Glossary Archive

The radio frequency range between 3 and 30 megahertz (MHz), commonly used for long-range marine communications via skywave propagation.  High Frequency (HF) radio is an essential communication tool in the maritime industry, particularly for vessels operating beyond the range of Very High Frequency (VHF) and Ultra High Frequency (UHF) systems. HF radio waves can travel...

The UK government agency responsible for producing astronomical and navigational data for maritime and military use.  His Majesty's Nautical Almanac Office (HMNAO) is a division of the UK Hydrographic Office that provides essential astronomical and navigational information for seafarers, the military, and scientific institutions. Established in 1832, it produces publications such as the Nautical Almanac,...

A knot that attaches a rope to an object, such as a post, ring, or other rope. A hitch is a versatile and essential knot where securing a rope to an object is necessary. Unlike a bend, which joins two ropes, or a loop, which creates a fixed or adjustable loop in a rope, a...

This shape represents the Letter H (Flag Semaphore) and the Number 8 (Flag Semaphore).

International Morse Code sequence representing the letter H.

The organisation responsible for search and rescue operations in UK waters. His Majesty's Coastguard (HMCG) is a section of the MCA responsible for initiating and coordinating all maritime search and rescue within the UK Maritime Search and Rescue Region. This includes mobilising, organising and tasking adequate resources and assets, such as the RNLI or coastguard helicopters, to respond to persons in distress...

The UK government agency responsible for producing astronomical and navigational data for maritime and military use.  His Majesty's Nautical Almanac Office (HMNAO) is a division of the UK Hydrographic Office that provides essential astronomical and navigational information for seafarers, the military, and scientific institutions. Established in 1832, it produces publications such as the Nautical Almanac,...

To raise an object vertically, commonly a sail or flag, using a halyard. It typically uses a system of ropes, cables, pulleys, and sometimes a winch or hydraulic mechanism to facilitate lifting.

A sealed onboard container designed to temporarily store wastewater, such as sewage or greywater, until it can be properly discharged at a designated facility. A holding tank is an essential component of a vessel's waste management system, particularly on boats equipped with toilets (marine heads) or sinks. Its primary purpose is to collect and store...

Used in satellite navigation and positioning systems to quantify the accuracy of horizontal position measurements. It is a unitless factor that indicates the geometric quality of the satellite configuration in relation to the receiver's position. A lower HDOP value indicates a more accurate horizontal position, while a higher HDOP value indicates a less accurate position...