Glossary Archive

An emergency device that responds to radar signals by transmitting a series of pulses to help rescuers locate a vessel or liferaft in distress.  A Search and Rescue Transponder (SART) is an essential piece of safety equipment used in maritime emergencies to assist in locating vessels, liferafts, or individuals in distress. When activated, a SART...

A location where tidal information is derived by applying corrections to data from a nearby Standard Port.  A secondary port is a coastal location where tidal predictions are calculated by referencing a nearby standard port, which has a full set of tidal data. Since not all ports have their own dedicated tidal observations, secondary ports...

Substitute or repeater flags allow messages with duplicate characters to be signalled without requiring multiple sets of flags.

Occasionally a light may not be visible through 360 degrees, or it may shine different colours depending on where it is viewed from. In this instance the arcs or sectors of visibility and colours will be shown on the chart by dotted lines and a description of the sector such as 'obscured', 'W' (white light),...

A maritime safety message broadcast over radio to convey important but non-urgent navigational or weather-related information. Sécurité is a term used in maritime communications, particularly over VHF radio, to preface messages that concern the safety of navigation or provide important weather warnings. It is part of the Global Maritime Distress and Safety System (GMDSS) and...

A signalling system used to convey information at a distance by means of visual signals, typically using flags or lights. Semaphore is a traditional method of communication that has been used in maritime contexts for centuries. It involves the use of flags or other visual indicators, such as lights or mechanical arms, to send messages...

A type of boat or ship designed to operate efficiently in both displacement and planing modes, offering a balance between speed and fuel efficiency. A semi-displacement vessel is a hybrid design that combines characteristics of displacement and planing hulls, allowing it to operate effectively across a range of speeds. Unlike a pure displacement hull, which...

Vertical movement of waves or swell against, for example, a harbour wall

The direction which a current flows in a body of water. In marine navigation, understanding the set of a current is crucial for plotting an accurate course. The set is always described in terms of the direction in which the water moves rather than the direction from which it originates. For example, if the current...

The process of securing a boat in a stationary position by deploying and embedding an anchor into the seabed. When a mariner 'sets anchor', they are ensuring that the anchor is deployed correctly and securely lodged in the seabed to prevent the vessel from drifting due to wind, currents, or tides. The process begins by...