AFT - Toward the rear of the ship.

AMIDSHIPS - The middle of the ship, either lengthwise or widthwise, or both.

ARMILLARY SPHERE - A skeleton model of the celestial sphere generally with the earth in the center. An outer ring shows the equator, poles, tropics, zodiacs, etc. Inner rings depict the sun, moon, and stars.

ASTROLABE - (From the Greek "astrer" [star] and "labin" [to take].) An astronomical instrument used by ancient Greeks and others to measure the height above the horizon of celestial bodies. The Seaman's astrolabe was a simple device used for measuring the altitude of the sun or a star for fixing one's approximate latitude. It consists of a heavy brass ring fitted with an alidade or sighting rule pivoted at the center of the ring. Suspended vertically from a shackle at the top of the ring, the alidade was positioned to sight the sun or star and the angle was read off on-scale marks on the ring.

BACK-STAFF - A navigational instrument introduced in the sixteenth century for measuring the altitude of the sun. It gained its name because the user had the sun behind him when taking an observation. Also known as a Davis Quadrant.

BALLAST - Any heavy material such as lead, concrete, or stones placed low in a vessel to increase stability.

BAROMETER - An instrument, often using a column of mercury, for measuring atmospheric pressure. Traditionally a falling barometer measurement meant an approaching storm.

BEARING DIAL - A navigational device used to determine the position of the sun and moon when the Pole Star was not visible, especially during the constant daylight of summer. It was reputed to have been used by the Vikings.

BILGE - The lowest part of a vessel's hull:, where any water in the hull collects.

BIREME - Greek or Phoenician fighting ship that could be powered by sail or oar. Devised about 700 B.C., it had two decks

BOW - The front of a vessel.

CARAVEL - A small three-masted vessel developed in the fourteenth century. This adaptable ship could be rigged with lateen- or square-rigged sails. The Nina was one of these.

CARTOGRAPHER - Person who makes maps. Cartography is the science and practice of projecting by various methods an area of the Earth's surface on a flat plane, as a sheet of paper.

CARVEL - The planks are laid close together on their edges, attached to the ribs to form a smooth exterior.

CHART - A map displaying various graphic representations. Often these are maps of waterways. Early versions of these water charts were called portolans.

CHIP LOG AND REEL - A device for measuring the speed of a vessel through the water. It consisted of a triangular piece of wood, weighted on one side and attached to a line with marked (knots) lengths. When thrown from the stern of a vessel the line was allowed to run out for a specified time. The number of knots that had come off the reel determined the vessel's speed. This traditional way of measuring is no longer used, but a ship's speed is still referred to in knots.

CHRONOMETER - A mechanical device for keeping time independent of ship's motion. See Captain Cook.

CLINKER - The edges of the planks are overlapped to form an irregular exterior, much like siding on a house. Also called lapstrake.

COG - A twelfth-century Northern European trading vessel that was clinker-built and square-rigged.

COMPASS - An instrument whose magnetized metal needle aligns itself with the magnetic fields of the earth. This causes one end of the needle to point north. Mariners used this information to navigate the ship. The Chinese are said to have invented the first compass over 2000 years ago. See lodestone.

COMPASS ROSE - A circle divided into 32 points for a total of 360 degrees and printed on a chart as a means of determining the course of a vessel.

CROSS-STAFF - An early sixteenth-century instrument for measuring the altitude of a heavenly body. It consists of a square shaft and a sliding cross-piece set at right angles to the shaft. The shaft end is held at the observer's eye and the cross-piece positioned to line up with the sun and the horizon. The cross-piece marks a point on the shaft that is referred to in a table of degrees and minutes.

DEAD RECKONING - Deductive reckoning. Estimating location and speed using a variety of different methods including wind, waves, bird sightings, and current.

DECK - Floors on a ship. Each level is called a deck.

DHOW - A long, flat sailing vessel that is lateen-rigged and found in the Indian Ocean along the east coast of Africa, the Arabian peninsula, Pakistan, and India.

DRAFT - The depth of water required to float a vessel.

FORE - The front part of a ship.

FOREMAST - The forwardmost mast on a vessel with three or more masts.

GUNWALE - The top rail of the side of a boat or ship.

HAND LEAD AND LINE - A means of finding the depth of water near the coasts. It consists of a rope, with length markings, attached to a lead weight of about seven pounds. The lower end of the weight is cupped and filled with tallow. The depth of the water is equal to the length of line played out. The tallow picks up material from the bottom from which, after some experience, the location of the vessel can be determined.

HOG TRUSS - A rope stretched taunt from bow to stern to give the ship longitudinal strength. The hog truss was used only on early ships built without a keel.

HULL - The outer body or shell of a vessel, floating partially immersed in water and supporting the remainder of the vessel.

KEEL - The backbone of a ship. The lowest and principle timber of a wooden ship and to which the stempost, sternpost, and ribs are attached.

LAPSTRAKE - See clinker.

LATEEN RIGGED - A triangular sail set at an angle to a short mast. Northern Europeans who went to the Mediterranean named them after the word "latin."

LATITUDE - Imaginary lines running east to west on the surface of the earth. The latitude determines location north or south on the globe.

LODESTONE - (From the old English, "lad" [leader or guide], thus the guiding stone for mariners.) It is a magnetized piece of iron ore that can impart its north-south properties to an iron needle. This needle was then used to make a compass.

LONGITUDE - Imaginary lines that run north to south on the surface of the earth. The prime meridian is 0 degrees. Each 15 degrees of longitude equals one hour of time.

MAINMAST - On ships with two or more masts, it is the secondmast.

MAST - A vertical pole usually made of wood or metal that supports the sails.

MASTHEAD - The top of a lower mast to which a topmast is attached.

MERIDIAN - A great circle passing through the poles and denotedin degrees of longitude east and west of Greenwich, England.

MIZZENMAST - The third mast on ships with three or more masts.

NAO - Fourteenth-century square-rigged ship with two to four masts. In later times they achieved great size. Also called a carrack.

NORTH STAR - A second magnitude star found at the end of the handle of the Little Dipper and almost at the north celestial pole. Also called the Pole Star or Polaris.

PILOT - A person who navigates a vessel. Historically another name for "navigator," usually different from the master or captain. Today a pilot navigates the ship in specific bodies of water.

PLANKS - The timbers forming the outermost covering of the hull.

POOP - A partial deck above the main deck located aft.

PORT - The left side of a vessel. This side of the ship traditionally pulled up to the dock.

QUADRANT - A simple instrument for determining the altitude of heavenly bodies It is a quarter of a circle with a plumb bob suspended from its apex. Held vertically and aligned with the sun or a star, the plumb line (string with a weight on it) falls across the scale of degree markings from 0-90 degrees on the curved edge, indicating the angle of elevation.

RIB - The frames or timbers of a ship that rise from the keel to form the shape of the hull.

RUDDER- A device mounted near the stern of a vessel to control direction.

SAIL - An assemblage of cloth cut to various sizes and shapes (i.e., square and triangular), and designed to catch the wind and use its force to propel a vessel.

SAND GLASS - A device for measuring the passage of time aboard ship before developmentof the chronometer. It consists of two vacuum globes connected by a narrow neck. Sand runs from the top globe into the bottom one through the neck, emptying itself in a predetermined period of time. The sand inside was often made of ground eggshells or ground marble. Usually supplied to a ship in four sizes: half-minute, half-hour, one hour and four hour glasses. Also called an ampolletta.

SCURVY - A deficiency of vitamin C. Symptoms include nausea, weakness, loss of hair and teeth, and eventual death. It was caused by a lack of fruits and vegetables in the diet. More sailors died of this than any other cause.

SQUARE RIGGED - Square or rectangular sails on two or more masts.

STARBOARD - The right side of a vessel. The term is derived from "steering board" a large, paddle- shaped board used to steer ancient boats. Traditionally this board was on the right side of the ship.

STERN - The back of a vessel.

SUNDIAL - A device that when properly aligned projects the shadow of the sun on a scaled surface, thus indicating the time of day.

TRAVERSE BOARD - An old and approximate means for recording the course of a ship during a watch four-hour period of time. It consisted of a piece of wood marked out with a compass rose and eight holes bored along each point. Every half-hour (by sand-glass time) a peg was inserted into a hole marking the compass point on which the ship had run. At the end of the watch, the mean course during the watch was determined from the position of the eight pegs.

YACHT - Name given to any boat used for pleasure cruises or racing.