Glossary Archive

A scientific institution operated by the United States Navy that specialises in astronomical and timekeeping research, providing precise navigational data for military and civilian use.  The United States Naval Observatory (USNO) is one of the oldest scientific agencies in the United States, established in 1830 to support naval navigation by producing accurate astronomical data. It...

The primary time standard by which the world regulates clocks and time serving as the basis for civil time globally. Coordinated Universal Time (UTC) is the internationally recognised time standard that ensures uniformity in timekeeping across the globe. It is not a time zone but rather a reference point from which all time zones are...

Ultraviolet (UV) light is a type of electromagnetic radiation with a wavelength shorter than visible light but longer than X-rays. In the marine context, UV radiation from the sun can have various effects on the marine environment, including damaging coral reefs, affecting marine organisms, and degrading marine materials exposed to sunlight. UV radiation is also...

A line or tackle system used to control the angle of a boom on a sailing vessel, preventing it from lifting and stabilising the sail. The vang, also known as a boom vang, is an essential piece of rigging on a sailboat that helps manage the shape and performance of the mainsail. It typically consists...

The maximum angle of heel at which a vessel can recover to an upright position without capsizing. The vanishing angle is a critical concept in naval architecture and marine safety, referring to the point beyond which a vessel loses its ability to right itself and becomes unstable, leading to capsizing. This angle is determined by...

The angular difference between true north and magnetic north, also known as magnetic declination, which affects compass readings. Variation is a crucial concept in marine navigation, as it accounts for the difference between true north (the direction along the Earth's surface towards the geographic North Pole) and magnetic north (the direction a magnetic compass points,...

The International Maritime Signal Flag Victor. Meaning I require assistance.If appended with a Numeral Pennant, Velocity in kilometres per hour.

A measure used in satellite navigation systems, such as GPS, to quantify the impact of satellite geometry on vertical positioning accuracy. It indicates how well-positioned satellites are in relation to one another in the sky. A lower VDOP value indicates better satellite geometry and, therefore, higher accuracy in determining vertical position. A high VDOP value...

A digital nautical chart that represents navigational data using vector graphics, allowing for scalable and interactive mapping of maritime areas. A vector chart is a type of electronic navigational chart (ENC) designed for use in modern marine navigation systems. Unlike raster charts, which are essentially digital images of traditional paper charts, vector charts use mathematical...

The speed at which a vessel is effectively moving towards its intended destination, factoring in both its current speed and the angle of travel relative to the wind or current. Velocity Made Good (VMG) is a crucial concept in sailing and other forms of marine navigation, especially when travelling upwind or downwind. It refers to...