Nautical Charter

Nautical Dictionary - Nautical Glossary - Maritime Terminology

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Nautical Dictionary

Nautical Glossary - Maritime Terminology


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A B C D E F G H I J K L M N O P Q R S T U V W X Y Z

Magnetic Bearing
The bearing of an object after magnetic variation has been considered, but without compensation for magnetic deviation.
Magnetic Course
The course of a vessel after magnetic variation has been considered, but without compensation for magnetic deviation.
Magnetic Deviation
Compass error. The difference between the reading of a compass and the actual magnetic course or bearing due to errors in the compass reading. These errors can be caused by metals, magnetic fields and electrical fields near the compass. The act of checking for magnetic deviation is called swinging.
Magnetic North
The direction to which a compass points. Magnetic north differs from true north because the magnetic fields of the planet are not exactly in line with the north and south poles. Observed differences between magnetic and true north is known as magnetic variation.
Magnetic Variation
The difference between magnetic north and true north, measured as an angle. Magnetic variation is different in different geographic locations, so the nearest compass rose to each location on a chart must be used.
Main Beam
Transverse structural member supporting the deck and, in most modern sailboats, the deck-stepped mast; also the designated location of the ship's Official Number and (in some instances) Tonnage (affixed to or cut into the beam)
Main Deck
The uppermost complete deck.
Main Mast
The tallest mast; the forward mast of a yawl or ketch; the mast furthest aft on a schooner
Main Topsail
A topsail on the main mast.
Mainsail
The principal sail that is set on the main mast.
Mainsheet
The line that controls the angle of the mainsail in its relation to the wind.
Make Fast
To attach a line to something so that it will not move.
Make Way
Moving through the water.
Man the Yards
On square-rigged ships, a form of ceremonial salute to honor the visit of a high official. The yards were lined by men standing upon them, and there was also a man standing on the truck of each topgallant mast.
Manhole
A hole in a tank, boiler or compartment on a ship, designed to allow the passage of a man for examination, cleaning, and repairs.
Manifest
A document containing the ship's name and port of registry, a full list of the ship's crew, passengers, full details of her cargo, and other relevant information.
Manila
Before the introduction of man-made fibers, much of the rope used at sea was made from manila. Made from the fibers of banana plants in the Philippines, manila did not rot when it was exposed to seawater.
Marconi Rig
The most common type of sail used today, a triangle-shaped mainsail defined by the mast and one horizontal boom perpendicular to the mast.
Marina
A place where boats can find fuel, water and other services. Marinas also contain slips where boats can stay for a period of time.
Mariner
In general, a person employed in a sea-going vessel. In some cases, applied to a seaman who works on deck.
Marines
Military persons expert at small arms carried aboard warships to kill enemy officers, gunners, etc., also may be used to enforce the captain's authority. 1
Mark
An object used as a reference point while navigating.
Marl
To wrap a small line around another.
Marline
Pronounced "marlin" small line used for whipping, seizing, and lashing.
Marling Hitch
Used for lashing down sails, awnings, etc., a series of round turns where the end is passed over the standing part and under the bight and pulled taut on each turn.
Marlinspike
Pointed tool used for line work, for opening line strands for splicing, and especially for prying tight knots apart.
Marlinspike Sailor
One who is adept at splicing, knotting, and working with line and canvas.
Maroon
To deliberately put a sailor ashore and leave him there while the ship sails away.
Marry, to
The operation of bringing two lines together; term also applied to other objects.
Marry the Gunner's Daughter
Old Navy nickname for a flogging, particularly when across a gun.
Martingale
On square-rigged ships, the stay which holds the jib-boom down against the pull of the fore topgallant-mast stays.
Mast
The vertical pole or spar that supports the boom and sails. a mast on a mechanically propelled vessel holds electronics antennas, lights, etc.
Mast Boot
A protective cover wrapped around the mast at the deck on a keel stepped boat to prevent water from entering the boat.
Mast Head
The top of the mast
Mast Hoops
Rings around a mast which can slide vertically, attached to the forward edge of a sail, which hold the sail in place. 1
Mast Partners
Reinforcements for a mast where it passes through a deck. 1
Mast Slot/Groove
The opening up the back (aft) edge of the mast in which the mainsail luff rope slides when it is hoisted. Some masts have an external sail track.
Mast Step
The fitting in the bottom of the boat in which the bottom or heel if the mast sits.
Mast Tangs
Fittings on the mast to which the forestay and shrouds attach.
Mast Track
A track or groove in the back of the mast to which the sail is attached by means of lugs or the bolt rope.
Master
The Captain of a vessel. Highest officer aboard ship. Oversees all ship operations. Keeps ships records. Handles accounting and bookkeeping. Takes command of vessel in inclement weather and in crowded or narrow waters. Handles communications.
Master-At-Arms
The person empowered by the captain to be armed if necessary to maintain order or make arrests. 1
Masthead
The top of a mast.
Masthead Light
Also known as a steaming light. The masthead light is a white light that is visible for an arc extending across the forward 225° of the boat. When lit the masthead light indicates that a vessel under power, including sailboats with engines running. Masthead lights are usually located halfway up the mast rather than at the top.
Masthead Rig
A design in which the forestay runs to the top of the mast.
Mate
A deck officer ranking next below that of master. Usually divided into first, second, third, etc. to indicate seniority.
MAYDAY
An internationally recognized distress signal used on a radio to indicate a life threatening situation. Mayday calls have priority over any other radio transmission and should only be used if there is an immediate threat to life or vessel. Mayday comes from the French M'aidez which means help me. For urgent situations that are not immediately life threatening there is the PAN PAN identifier. Less urgent messages such as navigational hazards should send a SECURITE message.
Mean Low Water (MLW)
A figure representing the average low tide of a region.
Mean Lower Low Water (MLLW)
There are two low tides in each tidal cycle (so usually two low tides in each day). These two low tides are not quite the same height because one tide is generated by the gravitational interaction with the sun (which is small), and the other is generated by the gravitational interaction with the moon (which is not so small). Since the two low tides (or water levels) are different levels of low, one is naturally the higher low water (higher low tide) and the other is the lower low water (lower low tide). So Mean Lower Low Water is the average of the lower low water height of each tidal day (ie average of the lowest low tide from each day). The averages are taken over a period called the National Tidal Datum Epoch (a 19-year epoch).
Measured Mile
A course marked by buoys or ranges measuring one nautical mile. Measured miles are used to calibrate logs.
Mediterranean Berth
A method of docking with a boat's stern to the dock.
Meet Her
An order to the helmsman to put on opposite rudder to check the swing of the ship.
1 Mercator Projection
Method of producing a chart in which the parallels of latitude and the meridians of longitude intersect each other at right angles.
Merchant Navy
The merchant ships on the official registers of any nation.
Meridian
A semi great circle joining the north and south poles. Known as lines of longitude, they cross the equator and all parallels of latitude at right angles.
Mermaid
A mythical creature, half human and half fish.
Mess
Dining room facilities and kitchen for crew separate from the passenger dining room and kitchen.
Mess Deck
Where meals are eaten
Messenger
A small line used to pull a heavier line or cable. The messenger line is usually easier to throw, lead through holes or otherwise manipulate than the line that it will be used to pull.
Messroom
A dining room on a ship.
Meteorology
The study of weather patterns in order to predict changes in the weather.
Midchannel Buoy
A red and white vertically striped buoy used in the United States to mark the middle of a channel. Midchannel buoys may be passed by on either side.
Middle Ground
Shoal area between two navigational channels.
Midshipman
A non-commissioned naval rank. Midshipmen play a part, under supervision, in most of the ship's activities, and are in training for higher command.
Midships
In the middle portion of the boat Roughly halfway between a ship's stem and stern, and where the beam usually is the widest.
Midwatch
the watch or work shift beginning at midnight, usually lasting until 4:00am or 8:00am.
1 Mile
Distance at sea is measured in nautical miles, which are about 6067.12 feet, 1.15 statute miles or exactly 1852 meters. Nautical miles have the unique property that a minute of latitude is equal to one nautical mile Measurement of speed is done in knots where one knot equals one nautical mile per hour.
Millibar
A unit used to measure the barometric pressure of the atmosphere. 1 millibar equals 0.03 inches of mercury.
Mizzen
A small sail set on the mizzenmast.
Mizzenmast
The mast aft of the mainmast in a sailing ship the shorter mast behind the main mast on a ketch or yawl, or the third aftermost mast of a three-masted schooner or square-rigged ship.
Mold
A pattern or template. Also a shape of metal or wood over or in which an object may be hammered or pressed to fit.
Mold Loft
The large enclosed floor where the lines of a vessel are laid out and the molds or templates made.
Monkey
(1) A small wooden cask in which grog was carried. (2) A type of marine steam reciprocating engine where two engines were used together on the same propeller shaft.
Monkey Fist
A large heavy knot usually made in the end of a heaving line to aid in accurate throwing.
Monkey Jacket
A thick serge jacket worn by seamen while keeping watch at night or in stormy weather.
Monohull
A boat with one hull.
Mooncusser
Legendary opportunists who lured vessels onto shoals during nights when there was no moonlight to illuminate the coastline.
Moonraker
On square-rigged ships, a small light square sail set above the skysail in fair weather. If the sail were triangular, it would be called a Skyscraper.
Moor
To attach a boat to a mooring, dock, post, anchor, etc.
Mooring
An anchor or weight, permanently attached to the sea floor, with a buoy going to the surface, used to hold the boat in a certain area.
Mooring Bitt
A strong pair of iron, steel or wooden posts on a ship's deck, around which ropes or cables are wound and held fast.
Mooring Buoy
A buoy secured to a permanent anchor sunk deeply into the bottom.
Mooring Line
A line used to secure a boat to an anchor, dock, or mooring.
Morse Code
A language of "dots" and "dashes" used to send messages, either sound using radio waves, or light using a searchlight or Aldis lamp.
Motor
(1) An engine. (2) The act of using an engine to move a boat.
Motor-sailing
Sailing with the motor on and in gear
Mount
An attachment point for another object.
Mouse
Any small collar made with spunyarn or light line to hold something in place.
Mouse a Hook
The passing of several turns of line across the jaw of a hook to prevent something on the hook, such as an eye or a line, from jumping clear.
Mudhook
Sailor's slang for anchor.
Multi-Hull
A vessel formed of two or more hulls. A catamaran has two hulls, and a trimaran has three hulls.
Mushroom Anchor
A type of anchor with a heavy inverted mushroom shaped head. Mushroom anchors are used to anchor in mud and other soft ground.
Muster
To assemble passengers and/or crew.
Mutiny
A forceful resistance to recognized authority. A refusal to obey a legal order of a superior officer is also considered mutiny.

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