Glossary — M

47 terms starting with M.

• Magnetic Bearing
  A bearing measured clockwise from magnetic north, requiring correction for variation to obtain a true bearing.
• Magnetic Compass
  A compass that aligns with Earth's magnetic field to indicate magnetic north; required as backup on all SOLAS vessels.
• Main Engine (ME)
  The primary propulsion engine driving the ship's propeller shaft, typically a large slow-speed two-stroke diesel on cargo ships.
• Mandatory Pilotage
  A legal requirement in certain ports or waterways that a licensed pilot must be employed to navigate a vessel through that area.
• Marine Diesel Oil (MDO)
  A distillate fuel oil with low sulfur content, used in auxiliary engines and during port operations where ECA rules apply.
• Marine Pollutant (MP)
  Substance identified in IMDG Code as harmful to the marine environment; carries the 'Marine Pollutant' (dead-fish-and-tree) mark.
• Marine Superintendent
  A senior shore-side manager responsible for the nautical operations, safety, and compliance of vessels in a company fleet.
• Maritime Labour Convention 2006 (MLC)
  ILO convention establishing minimum working, living, and social security standards for seafarers worldwide.
• Maritime Rescue Coordination Centre (MRCC)
  National coordinating centre that receives distress alerts and orchestrates SAR operations within a defined Search and Rescue Region (SRR).
• Maritime Security Centre — Horn of Africa (MSCHOA)
  EU NAVFOR coordination centre supporting BMP transits and convoy escort tasking.
• MARPOL (International Convention for the Prevention of Pollution from Ships) (MARPOL)
  The IMO's principal environmental convention — six annexes covering oil (I), noxious liquid substances (II), harmful packaged substances (III), sewage (IV), garbage (V), air pollution + GHG (VI).
• MARPOL Annex I
  The annex of MARPOL regulating prevention of pollution by oil, covering operational discharges and accidental spills from ships.
• MARPOL Annex II
  The annex of MARPOL controlling discharge of noxious liquid substances carried in bulk, applicable to chemical tankers.
• MARPOL Annex III
  Regulations for the prevention of pollution by harmful substances carried at sea in packaged form.
• MARPOL Annex V
  The annex of MARPOL governing disposal of garbage from ships, prohibiting most plastics discharge into the sea.
• MARPOL Annex VI
  The annex of MARPOL setting limits on sulphur oxides, nitrogen oxides, and other air pollutant emissions from ships.
• MARPOL Bunker Sample
  Representative sample drawn at the bunker manifold during delivery, sealed and retained for 12 months.
• Mast Riser
  A large-diameter high-velocity vent pipe fitted to a tanker's mast to discharge cargo vapours safely above ignition sources.
• Master
  The certificated officer in overall command of a vessel, legally responsible for the safety of the ship, crew, cargo, and environment.
• Material Safety Data Sheet (MSDS)
  A document providing information on the hazards, handling precautions, and emergency procedures for a chemical or dangerous cargo.
• Medical First Aid Guide (MFAG)
  IMO/WHO/ILO guide for treating injuries arising from incidents with dangerous goods aboard ship.
• Mercator Sailing
  A method of solving rhumb line problems using the properties of a Mercator chart to find course and distance between positions.
• Metacentric Height (GM)
  The vertical distance between the centre of gravity (G) and the metacentre (M), the primary indicator of a vessel's initial stability.
• Metacentric height (GM) (GM)
  The distance between the centre of gravity (G) and the metacentre (M) — the primary indicator of transverse initial stability.
• Metacentric Height from Keel (KM)
  Vertical distance from keel to the metacentre M; sum of KB (keel to centre of buoyancy) and BM (metacentric radius).
• METAREA
  One of twenty-one geographic areas for which meteorological services co-ordinate the broadcast of marine weather forecasts.
• Methanol as Marine Fuel
  Liquid alcohol fuel adopted by some newbuild container and tanker fleets; bunkered at ambient temperature, simpler infrastructure than LNG.
• MF/HF SSB
  Single-side-band radio in MF (1.6–4 MHz) and HF (4–27 MHz) bands used for medium- and long-range maritime voice and DSC.
• Minimum Safe Manning
  Flag-state-issued document specifying the minimum manning by rank/qualification for safe operation of the ship.
• MLC 2006 (Maritime Labour Convention) (MLC)
  The ILO Maritime Labour Convention 2006 — the seafarers' bill of rights covering employment, hours + rest, accommodation, food + catering, medical care, and repatriation.
• MLC Financial Security
  The MLC 2006 A2.5.2 + A4.2.1 mandatory insurance covering seafarer repatriation + wages during abandonment + shipowner liability for occupational injury/death.
• MLC Financial Security — Abandonment
  MLC 2014 amendment requiring shipowners to maintain insurance/financial security for repatriation, wages, and essential needs of abandoned seafarers.
• MMSI (Maritime Mobile Service Identity)
  Nine-digit numerical address used to identify ships, coast stations, and devices in DSC, AIS, and satellite distress alerting.
• MMSI Number (MMSI)
  A nine-digit Maritime Mobile Service Identity used to identify a ship's radio and AIS transmissions uniquely.
• MOB AIS (Man Overboard AIS)
  Personal AIS beacon worn by crew that activates on water immersion, broadcasting AIS position reports with an MMSI beginning 972 to identify a man-overboard casualty.
• Moment to Change Trim 1 cm (MCT1cm)
  The trimming moment in tonne-metres needed to alter a vessel's trim by one centimetre, used in stability calculations.
• Monsoon
  A seasonal reversal of prevailing winds affecting the Indian Ocean and western Pacific, bringing heavy rainfall on its wet phase.
• Moonpool
  Vertical opening through the hull of an offshore vessel allowing equipment to be lowered from a sheltered indoor location.
• Mooring
  Securing a vessel to a berth, buoy, or anchor using lines, chains, or anchors to keep it stationary.
• Mooring Equipment Guidelines 4 (MEG4)
  OCIMF guideline (2018) for mooring system design, operation, and inspection of tankers and gas carriers.
• MoorMaster
  Cavotec vacuum mooring system replacing conventional lines in some ferry, container, and bulk berths.
• Motorman
  An engine room rating who assists engineers with machinery operation, maintenance, and watchkeeping duties.
• MSI (Maritime Safety Information)
  Umbrella term for navigational warnings, meteorological forecasts, distress relays, SAR information, and piracy reports broadcast to ships under the GMDSS framework.
• MSL (Maximum Securing Load) (MSL)
  The maximum load a cargo-securing device may sustain — used in cargo-securing calculations per the CSS Code.
• Multipurpose Support Vessel (MPSV)
  OSV combining DP, large deck, crane, ROV, and accommodation for varied subsea/inspection/maintenance work.
• multipurpose vessel (MPP)
  Versatile geared cargo ship carrying containers, breakbulk, project cargo, and heavy lifts in a single voyage, typically 3 000–15 000 DWT.
• Muster Station
  A designated assembly point where crew and passengers gather when an emergency alarm is sounded prior to abandoning ship.