Glossary of maritime terminology

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M/E Control System

The M/E control system, or main engine control system, on a ship allows the engine to be remotely controlled. It helps the vessel to change direction and also controls the propeller’s speed rotation directly from the ship’s bridge or engine control room.

Magnetic Compass

A magnetic compass is an instrument that helps a ship’s navigator determine direction and measure the boat's heading (the direction at which the vessel is pointing.) The compass contains a free-floating magnetic element that will align in a north-south direction, pointing towards the earth's magnetic North Pole.

The magnetic North Pole is approximately 1,000 miles from the geographic North Pole however a skilled navigator will be able to determine true North by finding the magnetic North and then correcting for deviation and variation.

Maiden Voyage

A vessel’s first journey it makes after being delivered from the shipyard.

Main Air Compressor

In maritime terminology, the main air compressor on a ship is designed to supply highly pressurized air to start the main and secondary engines. A storage bottle in the compressor stores the pressurized air with the minimum air pressure needed to start the main engine is 30 bars. Main air compressors of varying capacities are available however that capacity must align with the ability to start the main engine. 

Main Clock

The main clock, also called the master clock, controls the secondary or slave clocks that are located throughout a ship. This is so that all of the connected clocks are always displaying the exact same time. The main clock does this by transmitting signals or control pulses to the other clocks in its network. 

Main Deck

The main deck of a ship is the uppermost continuous deck that extends all the way from fore to aft i.e. from bow to stern.

Main Engine

The main engine on a ship refers to any engine that is constructed to supply propulsion power regardless of whether the propulsion system is geared drive, direct-drive, or diesel electric. This engine may be an internal combustion engine or a compression-ignition engine, with the majority of vessels using diesel.

Large ships, such as container ships and cruise ships don’t just have the one engine but will instead operate with two, four or even six engines. This means that the ship’s engine room can be vast in size, even spanning the height of several decks.

Main Engine Control System

The main engine control system, or M/E control system, on a ship allows the engine to be remotely controlled. It helps the vessel to change direction and also controls the propeller’s speed rotation directly from the ship’s bridge or engine control room.

Main Propulsion Boiler

Typically D-type boilers, the main propulsion boilers on a ship are water-tube boilers that provide steam for the vessel’s propulsion turbines. This propel the ship through the water by enabling gear reduction, shafting and propeller movement. 

Main Switchboard

The main switchboard runs all of the electrical power systems on the ship. It receives all of the power that machinery such as the generators and motors produce and redistributes it as electrical energy to other parts of the vessel as needed. The main switchboard is usually located in the main engine room or the machinery control room.

Manifest

In freight terms, the manifest is the Master of the ship’s list of goods and products that make up the vessel’s cargo.

Manning Agency

A manning agency or crewing agency is a company who works with their client, the shipowner, to find seafarers to work onboard their vessels. The manning agent checks that the seafarer has the right certifications and documentation for the position, as well as the correct travel documents. The agent also arranges visas and medical checks for the shipowner.

Marine Aids to Navigation

Marine Aids to Navigation (AtoN) are anything that helps a vessel navigate more safely. They are charted marks and include items such as beacons, lighthouses, buoys, lights, and radio beacons.

Marine Diesel Generator

A marine diesel generator, also known as a diesel generator, or a diesel generator engine serves the purpose of providing electrical power to a vessel’s electrical systems including lighting and the propulsion system whilst at sea.

They are a hybrid of an electric generator and a diesel engine and are specially designed to function in, and withstand, the specific environmental conditions that ships work in, including heavy vibrations, seawater and the salty sea air.

Marine Evacuation System

The marine evacuation system (MES) on a ship falls under the category of life saving appliances and is commonly found on many vessels that carry passengers - such as ferries and cruise ships. The system consists of an inflatable escape chute or slide which enables fast and safe evacuation to the ship’s life rafts waiting in the water below.

Marine Growth Prevention System

In shipping terms, a Marine Growth Prevention System (MGPS) is a means of protecting a ship’s internal salt water systems from corrosion and other damage. It utilizes copper nodes that produce ions which are carried by the sea water into the piping and machinery. The concentration of copper in the solution is less than two parts per billion, however this is adequate to prevent marine life from forming and growing.

Marine Navigation Light

The marine navigation lights on a boat or ship help the navigating officers onboard determine which vessel should give way to another when they encounter each other at night. Navigation lights must be displayed from sunset to sunrise as well as during the day if there is poor or limited visibility, such as in overcast weather or fog. These lights are also referred to as signal lights, or marine signal lights.

Marine Propeller Shaft

The marine propeller shaft, also called just the propeller shaft, is a mechanical component that transfers the power created by the ship’s engines to the propeller or propellers. Essentially it is a shaft that carries a screw propeller at its end. 

Marine Provisions Crane

A freight term, the marine provision crane, also just called a provisions crane, on a ship is, as the name suggests, used to load and unload provisions needed by or for the crew and passengers, such as food and supplies.

Marine Sewage Plant

A marine sewage plant on a ship, also called a sewage treatment plant, is used to treat wastewater on the vessel so that it can either be reused or returned to the ocean. It is crucial that the rules and regulations surrounding the treatment of marine wastewater are followed as any reused water must be safe and returned water must have minimal environmental impact.

Marine Signal Light

The marine signal lights on a boat or ship help the navigating officers onboard determine which vessel should give way to another when they encounter each other at night. Signal lights must be displayed from sunset to sunrise as well as during the day if there is poor or limited visibility, such as in overcast weather or fog. These lights are also referred to as navigation lights, or marine navigation lights.

Marine Surveyor

A shore-based maritime career, a Marine Surveyor is a person who inspects a vessel’s hull or its cargo for damage or quality.

Marine Toilet

A marine toilet, also called a vacuum toilet or ship toilet, is used on boats and ships of all types and sizes. Marine toilets work by removing the waste from the bowl by suction and then depositing it in a holding tank when the toilet is flushed. Traditional toilets, such as those found in the home, use a combination of water and gravity to transport the waste from the bowl to a collection or treatment tank.

Like regular toilets, marine toilets use water to flush although in far smaller quantities - typically around 1.5 liters of water per flush as opposed to the 10 liters used by a non-vacuum toilet.

Marine Wastewater Treatment

Marine wastewater treatment is the act of treating wastewater on a vessel so that it can either be reused or returned to the ocean. It is crucial that the rules and regulations surrounding the treatment of marine wastewater are followed as any reused water must be safe and returned water must have minimal environmental impact.

Maritime

Maritime as an adjective has a couple of meanings. It can mean situated on or near the sea or refer to commerce or navigation by sea. 

Maritime English

Maritime English is the name given to the language seafarers use at sea. It combines English language with specific maritime terms and commands (for example, starboard instead of right or aft, meaning towards the rear of the vessel).

It is used so that seafarers of different native languages can communicate with one another safely and efficiently. A certain level of proficiency in the English language is required by most reputable shipping companies. Maritime English is also known as Seaspeak and Standard Marine Communication Phrases or SMCP.

MARPOL

MARPOL, the International Convention for the Prevention of Pollution from Ships as adopted by the IMO is the main international convention covering prevention of pollution of the marine environment by ships from operational or accidental causes.

Master

In maritime terms, the Master, also referred to as the Captain, is the highest rank of seafarer and the person who is ultimately in charge of, and responsible for, the vessel and her cargo, crew and passengers.

Master Clock

The master clock, also called the main clock, controls the secondary or slave clocks that are located throughout a ship. This is so that all of the connected clocks are always displaying the exact same time. The master clock does this by transmitting signals or control pulses to the other clocks in its network. 

Masthead Light

The masthead light is a white light positioned over the fore and aft centerline of a ship.

Merchant Marines

The Merchant Marines is the term used to describe the United States of America's commercial shipping operations. (It is called the Merchant Navy in most other countries). The vessels in the Merchant Marie's fleet can be anything from cargo and container shipsheavy lift vessels and oil tankers to fishing vessels, ferries and cruise ships.   

Merchant Navy

The Merchant Navy (called the Merchant Marines in the United States) is the term used to describe a country's commercial shipping operations. Vessels in a Merchant Navy's fleet can be anything from cargo and container ships, heavy lift vessels and oil tankers to fishing vessels, ferries and cruise ships

MES

MES stands for marine evacuation system and this falls under the category of life saving appliances. It is commonly found on many vessels that carry passengers - such as ferries and cruise ships. The system consists of an inflatable escape chute or slide which enables fast and safe evacuation to the ship’s life rafts waiting in the water below.

Messman

Depending on the vessel and/or nationality, a Messman might be called a Steward, Steward’s Assistant, General Steward, Galley Utilityman or even Waiter. The Messman is one of the unlicensed Seafarer Ranks and an entry level cargo ship job. The Messman is the go-to person when it comes to anything related to food serving and general hygiene. They help the Cook prep meals, set tables, serve food, prepare tea, coffee and other drinks and ensure water coolers have a fresh supply of water. After meals, they will clear the tables, clean the mess area, and wash the dishes.

MGPS

An MGPS (Marine Growth Prevention System) is a means of protecting a ship’s internal salt water systems from corrosion. It utilizes copper nodes that produce ions which are carried by the sea water into the piping and machinery. The concentration of copper in the solution is less than two parts per billion, however this is adequate to prevent marine life from forming and growing.

Middle Watch

The middle watch, in shipping terms, is the period of being on duty (AKA watch) that takes place onboard a vessel between 0000hrs and 0400hrs.

Mike

Mike stands for the letter M in the International Radiotelephony Spelling Alphabet, which is most often referred to as the NATO Phonetic Alphabet or simply the Phonetic Alphabet. This is the most commonly used group of code words used to clearly communicate the letters of the Roman alphabet, particularly over the radio and is essential in helping seafarers give and receive messages, orders and instructions clearly and correctly.

Minimum Safe Manning

Sometimes also referred to as Manning Scales or Manning Policy, Minimum Safe Manning is the minimum number of seafarers - including officers and crew - that must be onboard a ship for it to be considered safe to sail. The scales are worked out to ensure that there will be sufficient people with sufficient practical ability to meet every possible eventuality at sea.

MKC Online Catalogue

The MKC Online Catalogue is a portal that gives users access to a wealth of information through the IMO's (International Maritime Organization) resources, publications and collections in their Maritime Knowledge Centre (MKC).

MMSI

MMSI stands for Maritime Mobile Service Identity. An MMSI is a nine digit long unique identification number which is sent in digital form over a radio frequency channel in order to ID a vessel. The MMSI relates to the flag country that the ship is sailing under.

Mobile Offshore Drilling Unit

 Often abbreviated to MODU, a Mobile Offshore Drilling Unit is a vessel that engages in drilling operations for the exploration (or exploitation) of resources beneath the sea bed. These could include resources such as liquid or gaseous hydrocarbons. 

Moor

To moor is the act of securing a vessel by anchor or to the shore by ropes, lines or chains.

Mooring Line

A mooring line is a cable, rope or line used to tie up a ship when at a dock.

Mooring Winch

The mooring winch is a type of windlass - a mechanical device with a horizontal axle which is used onboard vessels to multiply the force used by a seafarer, when pulling cables, chains, ropes and hawsers.

Consisting of a drum that is powered either by steam, by electricity or by hand, it rotates around its axis to wind in the cable or chain, wrapping it around it. Mooring winches work on the same principle as capstans, although the latter have a vertical axle as opposed to horizontal.

Morning Watch

The Morning Watch is the period of being on duty (AKA watch) that takes place onboard a vessel between 0400hrs and 0800hrs.

Morse Lamp

The Morse lamp (also called a signal lamp or Aldis lamp) is a hand-held electric lamp which is normally found on the bridge wing of a vessel. It is used to signal Morse code messages via flashing light between ships of all types, including naval and commercial.

Motor Ship

A motor ship is any vessel that is propelled by internal combustion engines. Motor ship is usually abbreviated to MS and used in front of a vessel's name. For example MS Bounty.

Motor Vessel

A motor vessel is any ship that is propelled by internal combustion engines. Motor vessel is usually abbreviated to MV and used in front of a vessel's name. For example MV Bounty.

Motorman

A Motorman is part of a vessel’s engine department. They stand watch with the Engine Officer on duty and will help with repair and maintenance as well as carry out basic tasks in the engine room and around the vessel such as cleaning or painting. They will also have duties that could include making routine checks of machinery, as well as of the bilge and pump rooms, and the tanks. They will inspect equipment such as turbines, condensers, and pumps and will be expected to record their findings and report any issues or problems that they find to their Officers, and safely rectify them if possible.

Multipurpose Ship

A multipurpose ship is any kind of vessel that has the ability to carry different types of cargo which require different methods of handling. These ships include general cargo ships which can carry regular cargo and dry, loose cargo in containers and roro ships which can carry wheeled cargo such as cars and trucks, as well as containers.

Muster Drill

All ships conduct muster drills, also known as lifeboat drills. In maritime terminology, a muster drill is an onboard exercise to ensure that all crew (as well as any passengers) know how to evacuate the vessel in the event of an emergency. International law stipulates that the Master of every ship must make sure that officers, crew and passengers are familiar with the procedure of lowering the lifeboats and evacuating the vessel, and the emergency use of the lifeboats.