ABDC: Abbreviation for after bottom dead centre.

ABSOLUTE PRESSURE: Gauge pressure plus atmospheric pressure.

ABSOLUTE TEMPERATURE: The temperature measured when absolute zero is used as a reference. Absolute zero is - 273.16°C or .469.69°F, and is the lowest measured temperature known.

ABT: Abbreviation for automatic bus transfer; an automatic electric device that supplies power to vital equipment. This device will shift from the normal power supply to an alternate power supply any time the normal supply is interrupted.

ACCELERATION: The rate of increase of velocity per time unit (for example, seconds, minutes, or hours).

ACCESSORY DRIVE: A drive consisting of gears, chains, or belts of secondary importance, not essential in itself but essential for the operation of engine accessories (fuel pump, water pump, and so forth).

ACCUMULATOR: A device used for storing liquid under pressure; sometimes used to smooth out pressure surges in a hydraulic system.

ACTUATOR: A device that uses fluid power to produce mechanical force and motion.

ADDITIVE: A material that is added to improve fuel or oil.

ADVANCE: To set the timing of the injection pump or injectors for an earlier injection.

AFTERCOOLER: A device used on turbo-charged engines to cool air that has undergone compression.

AIR BIND: The presence of air in a pump or pipes, which prevents the delivery of liquid.

AIR BLEEDER: A device that removes air from a hydraulic system. Types include a needle valve, capillary tubing to the reservoir, and a bleed plug l

AIR CLEANER: A device (filter) for removing unwanted solid impurities from the air before the air enters the intake manifold.

AIR COMPRESSOR: A device used to increase air pressure.

AIR EJECTOR: A jet pump that removes air and noncondensable gases.

AIR-FUEL RATIO: The ratio (by weight or by volume) between air and fuel.

AIR GAP: The distance between two components.

AIR-STARTING VALVE: A valve that admits compressed air to the air starter for starting purposes.

ALIGN: To bring two or more components of a unit into the correct positions with respect to one another.

ALLOY: A mixture of two or more different metals, usually to produce improved characteristics.

ALLOWANCE: The difference between the minimum and the maximum dimensions of proper functioning.

ALTERNATING CURRENT (a.c.): Current that is constantly changing in value and direction at regularly recurring intervals.

AMBIENT TEMPERATURE: The temperature of the surrounding environment.

AMMETER: An instrument for measuring the rate of flow of electrical current in amperes.

AMPERE: The basic unit of electrical current.

ANNEAL: To heat a metal and to cool it in such a manner as to toughen and soften it. Brass or copper is annealed by heating it to a cherry red colour and dipping it suddenly into water while hot. Iron or steel is slowly cooled from the heated condition to anneal.

ANNUNCIATOR: A device, usually electro-mechanical, used to indicate or transmit information. See ENGINE ORDER TELEGRAPH.

ANTIFRICTION BEARING: A bearing containing rollers or balls plus an inner and outer race. The bearing is designed to roll, thus minimizing friction.

API: Abbreviation for American Petroleum Institute.

API GRAVITY: Gravity expressed in units of standard API (hydrometer).

ARC: Portion of a curved line or of the circumference of a circle.

ARCING: Electrons leaping the gap between the negative and the positive poles.

ARMATURE: The movable part of a relay, regulator, or horn, or the rotating part of a generator or starter.

ATDC: Abbreviation for after top dead centre.

ATMOSPHERE: The mass or blanket of gases surrounding the earth.

ATMOSPHERIC PRESSURE (BAROMETRIC PRESSURE): The pressure exerted by the atmosphere, averaging 14.7 psi at sea level with a decrease of approximately 1/2 pound per 1000 feet of altitude gained.

ATOMIZATION: The spraying of a liquid through a nozzle so the liquid is broken into tiny droplets or particles.

AUTOMATIC CONTROLLER: An instrument or device that operates automatically to regulate a controlled variable in response to a set point and/or input signal.

AUTOMATIC CONTROL SYSTEM: A system of instruments or devices arranged systematically to control a process or operation at a set point without assistance from operating personnel.

AUTOMATIC OPERATION: Operation of a control system and the process under control without assistance from the operator.

AUXILIARY MACHINERY: Any system or unit of machinery that supports the main propulsion units or helps support the ship and the crew. Examples of auxiliary machinery are pumps, evaporators, steering engines, air-conditioning and refrigeration equipment, laundry and galley equipment, deck winches, and so forth.

AXIAL: In a direction parallel to the axis. Axial movement is movement parallel to the axis.

AXIS: The centreline running lengthwise.

BABBIT: An antifriction metal lining for bearings that reduces the friction between moving components.

BACKLASH: The distance (play) between two movable components.

BACK PRESSURE: A pressure exerted contrary to the pressure producing the main flow.

BAFFLE: A device which slows down or diverts the flow of gases, liquids, sound, and so forth.

BALANCED VALVE: A valve in which the fluid pressure is equal on both sides (the opening and closing directions).

BALL BEARING: A bearing that uses steel balls as its rolling element between the inner and outer ring (race).

BALL CHECK VALVE: A valve consisting of a ball held against a ground seat by a spring. It serves to check the flow or to limit the pressure of a liquid or substance.

BAROMETER: An instrument which measures atmospheric pressure.

BBDC: Abbreviation for before bottom dead centre.

BDC: Abbreviation for bottom dead centre. The position of a reciprocating piston at its lowest point of travel.

BEARING: A mechanical component which supports and guides the location of another rotating or sliding member.

BEARING CLEARANCE: The distance between the shaft and the bearing surface.

BELL BOOK: An official record of engine orders received and answered.

BIMETALLIC: Composed of two metals with different rates of expansion, which curve to a greater, or lesser, extent when subjected to temperature changes.

BLEEDER: A small cock, valve, or plug that drains off small quantities of air or fluids from a container or system.

BLOCK DIAGRAM: A diagram in which the major components of a piece of equipment or a system are represented by squares, rectangles, or other geometric figures, and the normal order of progression of a signal or current flow is represented by lines.

BLOWBY: Exhaust gases that escape past the piston rings.

BLOWER: A low-pressure air pump, usually a rotary or centrifugal type of pump that supplies air above atmospheric pressure to the combustion chambers of an internal - combustion engine.

BLUEPRINTS: Copies of mechanical or other types of technical drawings.

BOILER: Any vessel, container, or receptacle that is capable of generating steam by the internal or external application of heat. The two general classes are fire tube and water tube.

BOILER BLOW PIPING: Piping from the individual boiler blow valves to the overboard connection at the skin of the ship.

BOILER DESIGN PRESSURE: Pressure specified by the manufacturer, usually about 103% of normal steam drum operating pressure.

BOILER FEEDWATER: Deaerated water in the piping system between the deaerating feed tank and the boiler.

BOILER LOAD: The steam output demanded from a boiler, generally expressed in pounds per hour (lb/hr).

BOILER REFRACTORIES: Materials used in the boiler furnace to protect the boiler from the heat of combustion.

BOILER WATER: The water actually contained in the boiler.

BONNET: A cover used to guide and enclose the tail end of a valve spindle.

BORE: A cylinder hole or the inside diameter of a cylinder or hole.

BOSCH METERING SYSTEM: A metering system with a helical groove in the plunger which covers or uncovers ports in the pump barrel.

BOTTOM BLOW: A procedure that removes suspended solids and sludge from a boiler.


BOURDON TUBE: A C-shaped hollow metal tube that is used in a gauge for measuring pressures of 15 psi and above. One end of the C is welded or silver-brazed to a stationary base. Pressure on the hollow section forces the tube to try to straighten. The free end moves a needle on the gauge face.

BOYLE’S LAW: The volume of any dry gas varies inversely with the applied pressure, provided the temperature remains constant.

BRAKE HORSEPOWER (bhp): The usable power delivered by an engine.

BRAKE MEAN EFFECTIVE PRESSURE (bmep): Mean effective pressure acting on the piston, which would result in a given brake horsepower output if there were no losses from friction, cooling, or exhaust. Bmep is equal to mean indicated pressure times mechanical efficiency.

BRAKE THERMAL EFFICIENCY: Ratio of power output (in the form of brake horsepower) to equivalent power input (in the form of heat from fuel.

BRAZING: A method of joining two metals at high temperature with a molten alloy.

BREAKER POINTS: Metal contacts that open and close a circuit at timed intervals.

BRINE: (1) A highly concentrated solution of salt in water, normally associated with the over-board discharge of distilling plants. (2) Any water in which the concentration of chemical salts is higher than seawater.

BRITISH THERMAL UNIT (Btu): A unit of heat used to measure the efficiency of combustion. It is equal to the quantity of heat required to raise 1 pound of water 1°F.

BRUSH: The conducting material, usually a block of carbon, bearing against the commutator or slip rings through which the current flows in or out.

BTDC: Abbreviation for before top dead centre.

BULL GEAR: The largest gear in a reduction gear train-the main gear, as in a geared turbine drive.

BUS BAR: A primary power distribution point connected to the main power source.

BUSHING: A renewable lining for a hole in which a shaft, rod, or similar part moves.

BUS TRANSFER: A device for selecting either of two available sources of electrical power. It may be accomplished either manually or automatically.

BUTTERFLY VALVE: A lightweight, relatively quick acting, positive shutoff valve.

BYPASS: To divert the flow of gas or liquid. Also, the line that diverts the flow.

CALIBRATE: To make adjustments to a meter or other instrument so that it will indicate correctly with respect to its inputs.

CAM: A rotating component of irregular shape. It is used to change direction of the motion of another part moving against it. (For example, rotary motion is changed into reciprocating or variable motion.)

CAM FOLLOWER (VALVE LIFTER): A part that is held in contact with the cam and to which the cam motion is imparted and transmitted to the push rod.

CAM NOSE: That portion of the cam that holds the valve wide open. It is the high point of the cam.

CAMSHAFT: A shaft with cam lobes.

CAMSHAFT GEAR: The gear that is fastened to the camshaft.

CAPACITOR: An arrangement of insulated conductors and dielectrics for the accumulation of an electric charge with small voltage output.

CARBURETOR: An apparatus for supplying atomized and vaporized fuel mixed with air to an internal-combustion engine.

CARRYOVER: (1) Boiler water entrained with the steam (by foaming or priming). (2) Particles of seawater trapped in vapour in a distilling plant and carried into the condensate.

CASING: A housing that encloses the rotating element (rotor) of a pump or turbine.

CASING THROAT: An opening in a turbine or pump casing through which the shaft protrudes.

CASUALTY: An event or series of events in progress during which equipment damage and/or personnel injury has already occurred. The nature and speed of these events are such that proper and correct procedural steps are taken to limit damage and/or personnel injury only.

CASUALTY POWER SYSTEM: Portable cables that are rigged to transmit power to vital equipment in an emergency.

CATALYST: A substance used to speed up or slow down a chemical reaction, but is itself unchanged at the end of the reaction.

CELSIUS: The temperature scale with a freezing point of 0° and a boiling point of 100°, with 100 equal divisions (degrees) between. This scale was formerly known as the centigrade scale.

CENTRIFUGAL FORCE: A force exerted on a rotating object in a direction outward from the centre of rotation.

CETANE VALUE: A measure of the ease with which diesel fuel will ignite.

CHECK VALVE: A valve which permits fluid flow in one direction, but prevents flow in the reverse direction.

CHEMICAL ENERGY: Energy stored in chemicals (fuel) and released during combustion of the chemicals.

CHLORIDE: A compound of the chemical element chlorine with another element or radical.

CIRCUIT: An arrangement of interconnected electrical components that offers a route for current between the two points of the power source.

CIRCUIT BREAKER: An electromagnetic or thermal device that opens a circuit when the current in the circuit exceeds a predetermined amount. Circuit breakers can be reset.

CIRCULATING WATER: Water circulating through a heat exchanger (condenser or cooler) to transfer heat away from an operating component.

CLARIFIER: A water tank containing baffles that slow the rate of water flow sufficiently to allow heavy particles to settle to the bottom and light particles to rise to the surface. This separation permits easy removal, thus leaving the “clarified” water. The clarifier is sometimes referred to as a settling tank or sedimentation basin.

CLOSED COOLING SYSTEM: Consisting of two entirely separate circuits-a freshwater circuit and a seawater circuit.

CLUTCH: A form of coupling that connects or disconnects a driving or driven member.

COMMUTATOR: The copper segments on the armature of a motor or generator. It is cylindrical in shape and is used to pass power into or from the brushes.

COMPRESSION STROKE: That stroke of the operating cycle during which air is compressed into a smaller space creating heat by molecular action.

COCK: A valve that is opened or closed by a quarter turn of a disk or a tapered plug. When a plug is used, it is slotted to correspond with the ports in the valve.

COLD IRON CONDITION: An idle plant, when all services are received from an external source such as shore or tender.

COMBUSTION: The burning of fuel in a chemical process accompanied by the evolution of light and heat.

COMBUSTION AIR: The air delivered to a boiler furnace, engine, or gas turbine combustor to support burning of atomized fuel.

COMBUSTION CHAMBER: The chamber in which combustion mainly occurs.

COMBUSTION-CHAMBER VOLUME: The volume of the combustion chamber (when the piston is at TDC) measured in cubic centimetres.

COMBUSTION CYCLE: A series of thermo-dynamic processes through which the working gas passes to produce one power stroke. The full cycle is-intake, compression, power, and exhaust.

COMPENSATING DEVICE: Mechanical or hydraulic action which prevents overcorrection of change.

COMPONENT: Individual unit, or part, of a system; also, the major units which, when suitably connected, comprise a system.

COMPRESSION RING: The piston rings used to reduce combustion leakage to a minimum.

CONDENSATE: In a distilling plant, the product resulting from the condensation of steam (vapour) produced by the evaporation of seawater. Condensate may also be referred to by different names such as freshwater, freshwater distillate, or distillate.

CONDENSATE DEPRESSION: The difference between the temperatures of condensate in the condenser hot well and the saturation temperature corresponding to the vacuum maintained in the condenser.

CONDENSATION: The change from a gaseous (or vapour) state to a liquid state.

CONDENSER: A heat transfer device in which vapour is condensed to liquid.

CONDUCTANCE: The ability of a material to conduct or carry electrical or thermal energy. Electrical conductance is the reciprocal of the resistance of the material and is expressed in mhos.

CONDUCTION: Heat transfer by actual contact between substances or from molecule to molecule within a substance.

CONDUCTIVITY: The ease with which a substance transmits electricity.

CONDUCTOR: Any material suitable for carrying electric current.

CONSOLE: A panel equipped with remote manual controls and visual indicators of system performance.

CONTROL AIR SUPPLY: Clean, dry air at proper pressure for operation of pneumatic control equipment.

CONTROLLER (electrical): A device used to stop, start, and protect motors from overloads while they are running.

COOLER: Any device that removes heat. Some devices, such as oil coolers, remove heat to waste in overboard seawater discharge; other devices, such as ejector coolers, conserve heat by heating condensate for boiler feed-water.

COOLING SYSTEM: Heat removal process that uses mechanical means to remove heat to maintain the desired air temperature. The process may also result in dehumidification.

CORROSION: A gradual wearing away or alteration of metal by a chemical or electro-chemical process. Essentially, it is an oxidizing process, such as the rusting of iron by the atmosphere.

COTTER, PIN, SPRING: A round split pin used to position and secure a nut on a bolt. The pin is passed through a hole in the nut and bolt. The ends of the pin opposite its head are forced apart by a screwdriver, pliers, or similar tool, thus preventing the cotter from slipping out.

COUNTERBALANCE: A weight, usually attached to a moving component that balances another weight.

COUNTERBORE: (1) The enlargement of the end of a hole for receiving and recessing the head of a screw or bolt below or flush with the surface. (2) A tapered enlargement at the end of an engine cylinder to reduce ridging by the piston’s top compression ring.

COUNTERSUNK HOLE: A hole tapered or bevelled around its edge to allow a rivet or bolt head or a rivet point to seat flush with or below the surface of the riveted or bolted object.

COUNTERWEIGHT: Weights that are mounted on the crankshaft opposite each crank throw. These weights reduce the vibration caused by putting the crank in practical balance and also reduce bearing loads due to inertia of moving parts.

COUPLING: A device for securing together adjoining ends of piping, shafting, and so forth, in such a manner to permit disassembly whenever necessary.

CRANE: A machine used for hoisting and moving pieces of material or portions of structures or machines that are either too heavy to be handled by hand or cannot be handled economically by hand.

CRANKCASE: The part of an engine frame which serves as a housing for the crank-shaft.

CRANKCASE SCAVENGING: Scavenging method that uses the pumping action of the power piston in the crankcase to pump scavenging air.

CRANKPIN: The portion of the crank throw attached to the connecting rod.

CRANKSHAFT: A rotating shaft for converting rotary motion into reciprocating motion.

CRANKSHAFT GEAR: The gear that is mounted to the crankshaft.

CRANK THROW: One crankpin with its two webs (the amount of offset of the rod journal).

CRANK WEB: The portion of the crank throw between the crankpin and main journal. This makes up the offset.

CREEP-RESISTANT ALLOY: A metal which resists the slow plastic deformation that occurs at high temperatures when the material is under constant stress.

CREST: The surface of the thread corresponding to the major diameter of an external thread and the minor diameter of an internal thread.

CRITICAL SPEED: The speed at which natural torsional vibrations of a crankshaft tend to reinforce themselves, causing vibration and potentially destructive stresses.

CROSS-CONNECT: To align systems to provide flow or to exchange energy between machinery groups.

CROSS-CONNECTED PLANT: A method of operating two or more plants as one unit from a common supply.

CYCLE: An interval of time during which a sequence of a recurring succession of events is completed.

CYLINDER: A solid figure with two circular bases. A hollow tube which contains the actions of combustion gases and the piston in an internal-combustion reciprocating engine.

CYLINDER BLOCK: A rigid unit of the engine frame which supports the engine’s cylinder liners and heads. A cylinder block may contain passages to allow circulation of cooling water and drilled lube oil passages.

CYLINDER LINER: A sleeve which is inserted in the bores of the engine block which make up the cylinder wall.

DAMPER: A device for reducing the motion or oscillations of moving parts.

DAMPING: (1) A characteristic of a system that results in dissipation of energy and causes decay in oscillations. (2) The negative feedback of an output rate of change.

DAY TANK: A fuel tank with the capacity to operate an engine for 24 hours. Also called SERVICE TANK.

DEAD CENTER: Either of the two positions when the crank and connecting rod are in a straight line at the end of the stroke.

DEAERATE: Process of removing dissolved oxygen.

DEAERATING FEED TANK (DFT): A unit in the steam-water cycle used to (1) free the condensate of dissolved oxygen, (2) heat the feed water, and (3) act as a reservoir for feed water.

DEGREE OF SUPERHEAT: The amount by which the temperature exceeds the saturation temperature.

DEHUMIDIFICATION: The mechanical process of removing water vapor from the air.

DENSITY: The weight per unit volume of a substance.

DENTAL COUPLING: A flexible coupling assembly, consisting of a set of external/internal gear teeth, that compensates for shaft misalignment between a driver and a driven machinery component.

DEPTH: The distance from the root of a thread to the crest, measured perpendicularly to the axis.

DESIGN PRESSURE (BOILER): The pressure specified by a manufacturer as a criterion in design. (In a boiler, it is approximately 103% of operating pressure.)

DESIGN TEMPERATURE: The intended operating temperature of the fresh water and lube oil at the engine outlet, at some specified rate of operation. The specified rate of operation is normal load.

DESUPERHEATED STEAM: Steam from which some of the superheat has been removed. DETONATION: Burning of a portion of the fuel in the combustion chamber at a rate faster than desired (knocking).

DIAL GAUGE OR INDICATOR: A precision micrometer-type instrument that indicates the reading by a needle moving across a dial face.

DIAPHRAGM: A dividing membrane or thin partition.

DIESEL CYCLE (ACTUAL): Combustion induced by compression ignition, begins on a constant-volume basis and ends on a constant-pressure basis.

DIESEL CYCLE (TRUE): Combustion induced by compression ignition, theoretically occurs at a constant pressure.

DIESEL ENGINE: An engine using the diesel or semi diesel cycle of operation; air alone is compressed and diesel fuel is injected before the end of the compression stroke. Heat of compression produces ignition.

DIFFUSER: (1) A duct of varying cross sections designed to convert a high-speed gas flow into low-speed flow at an increased pressure. (2) A device that spreads a fluid out in all directions and increases fluid pressure while decreasing fluid velocity.

DIRECT CURRENT (d.c.): An electric current that flows in one direction only.

DIRECT DRIVE: One in which the drive mechanism is coupled directly to the driven member.

DIRECTIONAL CONTROL VALVE: A valve which selectively directs or prevents flow to or from desired channels. Also referred to as selector valve, control valve, or transfer valve.

DISPLACEMENT: The volume of air or fluid which can pass through a pump, motor, or cylinder in a single revolution or stroke.

DISTILLATE: The product (fresh water) resulting from the condensation of vapours produced by the evaporation of seawater.

DISTILLATION: The process of evaporating seawater, then cooling and condensing the resulting vapours. Produces fresh water from seawater by separating the salt from the water.

DISTILLING PLANTS: Units commonly called evaporators used to convert seawater into fresh water.

DOUBLE REDUCTION: A reduction gear assembly that reduces the high input rpm to a lower output rpm in two stages.

DOUBLE SUCTION IMPELLER: An impeller with suction inlet on each side.

DRAWING: (1) Illustrated plans that show fabrication and assembly details. (2) The original graphic design from which a blueprint may be made. Also called plans.

DRAWING NUMBER: An identifying number assigned to a drawing, or a series of drawings.

DRUM, WATER: A tank at the bottom of a boiler. Also called mud drum.

DUPLEX STRAINER: A strainer containing two separate elements independent of each other.

DYNAMIC PRESSURE: (1) The pressure of a fluid resulting from its motion, equal to one-half the fluid density times the fluid velocity squared. (2) In incompressible flow, dynamic pressure is the difference between total pressure and static pressure.

ECONOMIZER: (1) A device provided in a carburettor to give the fuel-air mixture the richness required for high power. (2) A heat transfer device that uses the gases of combustion to preheat the feed water in the boiler before it enters the steam drum. See FEED HEATER.

EDUCTOR: A jet-type pump (no moving parts) which uses a flow of water to entrain and thereby pump water.

EFFICIENCY: The ratio of output power to input power, generally expressed as a percentage.

ELASTICITY: The ability of a material to return to its original size and shape.

ELBOW-ELL: A pipe fitting that makes an angle between adjacent pipes, always 90° unless another angle is stated.

ELECTRICAL ENERGY: Energy derived from the forced induction of electrons from one atom to another.

ELECTRODE: A metallic rod (welding rod), used in electric welding, that melts when current is passed through it.

ELECTROHYDRAULIC STEERING: A system having a motor-driven hydraulic pump that creates the force needed to actuate the rams to position the ship’s rudder.

ELECTROLYSIS: A chemical action that takes place between unlike metals in systems using seawater.

ELECTROLYTE: A solution of a substance which is capable of conducting electricity. An electrolyte may be in the form of either a liquid or a paste.

ELECTROMECHANICAL DRAWING: A special type of drawing combining electrical symbols and mechanical drawing to show the composition of equipment that combines electrical and mechanical features.

ELEMENT: (1) A substance which consists of chemically united atoms of one kind. (2) An indivisible part of a logic function or circuit. Fluidic elements are interconnected to form working circuits. (3) Parts of systems; for example, filter element, valve element, and so forth.

EMERGENCY: An event or series of events in progress which will cause damage to equipment unless immediate, timely, and correct procedural steps are taken.

EMULSIFIED OIL: A chemical condition of oil in which the molecules of the oil have been broken up and suspended in a foreign substance (usually water).

ENERGY: The capacity for doing work.

ENGINE: A machine which converts heat energy into mechanical energy.

ENGINEERING LOG: A legal record of important events and data concerning the machinery of a ship.

ENGINEER’S BELL BOOK: A legal record, maintained by the throttle watch, of all ordered main engine speed changes.

ENGINE ORDER TELEGRAPH: Electro-mechanical device which transmits orders concerning desired direction and general speed of the engines to the engine room. See ANNUNCIATOR.

ENGINE ORDER INDICATOR: A device on the ship’s bridge which transmits orders to the engine room for specific shaft speeds in revolutions per minute.

ENGINEERING OFFICER OF THE WATCH (EOOW): Officer on duty in the engineering spaces.

EPM (equivalent per million): A term used to describe the chemical concentration of dissolved material; used in reporting sample test results. It expresses the chemical equivalent unit weight of material dissolved in a million unit weights of solution. (The chemical equivalent weight of chloride is 35.5. If 35.5 pounds of chloride were dissolved in 1,000,000 pounds of water, the water would contain 1.00 ppm chloride).

EQUILIBRIUM: The state of balance between opposing forces or actions.

EVAPORATION: The action that takes place when a liquid changes to a vapour or gas.

EVAPORATOR: A distilling device to produce fresh water from seawater.

EXPANSION JOINT: (1) A junction in a piping system which allows for expansion and contraction. (2) A term applied to a joint which permits linear movement to take up the expansion and contraction due to changing temperature of ship movement.

EXPANSION TANK: Provides for expansion, overflow, and replenishment of cooling water in an engine.

EXPLODED VIEW: A pictorial view of a device in a state of disassembly, showing the appearance and interrelationship of parts.

EXTERNAL THREAD: A thread on the outside of a member (for example, a thread of a bolt).

FAHRENHEIT: The temperature scale using the freezing point as 32 and the boiling point as 212, with 180 equal divisions (degrees) between. FAIL: (1) The loss of control signal or power to a component. (2) The breakage or breakdown of a component or component part.

FATIGUE: The tendency of a material to break under repeated strain.

FEEDBACK: (1) A transfer of energy from the output circuit of a device back to its input. (2) Information about a process output which is communicated to the process input.

FEEDER: An electrical conductor or group of conductors between different generating and distributing units of a power system.

FEED HEATER: A heat transfer device that heats the feed water before it goes to the boiler.

FEEDWATER: Water that meets the requirements of Naval Ships’ Technical Manual, Chapter220, for use in a boiler.

FERROUS METAL: Metal with a high iron content.

FIELD WINDING. The coil used to provide the magnetizing force in motors and generators.

FILTER: A device through which gas or liquid is passed; dirt, dust, and other impurities are removed by the separating action.

FIRELINE: Section of piping and hose on discharge side of a proportioner leading to a fire location.

FIRE MAIN: The seawater line that provides firefighting and flushing water throughout the ship.

FIRING ORDER: The order in which the cylinders deliver their power stroke.

FIRING PRESSURE: The highest pressure reached in the cylinder during combustion.

FIRE TUBE BOILER: Boilers in which the gases of combustion pass through the tubes and heat the water surrounding them.

FLASHPOINT: The temperature at which a substance, such as an oil, will give off a vapour that will flash or burn momentarily when ignited.

FLEXIBLE COUPLING. A coupling that transmits rotary motion from one shaft to another while compensating for minor misalignment between the two units.

FLOOR PLATES: The removable deck plating of a fire room or engine room aboard ship. Also called deck plates.

FLOWMETER: An instrument used to measure quantity or the flow rate of a fluid motion.

FLUID: A substance capable of flowing or conforming to the shape of its container (a liquid or gas or mixture thereof).

FLYWHEEL: A heavy wheel attached to the crankshaft. It stores up energy during the power event and releases it during the remaining events of the operating cycle.

FLYWEIGHT: A governor; weights which move and assume positions in accordance with the speed of rotation.

FOAM NOZZLE: A nozzle designed to entrain air and mix it with water and foam liquid to produce a foam blanket.

FOOT-POUND: (1) The amount of work accomplished when a force of 1 pound produces a displacement of 1 foot. (2) The amount of torque produced by 1 pound of effort applied at a radius of 1 foot.

FORCE: The action of one body on another tending to change the state of motion of the body acted upon. Force is usually expressed in pounds.

FORCE-BALANCE: An arrangement of control system components using a mechanical force as the feedback signal. The feedback applied force must “null” the forces acting on a balanced mechanism.

FORCED FEED LUBRICATION: A lubrication system that uses a pump to maintain a constant pressure.

FREE FLOW: Flow which encounters negligible resistance.

FREQUENCY: The number of complete cycles per second (hertz) existing in any form of wave motion.

FRESH WATER: Water of relatively low dissolved solids content as compared to seawater. There are two types of shipboard fresh water: (1) feed water (the low-pressure drains of the steam generator condensate system), and (2) potable water (supplied from either a shore water source or a shipboard distilling plant).

FRESHWATER SYSTEM: A piping system which supplies fresh water throughout the ship.

FRICTION: The action of one body or substance rubbing against another, such as fluid flowing against the walls of a pipe; the resistance to motion caused by this rubbing.

FRICTION PRESSURE DROP: The decrease in the pressure of a fluid flowing through a passage attributable to the friction between the fluid and the passage walls.

FUEL MIXTURE: A ratio of fuel and air.

FUEL OIL SERVICE TANKS: Tanks from which the fuel oil service pumps take suction for supplying diesel fuel oil to the engine. See DAY TANKS.

FUEL TRANSFER PUMP: A mechanical device used to transfer fuel from the tank to the injection pump.

FUEL VALVE: A valve admitting fuel to the combustion chamber. In a more general sense, this term may also apply to any manual or automatic valve controlling the flow or fuel.

FULCRUM: The pivot point of a lever.

FULL-FLOATING PISTON PIN: A piston pin free to turn in the piston boss of the connecting rod eye.

FULL-FLOW OIL FILTER: A type of oil filter through which all engine oil passes before entering the lubrication channels.

FUSE: A protective device inserted in series with a circuit. It contains a metal that will melt or break when current is increased beyond a specific value for a definite period of time.

GAUGE GLASS: A device for indicating the liquid level in a tank.

GAUGE PRESSURE: Pressure above atmospheric pressure.

GALVANIZING: The process of coating one metal with another, ordinarily applied to the coating of iron or steel with zinc. The chief purpose of galvanizing is to prevent corrosion.

GAS: The form of matter that has neither a definite shape nor a definite volume.

GAS FREE: A term used to describe a space that has been tested and its atmosphere found safe for human occupation and for hot work (welding and cutting).

GASKET(S): (1) A class of material that provides a seal between two stationary parts. (2) Packing materials by which air, water, oil, or steam tightness is secured in such places as on doors, hatches, cylinders, manhole covers, or in valves, between the flanges of pipes, and so forth. Such materials as rubber, canvas, asbestos, paper, sheet lead and copper, soft iron, and commercial products are extensively used.

GEARING: A term applied to wheels which have teeth that mesh, engage, or gear with similar teeth or other wheels in such manner that motion given one wheel will be imparted to the other.

GENERATOR: A machine that converts mechanical energy into electrical energy.

GLAND SEALING: Water piped to a pump casing stuffing box to maintain a seal against air entering the pump casing.

GOVERNOR: A speed-sensitive device designed to control or limit the speed of the engine.

GRAPHITE: A crystalline form of carbon having a slippery feel and black colour with metallic lustre. Used for a lubricant.

GRAVITY HEAD: A supply of fluid above the suction level of a pump; also called “static head.”

GROUND PLUG: A three-pronged electrical plug used to ground portable tools to the ship’s structure. It is a safety device which always must be checked prior to your using portable tools.

HALIDE LEAK DETECTOR: A device that is used to locate leaks in refrigeration systems.

HANDHOLE: An opening large enough for the hand and arm to enter areas, such as the engine, for making slight repairs and for inspection purposes.

HARDENING: The treatment or heating and cooling (quenching) of metal to harden the surface.

HARDNESS: A quality exhibited by water containing various dissolved salts, principally calcium and magnesium. Hard water can deposit a heat transfer resistant scale on the heat exchanger surface.

HEAD: (1) A separate unit from the engine cylinder block designed to seal the cylinder at the combustion end. (2) The pressure or energy content of a hydraulic system, expressed in the height of a column of water in feet.

HEAT: A thermal form of energy.

HEAT EXCHANGER: Any device that is designed to allow the transfer of heat from one fluid (liquid or gas) to another.

HEATING SURFACE: The exposed surface of a heating unit in a heat exchanger which is directly exposed to the heat of the flue gases.

HEATING SYSTEM: A system for adding heat to maintain the desired air temperature, as distinguished from heat added incidentally or unavoidably.

HELICAL: A spiralling shape such as that made by a coil spring.

HELIX: The curve formed on any cylinder by a straight line in a plane that is wrapped around the cylinder with a forward progression.

HELM: (1) The term applied to the tiller, wheel, or steering gear, and also the rudder. (2) A mechanical device used to turn the rudder; usually a wheel aboard ship, or a lever (tiller) in boats.

HERTZ: The measurement of frequencies in cycles per second, 1 hertz being equal to 1 cycle per second.

HORSEPOWER (hp): A unit for measuring the power of motors or engines, equal to a rate of 33,000 foot-pounds per minute. The force required to raise 33,000 pounds at the rate of 1 foot per minute.

HOT WELL: A reservoir attached to the bottom of a condenser for collecting condensate.

HUMIDITY: The vapour content of the atmosphere. Humidity can vary depending on air temperature; the higher the temperature, the more vapour the air can hold.

HUNTING: A rhythmic variation of speed that can be eliminated by blocking the fuel supply manually or with load limit. The speed variation will reappear when the engine is returned to governor control.

HYDRAULICS: That branch of mechanics or engineering that deals with the action or use of liquids forced through tubes and orifices under pressure to operate various mechanisms.

HYDROCARBON: Chemical compound of hydrogen and carbon. All petroleum fuels are composed of hydrocarbons.

HYDROGEN: A highly explosive, light, invisible, non-poisonous gas. It is produced in small quantities when batteries are charged.

HYDROMETER: An instrument used to determine the specific gravities of liquids.

HYDROSTATIC: Static (non-moving) pressure generated by pressurizing liquid.

HYDROSTATIC TEST: A test using pressurized water to detect leaks in a closed system.

IGNITION, COMPRESSION: When the heat generated by compression in an internal-combustion engine ignites the fuel (as in a diesel engine).

IGNITION, SPARK: When the mixture of air and fuel in an internal-combustion engine is ignited by an electric spark (as in a gasoline engine).

IMPEDANCE: The total opposition offered to the flow of an alternating current. It may consist of any combination of resistance, inductive reactance, and capacitive reactance.

IMPELLER: An encased, rotating element provided with vanes, which draw in fluid at the centre and expel it at a high velocity at the outer edge.

IMPINGEMENT: The striking or hitting against an object with a clash or sharp collision, as air impinging upon the rotor of a turbine or motor.

IMPULSE LINES: Piping that connects a sensing element to the point at which it is desired to sense pressure, flow, temperature, etc.

INDICATED HORSEPOWER (ihp): The power transmitted to the pistons by the gas in the cylinders.

INDICATED THERMAL EFFICIENCY: The ratio of indicated horsepower to equivalent power input in the form of heat from fuel.

INDICATOR: An instrument for recording the variation of cylinder pressure during the cycle.

INDICATOR CARD: A graphical record of the cylinder pressures made by an indicator.

INDIRECT DRIVE: A drive mechanism coupled to the driven member by gears or belts.

INDUCTION: The act or process of producing voltages by the relative motion of a magnetic field across a conductor.

INERT: Inactive, such as gases that will not burn or support combustion.

INERTIA: The tendency of a body at rest to remain at rest, and a body in motion to continue to move at a constant speed along a straight line, unless the body is acted upon in either case by an unbalanced force.

INHIBITOR: Any substance which retards or prevents such chemical reactions as corrosion or oxidation.

INJECTION NOZZLE: A device which protrudes into the combustion chamber and delivers fuel to the cylinder.

INJECTION SYSTEM: A system designed to deliver fuel to the cylinder at the proper time and in the proper quantity under various engine loads and speeds.

IN-LINE ENGINE: An engine in which the cylinders are arranged in one straight line.

IN PHASE: Applied to the condition that exists when two waves of the same frequency pass through their maximum and minimum values of like polarity at the same instant.

INPUT SIGNAL: A pressure or flow of fluid that is directed into an input port to control an element or logic function.

INSULATION: A material used to retard heat transfer. A dielectric material which prevents the flow of electricity from an electric component.

INTAKE SYSTEM: Combination of components designed to supply air required for combustion.

INTEGRAL: Essential to completeness, as an integral part. (The valve stem is an integral part of the valve.)

INTERCOOLER: A device which cools a gas between the compression stages of a multiple stage compressor.

INTERFACE: Surface or area between abutting parts usually of different materials.

INTERNAL THREAD: A thread on the inside of a member (for example, the thread in-side a nut).

INVERSELY: Inverted or reversed in position or relationship.

INVERSE PROPORTION: The relation that exists between two quantities when an increase in one of them produces a corresponding decrease in the other.

ISOCHRONOUS GOVERNOR: A device that maintains the speed of the engine truly constant, regardless of the load.


ISOMETRIC PROJECTION: A set of three or more views of an object that appears rotated, giving the appearance of viewing the object from one corner. All lines are shown in their true length but angles are not accurately represented.

JACKBOX: A receptacle, usually secured to a bulkhead, in which telephone jacks are mounted.

JACKET: An outer case such as a water jacket or an insulated covering.

JACKET WATER: Water used as a coolant in the cooling system of an engine (usually chemically treated distilled water).

JACKING: Mechanically rotating an engine or reduction gear at very low speed.

JAM NUT: A second nut used on a bolt or stud to lock the holding nut. See LOCK NUT.

JOB ORDER: An order issued by a repair activity to its own subdivision to perform a repair job in response to a work request.

JOURNAL: Serves as the point of support and centre of rotation for the shaft. That part of a shaft that is prepared to accept a bearing (connecting rod, main bearing).

JUMPER: Any connecting pipe, hose, or wire normally used in emergencies aboard ship to bypass damaged sections of a pipe, hose, or wire. See BYPASS.

KELVIN SCALE: The temperature scale using absolute zero as the zero point and divisions that are the same size as Celsius degrees.

KEY: A small wedge or rectangular piece of metal inserted in a slot or groove between a shaft and a hub to prevent slippage.

KEYWAY: A slot cut in a shaft, pulley hub, wheel hub, and so forth. A square key is placed in the slot and engages a similar keyway in the mating piece. The key prevents slippage between the two parts.

KILO: A prefix meaning 1,000.

KINETIC ENERGY: The energy which a substance has while it is in motion.

LABYRINTH PACKING: A soft metal ring or rings arranged inside a casing throat in such a manner that the inside diametrical edges will form a series of seals along the surface of the rotating shaft. The edges fit either close to the surface of the shaft or in grooves machined in the shaft.

LAGGING: (1) A protective and confining cover placed over insulating material. (2) A term applied to the insulating material that is fitted on the outside of engine exhaust, piping, and so forth.

LAMBERT SEAL: The hydraulic equivalent of labyrinth packing.

LAP: To work two surfaces together with abrasives until a very close fit is produced; to polish.

LASH: The clearance or play between adjacent movable mechanical parts. See VALVE LASH.

LATENT HEAT: Heat that is given off or absorbed by a substance while it is changing its state.


The amount of heat (energy) required to change the state of a substance from a vapour to a liquid without a change in temperature.

LATENT HEAT OF VAPORIZATION: The amount of heat (energy) required to change the state of a substance from a liquid to a vapour without a change in temperature.

LEAD: (1) The distance a screw thread advances in one turn, measured parallel to the axis. On a single-thread screw, the lead and the pitch are identical; on a double-thread screw, the lead is twice the pitch; on a triple-thread screw, the lead is three times the pitch. (2) A wire or connection.

LIFT CHECK VALVE: A valve having a guide-mounted, spring-loaded disk wherein liquid exerting pressure on the bottom of the disk will lift the disk and pass through. Pressure against the top of the disk shuts the disk and ensures only one direction of flow.

LIGHT OFF: To start; literally, to start a fire in, such as to light off a boiler.

LIMIT SWITCH: A switch that is actuated by the mechanical motion of an element.

LIQUID: A form of matter that has a definite volume but takes the shape of its container.

LOAD: (1) External resistance overcome by a prime mover. (2) The power that is being delivered by a generator.

LOADING: The act of transferring energy into or out of a system.

LOCAL MANUAL OPERATION: Direct manual positioning of a control valve or power operator by means of a hand wheel or lever.

LOCKED TRAIN: A gear arrangement that has each high-speed (prime mover) pinion “locked” between two primary gears which cancel the tooth loading on the pinion bearings.

LOCK NUT: (1) A thin nut that is turned down over the regular nut on a bolt to lock the regular nut against turning off. (See JAM NUT.) (2) A thin nut placed on a pipe to hold packing at a joint or used on both sides of a bulkhead through which a pipe passes to secure tightness.

LOG: (1) A ship’s speedometer. (2) The act of a ship in making a certain speed, as “The ship logged 20 knots.” (3) A book or ledger in which the watch officer records data or events that occurred during the watch.

LOG BOOK: Any chronological record of events, such as the engineering watch log.

LOG ROOM: Engineer’s office aboard ship. LOOP SEAL: A vertical U-bend in drain piping in which a water level is maintained to create an airtight seal.

LUBE OIL PURIFIER: A unit that removes water and sediment from lubricating oil by centrifugal force.

LUBRICANT: Any material, usually of a petroleum nature, such as grease, oil, and so forth that is placed between two moving parts in an effort to reduce friction.

LUG: An earlike projection that is frequently split, such as the clamping lug on the tailstock of a lathe.

MACHINABILITY: The ease with which a metal may be turned, planed, milled, or other-wise shaped.

MACHINE FINISH: Operation of turning or cutting an amount of stock from the surface of metal to produce a finished surface.

MAGNETIC FIELD: The space in which a magnetic force exists.

MAGNETO: A generator that produces alternating current and has a permanent magnet as its field.

MAIN CONDENSER: A heat exchanger that converts exhaust steam to feed water.

MAIN DRAIN SYSTEM: System used for pumping bilges; consists of pumps and associated piping.

MAIN INJECTION (SCOOP INJECTION): An opening in the skin of a ship designed to deliver cooling water to the main condenser by the forward motion of the ship.

MAJOR DIAMETER: The largest diameter of an internal or external thread.

MALLEABILITY: That property of a material which enables it to be stamped, hammered, or rolled into thin sheets.

MANIFOLD: (1) A fitting or header that receives exhaust gases from several cylinders. (2) A fitting that has several inlets or outlets to carry liquids or gases.

MAXIMUM OPERATING PRESSURE: The highest pressure that can exist in a system or subsystem under normal operating conditions.

MAXIMUM SYSTEM PRESSURE: The highest pressure that can exist in a system or sub-system during any condition.

MEAN EFFECTIVE PRESSURE (MEP): The calculated combustion in pounds per square inch (average) during the power stroke, minus the pounds per square inch (average) of the remaining three strokes.

MEAN INDICATED PRESSURE (MIP): The net mean gas pressure acting on the piston to produce work.

MECHANICAL ADVANTAGE (MA): The advantage (leverage) gained by the use of devices, such as wheels, to open large valves and chain falls; blocks and tackles to lift heavy weights; and wrenches to tighten nuts on bolts.

MECHANICAL CLEANING: A method of cleaning the firesides of boilers by scraping and wire brushing.

MECHANICAL CYCLE: The number of piston strokes occurring during any one series of events (for example, 2-stroke or 4-stroke cycle).

MECHANICAL DRAWING: Scale drawings of mechanical objects. (See DRAWING.)

MECHANICAL EFFICIENCY: (1) The ratio of brake horsepower to indicted horsepower, or ratio of brake mean effective pressure to mean indicated pressure. (2) An engine’s rating, which indicates how much of the potential horsepower is wasted through friction within the moving parts of the engine.

METERING: Accurate measuring of the fuel for the same fuel setting where exactly the same quantity of fuel will be delivered to each cylinder for each power stroke of the engine.

MHO: The unit of conductance; the reciprocal of an ohm.

MICRO: A prefix meaning one millionth.

MICROMHO: Electrical unit used with salinity indicators for measuring the conductivity of water.

MILLI: A prefix meaning one-thousandth.

MONITORING POINT: The physical location at which any indicating device displays the value of a parameter at some control station. See PARAMETER.

MOTOR: (1) A rotating machine that transforms electrical energy into mechanical energy. (2) An actuator which converts fluid power to rotary mechanical force and motion.

MOTOR CONTROLLER: A device (or group of devices) that governs, in some predetermined manner, the operation of the motor to which it is connected.

MOTOR GENERATOR SET: A machine consisting of a motor mechanically coupled to a generator and usually mounted on the same base.

NAVAL DISTILLATE DIESEL FUEL: The fuel normally used in diesel engines. The most commonly used for boilers and diesel engines is naval distillate (NATO symbol F-76), but other fuels such as JP-5 (NATO symbol F-44) and naval distillate lower pour point (NATO symbol F-75) are also used.

NEEDLE VALVE: Type of valve with a rod-shaped, needle-pointed valve body which works into a valve seat so shaped that the needle point fits into it and closes the passage. Suitable for precise control of flow.

NEGATIVE CHARGE: The electrical charge carried by a body which has an excess of electrons.

NEOPRENE: A synthetic rubber highly resistant to oil, light, heat, and oxidation.

NIGHT ORDER BOOK: A notebook containing standing and special instructions from the engineering officer to the engineering officers of the night watches.

NIPPLE: A piece of pipe that has an outside thread at both ends for use in making pipe connections. Various names are applied to different lengths, such as close, short, long, and so forth.

NITROGEN: An inert gas which will not support life or combustion.

NOMINAL OPERATING PRESSURE: The approximate pressure at which an essentially constant-pressure system operates. This pressure is used for the system’s basic pressure identification.

NONFERROUS METAL: Metal that is composed primarily of a metallic element, or elements other than iron.

NORMALIZE: To heat steel to a temperature slightly above its critical point and then allow it to cool slowly in air.

NOZZLE: A taper or constriction used to speed up or direct the flow of gas or liquid.

NOZZLE AREA: Smallest opening (area) of a nozzle that is at a right angle to the direction of flow.

OCCUPATIONAL STANDARDS: Requirements that describe the work of each Navy rating.

OFFSET SECTION: A section view of two or more planes in an object to show features that do not lie in the same plane.

OHM: The unit of electrical resistance.

OHMMETER: An instrument for directly measuring resistance in ohms.

OIL KING: A petty officer who receives, transfers, discharges, and tests fuel oil and maintains fuel oil records.

OIL STRAINER: A strainer placed at the inlet end of the oil pump to prevent dirt and other particles from getting into moving parts.

OILTIGHT: Having the property of resisting the passage of oil.

ONBOARD PLANS: See SHIP’S PLANS.OPERATING CHARACTERISTICS: The combination of a parameter and its set points. See PARAMETER.

OPERATING PRESSURE: The constant pressure at which a component is designed to operate in service.

OPERATING TEMPERATURE: The actual temperature of a component during operation.

OPERATION (AUTOMATIC): The regulation of a process by a controlling system without manual intervention.

OPERATION (LOCAL-MANUAL): Positioning of a final control element by attending personnel from the element’s manual control station.

ORIFICE: A circular opening in a flow passage which acts as a flow restriction.

OSCILLATION: A backward and forward motion; a vibration.

OTTO COMBUSTION CYCLE: Combustion induced by spark ignition occurring at constant volume. The basic combustion cycle of a gasoline engine.

OUTPUT SIGNAL: The pressure or flow of fluid leaving the output port of a fluidic device.

OVERHAUL: To inspect, repair, and put in proper condition for operation.

OVERLOAD: A load greater than the rated load of an engine or electrical device.

OXIDATION: The process of various elements and compounds combining with oxygen. The corrosion of metal is generally a form of oxidation; rust on iron, for example, is iron oxide or oxidation.

OXYGEN-FREE FEEDWATER: Water from which dissolved oxygen has been removed.

PACKING: A class of seal that provides a seal between two parts of a unit, which move in relation to each other.

PANT, PANTING: A series of pulsations caused by minor, recurrent explosions in the firebox of a ship’s boiler. Usually caused by a shortage of air.

PARALLEL CIRCUIT: An electrical circuit with two or more resistance or impedance units connected to split the current flow through both units at the same time.

PARALLEL OPERATION: Two or more units operating simultaneously and connected so their output forms a common supply, as opposed to series or independent operation.

PARAMETER: A variable such as temperature, pressure, flow rate, voltage, current, frequency, etc., which may be indicated, monitored, checked or sensed in any way during operation or testing.

PARTIAL SECTION: A sectional view consisting of less than a half-section. Used to show the internal structure of a small portion of an object. Also known as broken section.

PARTICULATE: Minute particles or quantities of solid matter resulting from incomplete combustion. Carbon, sulphur, ash, and various other compounds are all referred to as particulate, either collectively or individually, when discharged into a flue or into the atmosphere.

PERIPHERY: (1) The curved line which forms the boundary of a circle (circumference), ellipse, or similar figure. (2) The outside surface, especially that of a rounded object or body.

pH: A chemistry term that denotes the degree of acidity or alkalinity of a solution. The pH of water solution may have any value between 0 and 14. A solution with a pH of 7 is neutral. Above 7, it is alkaline; below 7, it is acidic.

PHANTOM VIEW: A view showing the alternate position of a movable object, using a broken line convention.

PHASE: An impulse of alternating current. The number of phases depends on the generator windings. Most large generators produce a 3-phase current that must be carried on at least three wires.

PHYSICAL CHANGE: A change that does not alter the composition of the molecules of a substance, such as from gas to liquid.

PICTORIAL DRAWING: A drawing which gives the real appearance of an object showing general location, function, and appearance of parts and assemblies.

PILOT VALVE: A small valve disk and seat, usually located within a larger disk, which controls the operation of another valve or system.

PILOT VALVE (GOVERNOR): A hydraulic control valve that regulates hydraulic pressure to a piston and cylinder.

PINION: A gear that meshes with a larger gear.

PINTLE-TYPE NOZZLE: A closed-type nozzle having a projection on the end of the fuel valve which extends into the orifice when the valve is closed.

PIPE: A tube or hollow body for conducting a liquid or gas. Dimensions of a pipe are designated by nominal (approximate) outside diameter (OD) and wall thickness.

PIPING: An assembly of pipe or tubing, valves, and fittings that forms the transferring part of a system.

PISTON: A cylindrical plug which slides up and down in the cylinder and which is connected to the connecting rod.

PISTON BOSS: The reinforced area around the piston-pin bore.

PISTON DISPLACEMENT: The volume of air moved or displaced by a piston as the piston moves from BDC to TDC.

PISTON HEAD: The portion of the piston above the top ring.

PISTON LANDS: The spaces in pistons between the ring grooves.

PISTON PIN (WRIST PIN): A cylindrical alloy pin that passes through the piston bore and connects the connecting rod to the piston.

PISTON RING: A split ring of the expansion type placed in a groove of the piston to seal the space between the piston and the wall.

PISTON-RING END GAP: The clearance between the ends of a piston ring.

PISTON-RING GROOVE: The grooves cut in the piston into which the piston rings are fitted.

PISTON-RING SIDE CLEARANCE: The clearance between the sides of the ring and the ring lands.

PISTON SKIRT: The portion of the piston that is below the piston bore.

PISTON SPEED: The total distance travelled by each piston in one minute.

PITCH: A term applied to (1) the distance a propeller will advance during one revolution; (2) the distance between the centres of the teeth of a gear wheel; (3) the axial advance of one convolution of the thread on a screw; and (4) the spacing of rivets, and so forth.

PITTING: The localized corrosion of iron and steel in spots, usually caused by irregularities in surface finish and resulting in small in-dentations or pits.

PLAN VIEW: A view of an object or area as it would appear from directly above.

PLUG COCK: A valve that has a rotating plug, which is drilled for the passage of fluid.


PNEUMATIC: Driven, or operated, by air pressure.

PNEUMATICS: That branch of physics pertaining to the pressure and flow of gases.

POLAR TIMING DIAGRAM: A graphic method of illustrating the events of an engine cycle with respect to crankshaft rotation. (See figures 2-1 and 2-2.)

PORT SCAVENGING: Introducing scavenging air through ports in the cylinder wall when they are uncovered by the piston near the end of the power stroke.

POTABLE WATER: Water that is suitable for drinking. The potable water system supplies scuttlebutts, sinks, showers, sculleries, and galleys, as well as provides makeup water for various freshwater cooling systems.

POTENTIAL: The amount of charge held by a body as compared to another point or body. Usually measured in volts.

POTENTIAL ENERGY: (1) Energy at rest; stored energy. (2) The energy a substance has because of its position, its condition, or its chemical composition.

POWER: The rate of doing work or the rate of expending energy. The unit of electrical power is the watt; the unit of mechanical power is horsepower.

PPM (PARTS PER MILLION): Concentration of the number of parts of a substance dissolved in a million parts of another substance. Used to measure the salt content of water. If 1 pound of sea salt were dissolved in l,000,000 pounds of water, the sea salt concentration would be 1.00 ppm.

PRECISION INSERT BEARING: A precision type of bearing consisting of an upper and lower shell.

PRECOMBUSTION CHAMBER: A portion of the combustion chamber connected to the cylinder through a narrow throat. Fuel is injected into and is partly burned in the pre-combustion chamber. Heat released by this partial burning causes the contents of the pre-combustion chamber to be ejected into the cylinder with considerable turbulence.

PRESSURE: The amount of force distributed over each unit of area. Pressure is expressed in pounds per square inch (psi), atmospheric units, or kilograms per square centimetre, inches of mercury, and other ways.

PRESSURE DIFFERENTIAL: The difference in pressure between any two points of a system or a component.

PRESSURE RELIEF VALVE: A valve designed to open when pressure in the system exceeds a certain limit.

PRESSURE SWITCH: An electrical switch operated by the increase and decrease of pressure.

PRESSURE-TIME FUEL SYSTEM: A system in which fuel is injected into the cylinders at a specific pressure in separately timed events.

PRIMARY SENSING ELEMENT: The control component that transforms energy from the controlled medium to produce a signal which is a function of the value of the controlled variable.

PRIME MOVER: (1) the source of motion- as a diesel engine. (2) The source of mechanical power used to drive a pump or compressor. (3) The source of mechanical power used to drive the rotor of a generator.

PRIMING: To fill, load, or put in working order (to fill a fuel system with fuel or a pump with water).

PROMPTNESS: The time it takes a governor to move the fuel control from a no load position to a full load position.

PROPELLER: A propulsive device consisting of a boss or hub carrying two or more radial blades. Also called a SCREW.

PROPELLER ARCH: The arched section of the stern frame above the propeller.

PROPELLER GUARD: A framework fitted somewhat below the deck line on narrow, high-speed vessels with large screws, designed to overhang and thus protect the tips of the propeller blades.

PROPELLER THRUST: The effort delivered by a propeller in pushing a vessel ahead.

PROPULSION PLANT: The entire propulsion plant or system, including prime movers and those auxiliaries essential to their operation.

PSYCHROMETER: A form of hygrometer consisting of a wet and a dry bulb thermometer.

PULSATION: A rhythmical throbbing or vibrating.

PUMP: (1) A device which converts mechanical energy into fluid energy. (2) A device that raises, transfers, or compresses fluids or gases.

PUMP CAPACITY: The amount of fluid a pump can move in a given period of time, usually stated in gallons per minute (gpm).

PUMP RISER: The section of piping from the pump discharge valve to the piping main.

PURGE: To make free of an unwanted substance (as to bleed air out of a fuel system).

PURPLE-K-POWDER (PKP): A purple powder composed of potassium bicarbonate that is used on class B fires. Can be used on class C fires; however, CO2 is a better agent for such electrical fires because it leaves no residue.

PYROMETER: A device for measuring high temperatures such as the exhaust temperature of an internal-combustion engine.

RACE (bearing): The inner or outer ring that provides a contact surface for the balls or rollers in a bearing.

RADIAL BEARINGS: Bearings designed to carry loads applied in a plant perpendicular to the axis of the shaft and used to prevent movement in a radial direction.

RADIAL THRUST BEARINGS: Bearings designed to carry a combination of radial and thrust loads. The loads are applied both radially and axially with a resultant angular component.

RADIANT HEAT: Heat transferred without physical contact between the emitting region and the receiving region.

RADIUS: A straight line from the centre of a circle or sphere to its circumference or surface.

RAM TYPE CYLINDER: A fluidic actuating cylinder in which the cross-sectional area of the piston rod is more than one-half the cross-sectional area of the movable piston-like element. The piston used is also referred to as a PLUNGER.

RATE ACTION: That action of a control system component whose output is proportional to the rate of change in its input for slowly changing signals and proportional to the input for rapidly changing signals.

RATIO: The value obtained by dividing one number by another, indicating their relative proportions.

RAW WATER: Untreated water used for cooling.

REACH ROD: A length of pipe or bar stock used as extension on valve stems.

RECEIVER: (1) A container in which compressed gas is stored to supply pneumatic power. (2) A reservoir for pressure refrigerant.

RECEIVER INDICATOR: Pressure-sensitive instrument indicating the loading pressure signals in percentage.

RECIPROCATING: Moving back and forth, as a piston reciprocating in a cylinder.

REDUCER: (1) Any coupling or fitting that connects a large opening to a smaller pipe or hose. (2) A device that reduces pressure in a fluid (gas or liquid) system.

REDUCING STATION: An assembly consisting of a reducing valve, isolation valves, and bypass valves for the reducer.

REDUCING VALVES: Automatic valves that provide a steady pressure lower than the supply pressure.

REDUCTION GEAR: An arrangement of shafts and gears such that the number of revolutions of the output shaft is less than that of the input shaft-generally used between a prime mover and the propeller shaft.

REEFER: (1) A provision cargo ship or a refrigerated compartment. (2) An authorized abbreviation for refrigerator.

REFRIGERANT 12 (R-12): A gas used in air conditioning and refrigeration systems. One of a series of fluorocarbon refrigerants.

REFRIGERATION TON: Unit of measure for the amount of heat removed, equal to 12,000 Btu per hour.

REGULATOR (gas): An instrument that controls the flow of gases from compressed gas cylinders.

RELATIVE HUMIDITY: The ratio of the weight of water vapour in a quantity of air to the weight of water vapour which that quantity of air would hold if saturated at the existing temperature. Usually expressed as a percentage; for example, if air is holding half the moisture it is capable of holding at the existing temperature, the relative humidity is 50%.

RELAY: A magnetically operated switch that makes and breaks the flow of current in a circuit.

RELIEF VALVE: A pressure control valve used to limit system pressure.

REMOTE OPERATING GEAR: Flexible cables or shafts attached to valve wheels so the valves can be operated from another compartment.

RESERVOIR: A container which serves primarily as a supply source of the liquid for a hydraulic system.

RESISTANCE: The opposition to the flow of current caused by the nature and physical dimensions of a conductor.

RESPONSE TIME: The time lag between a signal input and the resulting change of output.

RESTRICTION: A reduced cross-sectional area in a line or passage which reduces the rate of flow.

RETURN LINE: A line used for returning fluid to the reservoir or atmosphere.

RHEOSTAT: A variable resistor. Similar in function and construction to a potentiometer.

RISER: A vertical pipe leading off a large one; for example, a fire main line.

ROCKER ARM: Part of the valve actuating mechanism of a reciprocating engine.

ROOT: The surface of the thread corresponding to the minor diameter of an external thread and the major diameter of an internal thread.

ROOT VALVE: A valve located where a branch line comes off the main line.

ROTOR: The rotating element of a motor, pump, or turbine.

RUDDER STOCK: A vertical shaft that has a rudder attached to its lower end and a yoke, quadrant, or tiller fitted to its upper portion by which it may be turned.

RUDDER STOPS: Fittings attached to the ship structure or to shoulders on the rudder post to limit the swing of the rudder.

SAFETY VALVE: An automatic, quick opening and closing valve that has a reset pressure lower than the lift pressure.

SALINE/SALINITY: (1) Constituting, or characteristic of, salt. (2) Relative salt content of water.

SALINOMETER: A hydrometer that measures the concentration of salt in a solution.

SATURATED AIR: Air that attains the maximum amount of moisture it can hold at a specified temperature.

SATURATED STEAM: Steam at the saturation temperature.

SATURATION PRESSURE: The pressure corresponding to the saturation temperature.

SATURATION TEMPERATURE: The temperature at which a liquid boils under a given pressure. For a given pressure there is a corresponding saturation temperature.

SAY BOLT VISCOSIMETER: An instrument that determines the fluidity or viscosity (resistance to flow) of an oil.

SCALE: Undesirable deposit, mostly calcium sulphate, which forms in the tubes of boilers.

SCAVENGING AIR: Increased amount of air available as a result of blower action used to fill an engine cylinder with a fresh charge of air and, during the process, to aid in clearing the cylinder of the gases of combustion.

SCHEMATIC DIAGRAM: A diagram using graphic symbols to show how a circuit functions electrically.


SEA CHEST: An arrangement for supplying seawater to engines, condensers, and pumps and for discharging waste water from the ship to the sea. It is a cast fitting or a built-up structure located below the waterline of the vessel and having means for attachment of the piping. Suction sea chests are fitted with strainers or gratings.

SEA COCK, SEA CONNECTION: A sea valve secured to the plating of the vessel below the waterline for use in flooding tanks, magazines, and so forth, to supply water to pumps and for similar purposes.

SEAWATER: The water in the sea. Seawater is an aqueous solution of various minerals and salts (chlorides). In suspension also, but not dissolved in the water, may be various types of vegetable and animal growths, including, in many cases, bacteria and organisms harmful or actually dangerous to health.

SECTION: A view showing internal features as if the viewed object had been cut or sectioned.

SEDIMENT: An accumulation of matter that settles to the bottom of a liquid.

SENSIBLE HEAT: Heat that is given off or absorbed by a substance without changing its state.

SENSING POINT: (1) The physical and/or functional point in a system at which a signal may be detected and monitored or may cause some automatic operation to result. (2) Where parameters are determined.

SENSITIVITY: The change in speed required before the governor will make a corrective movement.

SENSOR: A component that senses physical variables and produces a signal to be observed or to actuate other elements in a control system. Temperature, sound, pressure and position sensors are examples.

SENTINEL VALVE: A relief valve designed to emit an audible sound; does not have substantial pressure-relieving capacity.

SEPARATOR: A trap for removing oil and water from compressed gas before it can collect in the lines or interfere with the efficient operation of pneumatic systems.

SERVICE TANKS: Tanks in which fluids for use in the service systems are stored. Also DAY TANK.

SERVO: A device used to convert a small movement into a greater movement or force.

SET POINT: The level or value at which a controlled variable is to be maintained.

SETSCREW: A machine screw with a slotted, allen, or square head used to hold a part in place.

SHAFT ALLEY: A watertight passage, housing the propeller shafting from the engine room to the bulkhead at which the stern tube commences.

SHAFT/SHAFTING: The cylindrical forging, solid or tubular, used for transmission of rotary motion from the source of power, the engine, to the propellers.

SHIM: A thin layer of metal or other material used to true up a machine or inserted in bearings to permit adjustment after wear of the bearing.

SHIP’S PLANS: A set of drawings of all significant construction features and equipment of a ship, as needed to operate and maintain the ship. Also called ONBOARD PLANS.

SHORE WATER: A broad term for classifying water originating from a source ashore.

SHUTOFF VALVE: A valve which operates fully open or fully closed.

SIMPLEX PUMP: A pump that has only one liquid cylinder.

SLEEVE: A casing fitted over a line or shaft for protection against wear or corrosion.

SOLENOID: An electromagnetic coil that contains a movable plunger.

SOLID COUPLING: A device that joins two shafts rigidly.

SOUNDING PIPE OR SOUNDING TUBE: A vertical pipe in an oil or water tank, used to guide a sounding device during measurement of the depth of liquid in the tank.

SPECIFIC GRAVITY: The ratio of the weight of a given volume of any substance to the weight of an equal volume of distilled water. Since the distilled water weighs approximately 62.4 pounds per cubic foot, any substance which weighs less than this has a specific gravity of less than one and will float on water. Any substance of greater weight per cubic foot has a specific gravity of more than one and will sink. Specific gravity of gases is based in a like manner on the weight of air.

SPECIFIC HEAT: The amount of heat required to raise the temperature of 1 pound of a substance 1°F. All substances are compared to water, which has a specific heat of 1 Btu/lb/°F.

SPEED DROOP: A progressive drop in speed as load is picked up by the prime mover from no load to full load without manually changing the speed setting.

SPEED-LIMITING GOVERNOR: A device for limiting the speed of a prime mover.

SPEED-REGULATING GOVERNOR: A device that maintains a constant speed on an engine that is operating under varying load conditions.

SPLIT PLANT: A method of operating propulsion plants so that they are divided into two or more separate and complete units.

SPRING BEARINGS: Bearings positioned at varying intervals along a propulsion shaft to help keep it in alignment and to support its weight.

STABILITY: The ability of a governor to correct a speed disturbance with a minimum of corrective motions.

STANDBY EQUIPMENT: Two auxiliaries that perform one function. When one auxiliary is running, the standby is so connected that it may be started if the first fails.

STATOR: The stationary element of a motor or generator.

STEAM: Vapour of water; invisible, odourless, tasteless, and usually under greater than atmospheric pressure.

STEERING ENGINE: The machinery that turns the rudder.

STEERING GEAR: A term applied to the steering wheels, leads, steering engine, and fittings by which the rudder is turned.

STEP-TOOTHED LABYRINTH: Labyrinth type packing having each alternate tooth ring installed on the shaft and running in close proximity to the fixed packing ring.

STERN TUBE: (1) The bearing supporting the propeller shaft where it emerges from the ship. (2) A watertight enclosure for the propeller shaft.

STERN TUBE FLUSHING WATER: Water circulated through the stern tube from in-board to prevent accumulation of debris in the stern tube while the ship is at rest or backing down.

STUFFING BOX: A device to prevent leakage between a moving and a fixed part.

SUMP: A container, compartment, or reservoir used as a drain or receptacle for engine oil.

SUPERCHARGE: To supply a charge of air at a pressure higher than that of the surrounding atmosphere.

SUPERCHARGER: A device for increasing the volume of the air charge of an internal-combustion engine.

SUPERHEAT: Amount of heat applied to vapour to raise its temperature above the saturation temperature, while maintaining constant pressure.

SUPPLY AIR: Compressed air required for the proper operation of pneumatic control components.

SURGING: A rhythmic variation of speed of an engine, which can be eliminated by blocking the fuel supply manually or with load limit, and which will not reappear when returned to governor control unless the speed adjustment is changed or the load changes.

SWING CHECK VALVE: A valve that has a guide-mounted disk swung from the top by a horizontal pin. A liquid exerting pressure against the disk will cause it to open, allowing a flow. Pressure exerted in the opposite direction will close the valve, ensuring only one direction of flow.

SWITCHBOARD: A panel or group of panels with automatic protective devices, used to distribute the electrical power throughout the ship.

SYNCHRONIZE: (1) To make two or more events or operations occur at the proper time with respect to each other. (2) To adjust two engines to run at the same speed.

SYNTHRON SEAL: A rubber strip seal installed on the shaft to prevent seawater from leaking into the ship along the shaft.

TACHOMETER: An instrument for indicating revolutions per minute.

TAIL SHAFT: The aft section of the shaft that receives the propeller.

TAKE LEADS: A method of determining bearing and other clearances. Mostly replaced by other methods such as plastigage and bearing shell thickness measurements.

TDC (TOP DEAD CENTER): The position of a reciprocating piston at its uppermost point of travel.

TEFLON: A plastic with excellent self-lubricating bearing properties.

TELEGRAPH: An apparatus, either electrical or mechanical, for transmitting orders, as from a ship’s bridge to the engine room, steering gear room, or elsewhere about the ship.

TELEMOTOR: A device for operating the steering engine from the pilothouse by means of either fluid pressure or electricity.

TEMPER: To harden steel by heating and sudden cooling by immersion in oil, water, or other coolant.

TENSILE STRENGTH: The measure of a material’s ability to withstand a tensile, or pulling, stress without rupture, usually measured in pounds or tons per square inch of cross section.

THERMAL ENERGY: Energy contained in or derived from, heat.

THERMAL EXPANSION: The increase in volume of a substance due to temperature change.

THERMOCOUPLE: (1) A bimetallic device capable of producing an electromotive force roughly proportional to temperature differences on its hot and cold junction ends and used in the measurement of elevated temperatures. (2) A junction of two dissimilar metals that produces a voltage when heated.

THREAD: The spiral part of a screw.

THROAT: Opening in the cylinder block through which the crankshaft end is extended.

THROTTLEMAN: Person in the engine room who operates the throttles to control the main engines.

THROTTLE VALVE: A type of valve especially designed to control rate of flow.

THROTTLING: Operating a valve partially open to produce a pressure drop with flow.

THRUST BEARINGS: Bearings that limit the axial (longitudinal) movement of the shaft.

TILLER: An arm attached to the rudder head for operating the rudder.

TIMING GEARS: Gears attached to the crankshaft, camshaft, idler shaft, or injection pump to provide a means to drive the camshaft and injection pump and to regulate the speed and performance.

TOLERANCE: The amount that a manufactured part may vary from its specified size.

TORQUE: A force or combination of forces that produces or tends to produce a twisting or rotary motion.

TOUGHNESS: The property of a material that enables it to withstand shock as well as to be deformed without breaking.

TRANSDUCER: A device that converts signals received in one medium into outputs in some other medium; for example, electrical inputs to fluidic outputs.

TRANSFER VALVE: A manually operated direction valve used to switch automatic control systems from automatic to manual operation and vice versa.

TRANSFORMER: A device composed of two or more coils, linked by magnetic lines of force, used to transfer energy from one circuit to another. Also, an electrical device used to step up or step down an a.c. voltage.

TRANSMISSION: A device that transmits power from the engine (driving unit) to the load (driven unit).

TRICK WHEEL. A steering wheel in the steering engine room or emergency steering station of a ship, used in case of emergency.

TUBING: That type of fluid line the dimensions of which are designated by actual measured outside diameter (OD) and by actual measured wall thickness.

TURBINE: (1) A rotary motor actuated by the reaction, impulse, or both, of a flow of pressurized fluid. A turbine usually consists of a series of curved vanes on a centrally rotating shaft. (2) A multibladed rotor, driven by steam, hot gas, or water.

TURBULENCE: Air in the combustion space in motion.

UNBURNABLE OIL: That quantity of oil below the stripping suction in storage tanks and below the service suction in service tanks.

UNIT INJECTOR: A diesel engine injector that combines a pump and a fuel-spray nozzle in a single unit.

UNSTABLE: That action of an automatic control system and controller process that is characterized by a continuous cycling of one or more system variables for a degree greater than a specified maximum.

VACUUM: Pressure less than atmospheric pressure.

VALVE: A mechanism that can be opened or closed to control or stop the flow of a liquid, gas, or vapour from one place to another place.

VALVE GUIDE: A hollow-sized shaft pressed into the cylinder head to keep the valve in proper alignment.

VALVE KEEPER (VALVE RETAINER): A device designed to lock the valve-spring retainer to the valve stem.

VALVE LASH: Clearance between the top of the valve stem and the valve-lifting mechanism.

VALVE LIFT: The distance a valve moves from the fully closed to the fully open position.

VALVE OVERLAP: The period of crankshaft rotation during which both the intake and exhaust valves are open. It is measured in degrees.

VALVE ROTATOR: A mechanical device locked to the end of the valve stem that forces the valve to rotate about 5° with each rocker-arm action.

VALVE SEAT: The surface, normally curved, against which the valve disk’s operating face comes to rest to provide a seal against leakage of liquid, gas, or vapour.

VALVE SEAT INSERT: Metal ring inserted into a valve seat, made of a special metal that can withstand operating temperature satisfactorily.

VALVE SPRING: The compression-type spring that closes the valve when the valve-operating cam assumes a closed-valve position.

VAPOR: The gaseous state of a substance that is usually a liquid or solid at atmospheric temperature and pressure.

VARIABLE DISPLACEMENT: The type of pump or motor in which the volume of fluid delivered per cycle can be varied.

VELOCITY: The rate of motion in a particular direction. The velocity of fluid flow is usually measured in feet per second.

VENT: A valve in a system used primarily to permit air to escape.

VENTILATION SYSTEM: A system that removes heat and stale air and provides fresh air by means of mechanical or natural distribution ductwork. The system may also include filters and heaters.

VENTURI: A tube that has a narrowing throat or constriction to increase the velocity of fluid flowing through it. The flow through the venturi causes a pressure drop in the smallest section.

VIEW: A drawing of a side or plane of an object as seen from one point.

VISCOSITY: The internal resistance of a fluid that tends to prevent it from flowing.

VITAL CIRCUITS: Electrical circuits that provide power or lighting to equipment and spaces necessary for propulsion, ship control, and communications.

VOID: An empty tank.

VOLATILE: The term that describes a liquid that vaporizes quickly.

VOLT: The unit of electrical potential.

VOLTAGE TESTER. A portable instrument that detects electricity.

VOLTMETER: An instrument designed to measure a difference in electrical potential in volts.

VOLUME OF FLOW: The quantity of fluid that passes a certain point in a unit of time. The volume of flow is usually expressed in gallons per minute for liquids and in cubic feet per minute for gases.

VOLUTE: A gradually widening spiral. A section or component of a centrifugal pump where velocity head becomes pressure head.

WATER DRUM: A tank at the bottom of a boiler, sometimes called MUD DRUM that equalizes distribution of water to the generating tubes and collects loose scale and other solids in boiler water.

WATER JACKET: Internal passages and cavities cast into the cylinder block of engines and air compressors through which water is circulated around and adjacent to friction (heat) areas.

WATER TUBE BOILER: Boiler in which the water flows through the tubes where it is heated by the gases of combustion.

WATT: The unit of electrical power.

WATTMETER: An instrument for measuring electrical power in watts.

WINCH: A hoisting or pulling machine fitted with a horizontal single or double drum. A small drum is generally fitted on one or both ends of the shaft supporting the hoisting drum. These small drums are called gypsies, or winch heads. The hoisting drums either are fitted with a friction brake or are directly keyed to the shaft. They are in the form of a spool and carry the working wire rope. The driving power is usually electricity, but hand power is also used. A winch is used principally for handling, hoisting, and lowering cargo from a dock or lighter to the hold of a ship and vice versa.

WINDLASS: An apparatus in which horizontal or vertical drums or gypsies and wildcats are operated by means of a steam engine or motor for the purpose of handling heavy anchor chains, hawsers, and so forth.

WIPED BEARINGS: A bearing in which the babbitt has melted because of excess heat.

WORK: The transference of energy from one body or system to another.

WORK REQUEST: Request issued to naval shipyard, tender, or repair ship for repairs.

WORM, WORM SHAFT: A threaded shaft designed to engage the teeth of a wheel lying in the plane of the shaft axis. This type of gear is used for the transmission of heavy loads at low speeds.

WYE GATE: A fitting with two separately controlled hose fittings, designed to connect to an outlet.

YOKE: A frame or bar having its centre portion bored and keyed or otherwise constructed for attachment to the rudder stock. Steering effort from the steering gear is applied to each end of the yoke for the purpose of turning the rudder.

ZERK FITTING: A small fitting to which a grease gun can be applied to force lubricating grease into bearings or moving parts of machinery.

ZERO SETTING: The output of a device when its input is minimum.

ZINC: (1) A primary metal useful in a number of anticorrosion applications. (2) A metal block or form placed in seawater systems to counteract the effects of electrolysis.