Glossary
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TermDefinition
- General Nautical Terminology, Safety Look-out
A crew member assigned to maintain a continuous watch for potential hazards, other vessels, or navigational markers while at sea.
A look-out...
More Details - General Nautical Terminology, Navigation LOP
Navigational lines drawn on a chart, each representing a possible location of a vessel based on a single observation or measurement.
A line...
More Details - General Nautical Terminology Lose WayA vessel loses way when she slows down and stops in the water
- General Nautical Terminology, Navigation Lowest Astronomical Tide (LAT)
The lowest level that sea tides can reach under normal meteorological conditions, based on astronomical influences such as the gravitational pull...
More Details - General Nautical Terminology Lubber LineThe marker in the compass which is aligned with the fore-and-aft line of the boat against which the course can be read off on the compass card
- General Nautical Terminology Luff
The leading edge, which is the part of the sail that faces the wind when the sail is set correctly.
The luff of a sail is a critical part of...
More Details - General Nautical Terminology Luff Up
To steer a sailing vessel closer to the wind, reducing the angle between the boat's heading and the direction of the wind.
"Luff up" is a...
More Details - General Nautical Terminology LullA temporary drop in wind speed
- General Nautical Terminology, Weather (Meteorology) Lundy
Sea area of the Met Office Shipping Forecast. Lies in the Bristol Channel, around Lundy Island off southwest England.
Named for Lundy Island...
More Details - General Nautical Terminology Magnetic North
Magnetic North refers to the direction indicated by a magnetic compass, which points towards the Earth’s magnetic north pole. This differs from...
More Details - Organisation MAIB
A UK government agency responsible for investigating marine accidents and incidents to improve maritime safety. Part of the Department for...
More Details - General Nautical Terminology Mail SailTo hoist the sails and get under way
- General Nautical Terminology Mainsail
The principal and typically largest sail on a sailing vessel, attached to the mainmast and used to harness wind power for propulsion.
The...
More Details - General Nautical Terminology Mainsheet Traveller
The mainsheet traveller is a system on a sailboat that allows for adjustment of the mainsheet attachment point along a track that runs across the...
More Details - General Nautical Terminology Make FastTo secure the vessel with mooring lines to the jetty or to tie up to a buoy
- General Nautical Terminology Making Way
A vessel that is moving through the water under its own power, whether by engine, sail, or other means.
A vessel is said to be "making way"...
More Details - General Nautical Terminology, Weather (Meteorology) Malin
Sea area of the Met Office Shipping Forecast. Located off the north coast of Ireland, near Malin Head.
After Malin Head, Ireland’s northernmost...
More Details - General Nautical Terminology, Safety Man Overboard
A situation where a person has fallen from a vessel into the water, requiring immediate rescue actions.
A man overboard situation is one of...
More Details - General Nautical Terminology Marina
A specially designed harbour or dock where boats and yachts are moored, often offering services such as refuelling, repairs, and...
More Details - Organisation Marine Accident and Investigation Branch (MAIB)
A UK government agency responsible for investigating marine accidents and incidents to improve maritime safety. Part of the Department for...
More Details - Courses, RYA Marine Radio VHF (SRC)The RYA Marine Radio VHF (SRC) course is a mandatory qualification for anyone operating a marine VHF radio with Digital Selective Calling (DSC).... More Details
- Organisation Maritime and Coastguard Agency (MCA)
The Maritime and Coastguard Agency (MCA) is a UK government agency responsible for implementing maritime safety and environmental policies. It...
More Details - General Nautical Terminology, Safety Maritime Mobile Service Identity (MMSI)
A unique nine-digit number assigned to a vessel, coast station, or group of stations for digital communication and identification in the Global...
More Details - General Nautical Terminology Maritime Rescue Coordination Centre (MRCC)
A shore-based facility responsible for coordinating and managing maritime search and rescue (SAR) operations within a designated area of...
More Details - General Nautical Terminology, Navigation Maritime Safety Information
Defined in the Safety of Life at Sea (SOLAS) Convention, Chapter IV as "navigational and meteorological warnings, meteorological forecasts and...
More Details - General Nautical Terminology MARPOL
Established by the IMO, MARPOL is the convention for preventing pollution from ships. It is the main international convention covering the...
More Details - General Nautical Terminology Mast
A tall vertical spar or structure on a sailing vessel that supports the sails, rigging, and sometimes navigation equipment.
A mast is one of...
More Details - General Nautical Terminology Masthead light
A white, forward facing light exhibited near the masthead by a power-driven vessel underway.
- General Nautical Terminology Mast StepFitting into which the mast heel fits
- General Nautical Terminology, Safety, Signals & Communication MayDay
An internationally recognised distress signal used in voice communication to indicate a grave or imminent, life-threatening emergency at...
More Details - Organisation MCA
The Maritime and Coastguard Agency (MCA) is a UK government agency responsible for implementing maritime safety and environmental policies. It...
More Details - Flag / Pennant, Signals & Communication Code Flag Mike (M)

The International Maritime Signal Flag Mike.
Meaning
My vessel is stopped and making no way through the water.
- General Nautical Terminology Mean High Water Neaps (MHWN)
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...
More Details - General Nautical Terminology, Navigation Mean High Water Springs (MHWS)
A tidal datum representing the average height of the high water level during spring tides over a specific period, typically measured over a...
More Details - General Nautical Terminology Mean Low Water Neaps (MLWN)
Mean Low Water Neaps (MLWN) is a tidal datum representing the average lowest water level during neap tides. Neap tides occur when the...
More Details - General Nautical Terminology, Safety MEDILINK
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...
More Details - General Nautical Terminology, Signals & Communication Medium Frequency (MF)
The range of radio frequencies between 300 kHz and 3 MHz, commonly used in marine communication and navigation systems.
Medium Frequency (MF)...
More Details - General Nautical Terminology, Organisation, Weather (Meteorology) Met Office
The United Kingdom's national meteorological service, responsible for providing weather and climate-related services, including marine...
More Details - General Nautical Terminology, Signals & Communication MF
The range of radio frequencies between 300 kHz and 3 MHz, commonly used in marine communication and navigation systems.
Medium Frequency (MF)...
More Details - General Nautical Terminology MHWN
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...
More Details - General Nautical Terminology, Navigation MHWS
A tidal datum representing the average height of the high water level during spring tides over a specific period, typically measured over a...
More Details - Phonetic Alphabet, Signals & Communication Mike
Pronounced: MIKE
The term for the letter M in the NATO Phonetic Alphabet.
- General Nautical Terminology MistVisibility reduced to between 0.5 and 2 nautical miles due to suspension of water particles in the air
- General Nautical Terminology, Weather (Meteorology) Mistral
A strong, cold, and dry northwesterly katabatic wind that blows from southern France into the Mediterranean, particularly affecting the Gulf of...
More Details - General Nautical Terminology Mizzen MastMast aft of the mainmast, on a ship.
- Flag Semaphore, Signals & Communication Letter M (Flag Semaphore)

Flag semaphore indicating the letter M.
- Morse Code, Signals & Communication Letter M (Morse Code)
International Morse Code sequence representing the letter M.
- General Nautical Terminology MLWN
Mean Low Water Neaps (MLWN) is a tidal datum representing the average lowest water level during neap tides. Neap tides occur when the...
More Details - General Nautical Terminology, Safety MMSI
A unique nine-digit number assigned to a vessel, coast station, or group of stations for digital communication and identification in the Global...
More Details - General Nautical Terminology Mole
A solid structure, often made of stone or concrete, built to protect a harbour, anchorage, or shoreline from the effects of waves and currents,...
More Details - General Nautical Terminology MonohullA vessel with a single hull
- General Nautical Terminology Mooring
A permanent structure or equipment, such as a buoy, anchor, or dock, used to secure a vessel in place or the act of securing a vessel to a fixed...
More Details - General Nautical Terminology Mooring Buoy
A non-navigational floating device anchored to the seabed, used for securing vessels in place without the need for traditional anchoring.
A...
More Details - General Nautical Terminology Mooring RingA ring on a mooring buoy
- General Nautical Terminology Motor sailing
A sailing vessel making way using sails and engine. A downward pointing cone should be displayed in the fore triangle in daylight and lights for...
More Details - General Nautical Terminology MRCC
A shore-based facility responsible for coordinating and managing maritime search and rescue (SAR) operations within a designated area of...
More Details - Courses, RYA Multihull Club RacingThe RYA Multihull Club Racing course prepares sailors to participate in local club races with confidence. The course covers race rules, starting... More Details
- Courses, RYA Multihull Day SailingThe RYA Multihull Day Sailing course prepares sailors to undertake safe and enjoyable day trips on multihulls. Participants learn about trip... More Details
- Courses, RYA Multihull Level 1 - Start SailingThe RYA Multihull Level 1 course introduces participants to the basics of sailing multihulls. Participants practice rigging, steering, and sail... More Details
- Courses, RYA Multihull Level 2 - Basic SkillsThe RYA Multihull Level 2 course builds on the skills learned in Level 1, focusing on independent sailing in multihulls. Participants practice... More Details
- Courses, RYA Multihull Level 3 - Better SailingThe RYA Multihull Level 3 course refines sailors’ techniques, focusing on advanced boat handling and performance optimization. Participants... More Details
- Courses, RYA Multihull Performance SailingThe RYA Multihull Performance Sailing course is designed for experienced sailors looking to optimize their skills in high-performance multihulls.... More Details
- Courses, RYA Multihull Regional RacingThe RYA Multihull Regional Racing course is tailored for sailors competing at a regional level in multihull events. This advanced program focuses... More Details
- Courses, RYA Multihull Sailing With SpinnakersThe RYA Multihull Sailing With Spinnakers course focuses on spinnaker handling in multihulls. Participants learn to rig, hoist, and trim... More Details
- Courses, RYA Multihull Seamanship SkillsThe RYA Multihull Seamanship Skills course builds essential practical skills for handling multihulls in a variety of conditions. Participants... More Details
- Courses, RYA Multihull Start RacingThe RYA Multihull Start Racing course introduces sailors to the fundamentals of racing multihulls. Participants practice starting techniques, boat... More Details
- General Nautical Terminology National Oceanic and Atmospheric Administration (NOAA)
The National Oceanic and Atmospheric Administration is an American scientific agency within the United States Department of Commerce that focuses...
More Details - Organisation NATO
An intergovernmental military alliance established in 1949 aimed to ensure the collective defence of its member state through political and...
More Details - General Nautical Terminology Nautical Almanac
A comprehensive publication containing astronomical data and navigational information essential for maritime navigation.
A Nautical Almanac is...
More Details - General Nautical Terminology, Navigation Nautical Mile
A nautical mile is a unit of measurement used in maritime navigation that is equivalent to one minute of latitude or approximately 1.852...
More Details - General Nautical Terminology, Navigation Navigational Telex (NAVTEX)
A maritime communication system used for the automatic broadcast of navigational and meteorological warnings, forecasts, and urgent safety...
More Details - General Nautical Terminology Navigation Lights
A system of coloured and white lights displayed on a vessel to indicate its position, heading, and status to other vessels, especially during low...
More Details - General Nautical Terminology, Navigation NAVTEX
A maritime communication system used for the automatic broadcast of navigational and meteorological warnings, forecasts, and urgent safety...
More Details - Flag / Pennant, Signals & Communication Code Flag November (N)

The International Maritime Signal Flag November.
Meaning
Negative.
- General Nautical Terminology NDB
A radio transmitter at a fixed location that emits signals in all directions, used in marine navigation to help vessels determine their position...
More Details - General Nautical Terminology Neap RangeThe difference in height between HW and LW on a Mean (average) neap tide.
- General Nautical Terminology, Navigation Neap Tide
When the difference between high and low water is at its smallest, typically occurring twice a month during the first and third quarters of the...
More Details - Weather (Meteorology) Near Gale
Sometimes used to describe wind strength approaching a Gale.
- Organisation NLB
The Northern Lighthouse Board is a maritime organisation responsible for maintaining lighthouses and navigation aids in Scotland and the Isle of...
More Details - Flag Semaphore, Signals & Communication Letter N (Flag Semaphore)

Flag semaphore indicating the letter N.
- Morse Code, Signals & Communication Letter N (Morse Code)
International Morse Code sequence representing the letter N.
- General Nautical Terminology, Navigation NM
A Notice to Mariners is an official publication issued by maritime authorities to provide important information and updates regarding...
More Details - General Nautical Terminology NOAA
The National Oceanic and Atmospheric Administration is an American scientific agency within the United States Department of Commerce that focuses...
More Details - General Nautical Terminology Non-Directional Beacon (NDB)
A radio transmitter at a fixed location that emits signals in all directions, used in marine navigation to help vessels determine their position...
More Details - Organisation North Atlantic Treaty Organization (NATO)
An intergovernmental military alliance established in 1949 aimed to ensure the collective defence of its member state through political and...
More Details - Organisation Northern Lighthouse Board (NLB)
The Northern Lighthouse Board is a maritime organisation responsible for maintaining lighthouses and navigation aids in Scotland and the Isle of...
More Details - General Nautical Terminology, Weather (Meteorology) North Utsire
Sea area of the Met Office Shipping Forecast. Located in the northern North Sea, adjacent to Utsira Island off the west coast of Norway.
Derived...
More Details - General Nautical Terminology, Navigation Notice to Mariners (NM)
A Notice to Mariners is an official publication issued by maritime authorities to provide important information and updates regarding...
More Details - Abbreviation, General Nautical Terminology Not Under Command (NUC)
A ship that, due to exceptional circumstances, is unable to manoeuvre as required by the International Regulations for Preventing Collisions at...
More Details - Phonetic Alphabet, Signals & Communication November
Pronounced: no-VEM-ber
The term for the letter N in the NATO Phonetic Alphabet.
- Abbreviation, General Nautical Terminology NUC
A ship that, due to exceptional circumstances, is unable to manoeuvre as required by the International Regulations for Preventing Collisions at...
More Details - Flag / Pennant, Signals & Communication Numeral 4 (Flag Pennant)

The flag represents the numerical value of four.
- Flag / Pennant, Signals & Communication Numeral 5 (Flag Pennant)

The flag represents the numerical value of five.
- Flag / Pennant, Signals & Communication Numeral 6 (Flag Pennant)

The flag represents the numerical value of six.
- Flag / Pennant, Signals & Communication Numeral 7 (Flag Pennant)

The flag represents the numerical value of seven.
- Flag / Pennant, Signals & Communication Numeral 8 (Flag Pennant)

The flag represents the numerical value of eight.
- Flag / Pennant, Signals & Communication Numeral 9 (Flag Pennant)

The flag represents the numerical value of nine.
- Flag / Pennant, General Nautical Terminology, Signals & Communication Numeral Pennant
A triangular flag used in maritime signalling to represent numerical digits, typically in conjunction with other signal flags.
A numeral...
More Details - Flag Semaphore, Signals & Communication Numerals-Numbers Follow (Flag Semaphore)

This flag semaphore signal indicates a change from letters to numbers (Numbers Follow), indicating that the signaller will be using the...
More Details - Abbreviation, Light Characteristic Oc
A light with more light than dark (is on for longer than it is off).
Occulting refers to a type of navigational light in which the light is...
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