Glossary Archive

A white, forward facing light exhibited near the masthead by a power-driven vessel underway.

Fitting into which the mast heel fits

An internationally recognised distress signal used in voice communication to indicate a grave or imminent, life-threatening emergency at sea. The term "Mayday" is a critical part of maritime communication and one of the pro-words in the Standard Marine Communication Phrases. Originating from the French phrase "m'aider," which means "help me." It is used exclusively in...

The Maritime and Coastguard Agency (MCA) is a UK government agency responsible for implementing maritime safety and environmental policies. It oversees the UK’s search and rescue operations, promotes safety at sea, enforces maritime law, and coordinates responses to pollution incidents. The MCA is part of the Department for Transport. Key Responsibilities of the MCA Search...

The International Maritime Signal Flag Mike. Meaning My vessel is stopped and making no way through the water.

Mean High Water Neaps (MHWN) refers to the average height of the higher of the two daily high tides that occur during neap tides. Neap tides occur when the difference between high and low tide heights is the least, which happens during the first and third quarters of the moon when the sun and moon...

A tidal datum representing the average height of the high water level during spring tides over a specific period, typically measured over a 19-year Metonic cycle. Spring tides occur when the sun, moon, and Earth are aligned, resulting in higher and lower tides. MHWS is an important reference point in maritime navigation, coastal engineering, and...

Mean Low Water Neaps (MLWN) is a tidal datum representing the average lowest water level during neap tides. Neap tides occur when the gravitational pull of the sun and moon are perpendicular to each other, resulting in lower high tides and higher low tides. MLWN is used as a reference point for charting and determining...

Mean Low Water Springs (MLWS) refers to the average sea level during low tide under the gravitational influence of the combined forces of the sun and the moon when they are aligned (i.e., during spring tides). This reference level is used in marine navigation and hydrographic surveying to establish a consistent baseline for charting depths...

A communication made via radio from a vessel to a shore-based medical facility or professional to seek urgent medical advice or assistance for an onboard medical emergency. A Radio Medical Advice Link Call is an essential protocol in maritime operations, particularly for vessels operating far from shore where immediate access to medical facilities is unavailable....