Glossary Archive

The velocity at which a vessel moves relative to the water it is travelling through, excluding the effects of current or tidal flow. Speed through water refers to the rate at which a vessel progresses through the water itself, as opposed to its speed over the ground, which includes the influence of currents and tides....

Large buoys, generally more than 5 m in diameter, are distinguished on charts because their unusually large size renders them a potential hazard to navigation, even to large vessels. Superbuoys are also referred to as - ODAS [Ocean Data Acquisition System]. These buoys are often used in oceanographic research, environmental monitoring, and navigation assistance. Key...

Electronic navigation standards for commercial vessels less than 24m . Equipment meeting the requirements of this performance standard is accepted by the Maritime and Coastguard Agency as a suitable arrangement which satisfies the chart carriage requirements stipulated within SOLAS Chapter V/19 for vessels for which MGN 319 (as amended) applies. This standard is not accepted...

A narrow channel between shoals

The area around a vessel at anchor where it can safely swing with changes in wind or tide without risk of collision or grounding. Swinging room is a critical consideration for anchoring a vessel, as it refers to the circular space a boat requires to pivot around its anchor due to shifting winds, currents, or...

A large, lightweight, balloon-shaped sail used when sailing downwind, designed with identical halves to allow it to be flown on either side of the boat using a spinnaker pole. A symmetric spinnaker is a type of downwind sail commonly used on sailing yachts to maximise speed and efficiency when the wind is coming from behind...

A graphical representation of meteorological data over a specific area at a particular time, used to display weather patterns and conditions. A synoptic chart, also known as a weather chart, is an essential tool in marine navigation and meteorology, providing a comprehensive overview of atmospheric conditions. It is constructed using data collected from numerous observation...

The alignment of three celestial bodies—typically the Earth, Moon, and Sun—along a straight line, often resulting in phenomena such as tides, eclipses, or new and full moons. Syzygy refers to a specific astronomical alignment where three celestial bodies, most commonly the Earth, Moon, and Sun, are positioned in a straight line. This alignment occurs during...

Verb: To change the direction of a sailing vessel by turning its bow through the wind, allowing the wind to shift from one side of the sail to the other. Noun: The course or direction a sailing vessel takes relative to the wind, specifically when sailing at an angle to the wind. In sailing, "tack" is a...

The lower forward corner of a sail, where it is secured to the boat or rigging.  The tack of a sail is the point where the luff (leading edge) and the foot (bottom edge) meet, typically attached to the boat or rigging. On a mainsail, the tack is secured near the mast, while on a...