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 ships bridge to the engine room, steering gearroom, 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 materials ability to withstand a tensile, orpulling, 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 manufac-tured 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 vapor 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 disks operating facecomes to rest to provide a seal against leakage of liquid, gas, or vapor.

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.