Glossary Archive

Visibility reduced to between 0.5 and 2 nautical miles due to suspension of water particles in the air

Mast aft of the mainmast, on a ship.

Flag semaphore indicating the letter M.

International Morse Code sequence representing the letter M.

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 unique nine-digit number assigned to a vessel, coast station, or group of stations for digital communication and identification in the Global Maritime Distress and Safety System (GMDSS). Maritime Mobile Service Identity (MMSI) is a critical component of modern maritime communication systems, enabling efficient and precise identification of vessels and stations during radio communications. This...

A breakwater made of stone or concrete

A vessel with a single hull

Verb: Mooring Mooring refers to the act of securing a boat or vessel in place using ropes or chains by attaching them to a fixed structure such as a pontoon, dock, buoy, or anchoring. This is typically done to prevent the boat from drifting away due to currents, tides, or winds. Mooring is essential in...