Maritime
Navigation
Comprehensive guides to maritime navigation — from fundamental concepts like CPA and TCPA to advanced ECDIS operation, ARPA radar use, and COLREG compliance. Written by certified Master Mariners.
NAVIGATION TOPICS
Navigation Knowledge Base
Every key navigation concept explained with professional precision — from bridge instruments to collision avoidance regulations.
CPA
Closest Point of Approach — minimum distance between two vessels
TCPA
Time to Closest Point of Approach — when CPA will occur
ARPA
Automatic Radar Plotting Aid — radar target tracking system
ECDIS
Electronic Chart Display and Information System
AIS
Automatic Identification System — vessel transponder system
Radar
Radio Detection and Ranging — primary navigation instrument
Bridge Watchkeeping
STCW requirements for navigational watch
Heading
Direction the ship's bow is pointing
Course
Intended direction of travel over ground
Bearing
Horizontal angle to an object from north
True North
Geographic north pole direction reference
COLREG
International Regulations for Preventing Collisions at Sea
FAQ
Frequently Asked Questions
What are the basic navigation instruments on a ship?
The primary navigation instruments on a modern ship include the magnetic compass and gyrocompass, radar (ARPA), ECDIS (Electronic Chart Display and Information System), AIS transponder, GMDSS radio equipment, echo sounder, GPS receiver, and speed log. Under SOLAS, vessels of certain sizes must carry specific equipment depending on their trading area.
What is the COLREG?
COLREG stands for the International Regulations for Preventing Collisions at Sea, adopted by IMO in 1972. The rules establish obligations for vessels navigating on international waters to prevent collisions. COLREG contains 38 rules covering lights, shapes, sound signals, and conduct in various visibility conditions. Rule 5 (Lookout), Rule 6 (Safe Speed), Rule 7 (Risk of Collision), Rule 8 (Action to Avoid Collision), and Rule 16 (Action by Give-way Vessel) are among the most important.
How is CPA calculated?
CPA (Closest Point of Approach) is calculated using relative motion analysis. On radar, the Own Ship is stationary at the centre and target ships plot a relative motion line. The perpendicular distance from the origin (own ship) to the relative motion line gives the CPA distance. Time to CPA (TCPA) is calculated by dividing the distance along the relative motion line to the CPA point by the relative speed. Modern ARPA systems calculate CPA and TCPA automatically for all tracked targets.
What is ECDIS and when is it mandatory?
ECDIS (Electronic Chart Display and Information System) is an electronic navigation system that displays official Electronic Navigational Charts (ENCs) updated with real-time information. Under IMO amendments to SOLAS Chapter V, ECDIS became mandatory for new ships from 2012, with a phase-in schedule completing for existing vessels by 2018. Ships using ECDIS with up-to-date ENCs may dispense with paper charts.
What does a Bridge Watch Officer do?
An Officer of the Watch (OOW) on the bridge is responsible for the safe navigation of the vessel during their watch. Under STCW Chapter VIII, OOW duties include maintaining a proper lookout, monitoring the vessel's position and heading, managing traffic via ARPA/AIS, adjusting course and speed as necessary, communicating with VTS and other vessels, and maintaining the navigational logbook. The OOW must immediately call the Master if in doubt about any navigational situation.