Aback. The condition of a sailing ship when the pressure of the wind on the sails has a tendency to drive it astern.

Abaft. Towards the stern; aft, relative to.

Abandon. To leave, to forsake. Usually descriptive of the act of leaving a ship when it is no longer safe or seaworthy.

Abeam. At right angles to the vessel’s longitudinal axis and in her plane of flotation.

Aboard. On or in a ship.

About. A ship is said to come about when in beating to windward it changes its course allowing the wind to bear on the opposite side of the sails. To change from the starboard to the port tack or the reverse.

Aboveboard. Above deck as distinguished from in the hold or below decks.

Abreast. Over against; opposite. See also Abeam.

Access Hole. A hole cut through a portion of a vessel’s structure in order to permit ingress to or egress from a given space or compartment.

Accommodation Ladder. See Ladder, Accommodation.

Accumulator, Hydraulic. A tank designed to store water under pressure.

Accumulator, Pneumatic. A tank designed to store air under pressure.

Acetylene. A gas produced by the action of water upon calcium chloride. This gas combined with oxygen burns with a very hot flame.

Acid Open Hearth Steel. See Steel and Iron.

Acidity, Boiler. A term used when the feed water in a boiler is acid.

Admiralty Coefficient. See Coefficient, Admiralty.

Admiralty Drafts. Specifications, establishments, plans, outlines drawn up, given by the Admiralty to naval and civil dockyards for the construction of a vessel and/or its appurtenances. These even included the figureheads and "gingerbread" work in the days of sail, especially during the seventeen years between 1773 to 1790 when, to reduce costs, an Admiralty order required that drawings should be officially approved for all carved works on new ships.

Admiralty Metal. Described under Metals.

Admiralty Pump. See Pump, Admiralty.

Adrift. Afloat without effective means of propulsion or control.

Adze. A carpenter’s tool having its blade set at right angles with a long curved handle and used for trimming

ship timbers. The act of trimming the timbers with this tool is called "dubbing."

Aft. In the direction of or toward the stern.

After Collision Bulkhead. See Bulkhead, After Peak.

After Deck. See Deck, After.

After Peak. A compartment immediately forward of the sternpost. Generally situated entirely below the load waterline.

After Peak Bulkhead. See Bulkhead, After Peak.

After Perpendicular. A line perpendicular to the base line, intersecting the after edge of the stern post at the designed waterline.

Aground. The situation of a ship in which its bottom touches or rests on the ground; stranded.

Ahead. Forward; in front of.

Air Casing, Stack. A ring-shaped plate coaming surrounding the stack and fitted at the upper deck, just below the umbrella. Its purpose is to protect the deck structure from heat and to help ventilate the fire room.

Air Compressor. An auxiliary designed to furnish air under pressure for pneumatic tools, cleaning purposes etc. A form of compressor in common use is the single stage type.

Air Courses. A wood ship term applied to air spaces running fore and aft in the sides or bottom of a vessel to provide for a circulation of air to prevent decay in the timbers.

Air Ejector. A steam ejector connected to the condenser dry suction for the purpose of discharging the air and vapor into the atmosphere. A condensate pump handles the condensed steam.

Air Hammer. An air-driven tool arranged to deliver rapid longitudinal impulses against one end of a steel pin. It is contained in a cylindrical shaped casing about three inches in diameter and two feet long with a pistol grip at the opposite end from the pin. Various shaped tools can he fitted on the outer end of the pin to perform such operations as heading up rivets or caulking and chipping.

Air Holding on Hammer. A tool to hold against the head of a rivet while it is being driven. Its head is fitted on a piston which is cushioned in a cylinder filled with compressed air.

Air Pipes. Pipes leading from tanks to the open air as vents or to provide a supply or escape of air when pumping out or filling the tanks.

Air Port. See Port, Air.

Air Propellers or Beeswing Fans. A fan usually consisting of from two to four blades operated by an electric motor, the blades being so shaped that the air leaves the fan at right angles to its plane of rotation.

Air Pump. See Pump, Air.

Air Pump, Dry Vacuum. See Pump, Air, Dry Vacuum.

Air Pump, Dual. See Pump, Air, Dual.

Air Resistance. See Resistance, Air.

Air Tight Door. See Door, Air Tight.

Air Trunk or Conduit. The passage forming the main air supply to a fan or exhaust from a fan.

Air Valve. See Valve, Air.

Air and Circulating Pump. See Pump, Air and Circulating.

Alarm Valve. See Valve, Alarm.

A-lee. Away from the wind. A sailing ship which constantly requires the helm to be moved to the side of the vessel away from the direction from which the wind is coming in order to keep his course is said to carry a-lee helm.

Alkalinity, Boiler. A term used when the feed water in a boiler is alkaline and has the power of neutralizing acids.

All Hands. Every person on board a ship.

Alligator Shear. See Sheer, Alligator.

Aloft. In the tops or upper rigging; on the yards; above the decks.

Alongside. Parallel and in close proximity to. Used frequently relative to a ship lying parallel and close to another ship or a pier.

Allow. Low in or on; below.

Alternating Current. An electric current in which the instantaneous values of current at any point in the circuit vary from zero to a positive maximum value, back to zero; then to a negative maximum value and back to zero. When plotted it consists of half waves of equal area in successive opposite direction from the zero line.

Aluminum Paint. See Paint.

Amidships. In the vicinity of the middle portion of a vessel as distinguished from her ends. The term is used to convey the idea of general locality but not that of definite extent.

Ammeter. An instrument for measuring the electric current flowing in a circuit. The scale of the meter is calibrated to read in amperes.

Ammonia. A volatile alkali, a transparent, pungent gas that can be easily liquefied by pressure. It is used extensively as a refrigerating medium for cold storage systems aboard ship.

Ammonia Joint. On account of the penetrating nature of ammonia, great care should be taken with the joints in a refrigerating system where alkali is used. The joints should be made of wrought iron or steel, the connections should be soldered after they are screwed in place. Lead gaskets should be placed between flanges and lead or white metal packing used for the valve stems.

Ampere. The practical unit of electric current. It represents that value of current which will cause the electrolytic deposition of silver at the rate of 0.001118 gm. per second.

Analysis of Flue Gas. See Boiler, Analysis of Flue Gas.

Anchor. A heavy iron or cast steel implement attached to a vessel by a rope or chain cable. When the anchor is thrown overboard it lays hold of the ground and holds the vessel in its place. The earlier anchors were made of wood, with one arm and later with two. Stones were attached to give weight to sink and to increase holding power. An iron anchor, having a wood stock, followed the wood anchor. This in turn was replaced by an all-metal anchor. The solid or old-fashioned anchor consisted of the shank, the ring (shackle or Jew’s harp), the arms, and the stock. The shank is the main body of the anchor, having the ring bolted to one end and the arms welded to the other, the crown being the heavy end of the shank from which the arms branch out, The stock is the beam attached to the shank opposite the arms. Various patent anchors exist, most of which are stockless and have their arms pivoted upon the shank and the palms in the plane of the arms.

Anchors, Bowers. The principal anchors carried by a vessel. They are so named because they are carried on the bows. In earlier times they were of different weights, the larger being known as the best bower and the smaller as the small bower. These anchors are now usually the same size.

Anchor Deck. See Deck, Anchor.

Anchor Handling Gear. The windlass and gear installed aboard ship, for letting go, taking in and handling the anchor.

Anchor, Kedge. A term applied to a light anchor used for warping or kedging.

Anchor, Mooring. A term applied to a second or extra anchor used for holding a ship at her mooring.

Anchor, Sea. A device constructed of spars and canvas in the form of a parachute, to which is bent a hawser or cable. It is put overboard in a heavy sea for the purpose of keeping a vessel head-on to the sea and to enable her to ride out the gale. Also termed a driving anchor or drag.

Anchor, Stream. An anchor used for anchoring in a narrow roadway or channel to prevent the stern swinging with the tide. The weight of this anchor is equal to about one-fourth that of the bower anchor.

Anchorage. A suitable place for a ship to lie at anchor. Harbor dues for anchoring in a port.

Anemometer. A gauge for measuring the speed and direction of the wind, with rotating vanes and recording dial graduating from 1 to 12 Beaufort scale, or in meters per second. Invented in 1727, early rotary examples were hand held and used with a 15 or 30-second Sand Glass. Later examples were fixed to the mast.

Aneroid Barograph or Barometer. An instrument to measure and record on paper the variations of atmospheric pressure during a period of time. First of the two main types is Vidi’s barograph or barometer that consists of several metal vacuum chambers, with an interior spring to prevent their being damaged by crushing. They were compressed by atmospheric pressure changes, these being noted by a stylus on a drum. The sensitivity of the instrument depended on the number of vacuum chambers in it. The second type is the Bourdon aneroid barometer, which contains a vacuum tube, elliptical in section and bent to form a circle. Changes in pressure alter the tube’s section and increase or reduce the circle’s diameter, this being mechanically noted on a drum by a stylus or a dial by a needle.

Angle. An abbreviation for angle iron or angle bar.

Angle Bar. A rolled shape, generally of mild steel, having a cross section shaped like the legs of a right angle. In ship work it is used for frames, bulkhead stiffeners, attachment of one plate or shape to another, etc. The size is denoted by dimensions of cross section and weight per running foot.

Angle Bar Frame. See Frame, Angle Bar.

Angle Bars, Frame. See Frame, Angle Bars.

Angle Clip. A term applied to a short piece of angle bar used for attachment.

Angle Iron. See Angle Bar.

Angle Valve. See Valve, Angle.

Angle Furnace. See Furnace, Bar.

Angle smiths. Workmen who forge steel shapes such as angle or channel bar into the various parts of the ship’s hull and fittings such as watertight staples and collars, door frames, etc.

Anneal. To soften metal by heating and slowly cooling. In annealing cast iron the carbon is burned out, near the surface, leaving the outer surface tough and strong while the interior is hard.

Annunciator. An electrical device for giving an audible and visible signal.

Annunciator Wire. See Electric Wire and Cable.

Anti-Corrosive Paint. See Paint.

Anti-Fouling Paint. See Paint.

Anvil. An iron or steel block used as a table on which metals are worked or forged. Where an iron block is used the working face is generally made of steel. It is usual to provide a hole about 1¹/₄in. square for holding working tools such as hardies, fuller blocks, etc. Anvils are used in a shipyard by blacksmiths, angle smiths and flange turners.

Apeak. In a vertical direction or nearly so. The anchor is "apeak" when the cable has been hauled

into a nearly vertical line and the vessel is then "hove apeak." A yard when raised by one end, until

nearly vertical is "apeak."

Aperture. The space provided between the propeller and stern post for the propeller.

Appendages. Such items as shafting, struts, bossing, docking and bilge keels, propellers, rudder and any other feature, extraneous to the hull and generally immersed.

Apprentice. A learner or student of a trade.

Apron. A reinforcing timber bolted to the after side of the stem.

Apron Plate. See Plate, Apron.

Arc, Electric. The luminous vapor of great brilliancy and high temperature between the tips of two electrodes.

Arc, Lamp. See Lamp, Arc.

Arch Piece of Stern Frame. The curved portion of the frame over the screw aperture, joining the propeller and stern posts.

Arching. Occasionally used as descriptive of the same phenomenon as the term "hogging."

Architect, Naval. See Naval Architect.

Ardency. That property of a ship by virtue of which she tends to throw her head up into the wind. Ships having this characteristic must be held on their course by keeping the helm a-weather. The reason for this tendency is found in the resultant lateral resistance of the vessel being before or ahead of her resultant wind pressure.

Area of Sections. The area of any cross section of the immersed part of a vessel, the cross section being taken at right angles to the centerline of the vessel.

Armature. The armature of a generator or motor is that part of the machine containing the winding in which the electromotive force is generated. For direct-current machines, it is usually revolving, while for alternating-current machinery it is usually stationary. The two essential parts of all generators and motors are the field magnet, which produces the necessary magnetic flux, and the armature on which the conductors are arranged.

Armillary Sphere. An item of navigational equipment, made of wood and brass. The name is derived from the Latin armilla, meaning a hoop or bracelet. Such spheres were first made by the ancient Greeks, having sights and being used for astronomical observations. They were widely used on ships in the 16th and 17th centuries to discover the solar system’s important coordinates. The earth is shown as a small globe in the center of the sphere, which is itself formed by two rings at right angles to the line of the poles. Another broad ring, representing the equator, joins them at their midpoint. The globe representing the earth is, in some large examples, made of wood or glass, and shows the oceans and continents. The tropics of Cancer and Capricorn, and the arctic and antarctic circles, are represented by four narrower rings. A broad ring crossing the narrow tropic rings at an angle represents the ecliptic or path of the sun. The sphere is mounted in a meridian ring that is set itself in an equatorial ring. The polar axis angle of the armillary sphere could be adjusted to set the latitude. The sphere would be rotated on this axis to take the time factor into account. Portable armillary spheres for use at sea were generally contained in a two-halved, rounded case that supported the horizontal ring, and they were small and compact. The armillary sphere was superseded in the early 18th century by the Orrery.

Artificial Horizon. An instrument to take hydrographic sightings at a mooring during calm weather, or on land. It was also used during conditions of poor visibility, fog and heavy rain, when the true horizon was obscured. A pioneer attempt at such an instrument was John Elton’s attachment of two spirit levels to a Hadley’s Octant. This was not very successful, but two types of artificial horizon were developed later. One was the enclosed level mercury horizon of 1812. It had a separate trough and spare bottle of mercury to refill the horizon. The second was the mirror horizon, which had adjustable legs and was provided with a separate spirit level to check that the instrument was standing correctly. Both types were housed in a wooden box with hinged lid when not in use.

Asbestos. Principally a silicate of magnesia combined with water. It is used in varying forms where resistance to combustion is necessary. A fireproof composition used for insulation, packing, and lagging.

Ash Chute. A portable iron trough by means of which ashes are discharged overboard clear of the vessel’s side.

Ash Ejector. An apparatus for utilizing the discharge water from a pump to convey ashes from the fire room up and out through the vessel’s side above the waterline. It consists of a metal pipe or chute leading overboard above the waterline. At the lower end in the fire room a hopper is located, and into this the discharge from the pump is led. With the hopper closed and discharge valve opened the stream from the pump will pass with high velocity. The cover may then he removed and ashes dumped into the hopper from which they will be rapidly conveyed overboard by the water.

Ash Expeller. An apparatus for the discharge of ashes from the fire room below the water level. This type is of value in the case of war vessels when it is desirable to make an opening through the side armor. In this apparatus the ashes are placed in the hopper, from which they pass through a quick acting valve to an intermediate chamber. An air blast or hydraulic jet expels them from this chamber.

Ash Hoist. Gear for the removal of ashes from the fire room. It consists of a bucket, usually traveling in guides, a winch for hoisting same to weather deck, and sometimes a trolley track to ship’s side.

Ash Pit, Boiler. See Boiler Ash Pit.

Ashore. Aground (when said of a ship); on shore or land as opposed to aboard of afloat.

Asphalt Solution. See Paint.

Assemble. To collect and place in the proper positions, the various members or fabricated parts entering into construction.

Astern. Signifying position, in the rear of or abaft the stern; as regards motion, the opposite of going ahead; backwards.

Astracal. A small molding placed on the front of one of a pair of doors near the inside edge to cover the joint where the two doors come together when closed.

Asynchronous Generator. See Generator, Asynchronous.

Athwart, Athwartship. In a transverse direction; from side to side at right angles to the fore and aft centerline of a vessel.

Astrolabe. An instrument dating back to ancient Greek, Persian and Arab times for ascertaining the positions of the heavenly bodies. It was primitively a kind of sextant, made obsolete by the eventual introduction of the quadrant and sextant.

Atlantic Neptune Prints. These prints were commissioned about 1780 by the British Admiralty for use during the American War of Independence, and showed American ports, harbors, landscapes and charts.

Augmenter, Vacuum. An apparatus consisting of a steam ejector and a small condenser with suitable connections and designed to diminish the condenser pressure and enhance the vacuum. A steam jet is installed in an air suction pipe leading from the top of the main air pump suction or from an independent connection to the condenser. The air and vapor entrained are delivered to a small condenser in which the pressure is higher. Circulating water for the augmenter condenser is taken from a by-pass on the circulating pump discharge to the condenser, or from a connection to the front head of the main condenser. The ejector steam and the vapor drawn from the main condenser are densified in the augmentor and a water seal is interposed between the augmentor suction and the air pump to prevent the air and vapor from escaping back to the main condenser.

Augsburg Dial. A type of Sun dial specifically one of the Diptych dial types, made Of gilt and silvered brass and of ivory, comprising an hour-graduated ring, the plane of this being angled to coincide with the observer’s latitude. A perpendicular axial gnomon at the ring’s center is aligned to represent the polar axis. There is a hexagonal base plate. During use the ring of the instrument shows the shadow of the sun moving at a regular speed around it. Emanating from Augsburg in Germany at first.

Auxiliary Circulating Pump. See Pump, Auxiliary Circulating.

Auxiliary Feed Pump. See Pump, Auxiliary Feed.

Auxiliary Foundations. See Foundation, Auxiliary.

Auxiliary Machinery. As its name implies, it includes all machinery except the boilers and engines constituting the propelling machinery proper, and the deck machinery. Under this heading are included such items as Air Pumps, Ash Ejectors, Blowers, Bilge Pumps, Circulating Pumps, Condensers, Distillers, Evaporators, Fans, Feed Heaters, Feed Pumps, Filters, Injectors, Lubricating Oil Pumps, Oil Pumps, Sanitary Pumps, Transfer Pumps, Water Pumps, etc.

Avast. A command to cease pulling on a rope. Stop, cease.

Avast-heaving. A term used on shipboard as a command to stop pulling in the anchor chain.

Awning. A canvas canopy spread over a vessel’s decks, bridges, etc., for protection against rain and sun.

Awning Deck. See Deck, Awning.

Awning Deck Sheer strake. The strake of outside plating adjacent to the awning deck.

Awning Deck Stringer. See Stringer, Awning Deck.

Awning Deck Stringer Bar. See Stringer, Bar.

Axis, Neutral. See Neutral Axis.

Azimuth Circle. A graded ring attached to a compass. it is used in taking the bearings of the sun, stars and terrestrial objects.

Azimuth Compass and Vertical Compass. A form of compass divided into degrees, with vertical sights used for taking the azimuth of a star. The azimuth of a star is the distance of that body in angular degrees from north or south point of the meridian: the angular distance measured along the horizon between the meridian of a place and the vertical circle passing through the center of a celestial object and the zenith. Designed with an azimuth circle, and made in England by Ralph Walker, 1793, the instrument was part of the standard equipment, as a bearing compass, of Royal Navy ships between 1795 and 1819. With it, magnetic variation could be measured to about a tenth of a degree, and it supposedly solved problems of longitude, but the achievements of this very sensitive compass were never fully appreciated or utilized because of the lack of knowledge of the laws of magnetic deviation at that time.