic density areas throughout the world, primarily to decrease the risk of collision at sea. A typical scheme consists of the establishment of parallel traffic lanes separated by an intervening buffer zone, analogous to a divided freeway on land.
An electronic chart displays on a video screen the same type of hydrographic information that mariners seek in a traditional nautical chart. Electronic charts integrated with a range of information, and with hardware and software that can process a hydrographic database to support decision making, are classified as electronic chart display and information systems (ECDIS). In addition to displaying a real-time picture of the vessel’s position in the waterway, an ECDIS manages navigational and piloting information (typically, vessel-route-monitoring, track-keeping, and track-planning information) to support navigational decision making.
There are a variety of intelligent systems deployed aboard automated ship’s bridges: piloting expert systems, engineering and vibration expert systems, neutral network systems for adaptive and intelligent steering control, and automated intelligent docking systems.
Integrated bridge systems are designed to allow the wheelhouse to function as the operational center for navigational and supervisory tasks aboard the ship. These bridges in many cases become ship’s operations centers, incorporating controls and monitors for all essential vessel functions, including navigation, engine control, and communications.