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Davit. A crane used to lower and raise lifeboats and sometimes anchors. The rotary, or most common type, consists of a vertical pillar, round in section, with the upper portion bent in a fair curve and having sufficient out-reach to clear the side of the ship plus clearance. Each lifeboat has two davits, one near its bow and one near its stern; and they both rotate, lifting the boat from its stowage position on the deck, and swinging it clear of the side. This type of davit is usually stepped in a socket attached to the side of the vessel or on the first deck below the boat deck near the side. At the boat deck level it is held in place by a keeper or bearing.

Davit Bearing. See Davit Keeper.

Davit, Cat. A davit used in raising an anchor from the surface of the water or from under the hawse pipe.

Davit Cleat. This cleat is used for fastening the end of the boat falls. It is generally seized or lashed to the davit.

Davit Fairleader. An eye fitting seized or lashed to the davit and used to lead the end of the boat falls from the fixed block to the cleat.

Davit, Fish. A davit used in pulling an anchor on board from under the cathead.

Davit Head. This term applies to the swelled part of the top of the davit to which the boat falls are attached. This attachment is usually done with an eye bolt but sometimes with a yoke and bolt.

Davit Keeper. A ring-shaped fitting whose function is to hold the davit in position and also to serve as a side bearing.

Davit, Mechanical. Mechanical davits are those that are forced outboard by a mechanism.

Davit Pivot Disc. A circular piece of hardened steel with one side flat and the other side having a convex conical surface. It is set in the bore of the davit socket to form a pivot bearing for the foot of the davit.

Davit Socket. The fitting into which the foot of the davit is set. When used with a keeper or bearing it is a small casting a few inches in height. It is not uncommon to combine both keeper and socket in one piece which requires a much higher casting with a broader base.

Davit Spreader. A spectacle-shaped fitting, fastened, to the davit head for the purpose of attaching the end of the guy rope leading to the deck and the end of the span rope between davits.

Dead Center, Dead Point. Those points during the stroke of a reciprocating engine at which the line of action of the connecting rod and the axis of the crank shaft lie in the same plane.

Dead Eye. A solid oblate or flat circular piece of hard wood having three holes for reeving a lanyard in setting up the standing rigging. Where this method of setting up is employed, the lower dead eye is attached to the chain plate, the upper one to the shroud or stay, the lanyard is then rove through the two dead eyes forming a three-fold purchase.

Dead Flat. The midship portion of a vessel throughout the length of which a constant shape of cross section is maintained.

Dead Light. A term applied to a port lid or cover. A metal shutter fitted to protect the glass in a fixed or port light,

Dead Load, Nautical. A term used meaning the weight of cargo and stores carried by a vessel. A load steadily applied, as the weight of merchandise stored in a warehouse. In computing stresses in any structure the weight of the structure itself, if not moving, is a dead load.

Dead Plate. A flange at the lower edge of the furnace front or a plate which supports the forward end of the grate in a boiler.

Dead rise. The angle which the straight portion of the bottom floor of the midship section makes with the base line. It is expressed by the number of inches rise above the base line in the half beam of the vessel.

Deadweight. The total weight of cargo, fuel, stores and water which a ship can carry when at her designed draft. The term is frequently used as descriptive of the vesselís size. It must not be confused with the volume or cubic capacity of stowage space. See also "Useful Load." Deadweight is usually expressed in long tons.

Deadweight, Cargo Factor. A constant which if multiplied by the registered tonnage will give as a result the approximate deadweight cargo which the vessel can carry.

Deadweight Efficiency. The ratio of the deadweight to the designed displacement.

Deadwood, After. Timbers built up between the keel and keelson in the vicinity of the stern post.

Deadwood, Fore or Stem. Reinforcing timbers placed back of the joint of the stem and keel.

Dead-works. All parts of a vessel extending above the load water line.

Deck. A deck in a ship corresponds to the floor in a building. It is the plating, planking, or reinforced concrete covering or any tier of beams above the inner bottom, forming a floor, either in the hull or superstructure of a ship.

Deck, After. A term applied to a deck aft of the midship portion of a vessel.

Deck, Anchor. A term applied to the top of a small forecastle that is principally used for storage of anchors or for supporting anchor handling devices.

Deck, Awning. A term applied to a deck fitted from bow to stern on a light superstructure. The space below it is completely closed in and may be used for passengers or for the stowage of small or light cargo.

Deck Beam. See Beam, Deck.

Deck Beam Clamp. See Clamp, Deck Beam.

Deck, Boat. A superstructure deck provided for the stowage of the life boats and also generally used for staterooms or quarters.

Deck Bolts. The bolts that are used in fastening planking to the deck beams.

Deck, Bridge. A term applied to the deck forming the top of a bridge house, or partial superstructure.

Deck, Bulkhead. The uppermost continuous deck to which all the main transverse watertight bulkheads are carried. This deck should be watertight in order to prevent any compartment that is open to the sea from flooding the one adjacent to it.

Deck, Calked. A term applied to a steel deck having the edges of such plating and bars as are necessary to secure watertightness calked. It is applied to a wood deck when the seams between the planking are filled with cotton or oakum and payed with marine glue. Where planking is laid over a steel deck it is advisable to calk the planking only because any leaks in the wood covering would be held by the steel deck causing the wood to rot.

Deck, Canvas Covered. To secure water tightness wood decks that are not calked and also wood decks within the quarters are often covered with canvas. After the canvas is laid it is given a coat of paint.

Deck Cargo. A term applied to a cargo carried on deck.

Deck Chair. An item of furniture still found on beaches and in parks, but originally designed for the use of passengers and for easy stowing on liners. Developed from the hammock, and consisting of canvas stretched on a collapsible wooden frame. Luxury liners eventually had cane-seated, mahogany chairs, which, however, could similarly be collapsed.

Deck Covering, Decking. Various compositions and materials have been used for covering decks. The light upper weather decks are commonly covered with canvas and then given a coat of paint. The heavy steel weather decks, when not planked over, are often covered with a composition which serves as a protection to the steel and makes a better surface for working. The decks in the living quarters are usually covered with linoleum or some composition with the object of protecting the steel and of providing a surface that is easily kept clean and sanitary. In addition to the above some of the compositions are insulating and fireproof as well as elastic and neat appearing.

Deck Dowels or Plugs. Cylindrical plugs used to cover the heads of the bolts fastening the deck planking.

Deck Drain. A fitting attached to the deck in washrooms, shower spaces, etc., to which the drain pipes are connected.

Deck Erection. A term applied to a forecastle, bridge poop or deck house erected on the upper deck.

Deck Fitting. A fitting attached to a deck where a pipe line penetrates and the water tightness of the deck is to be maintained..

Deck, Flush. A term applied to a deck having no poop, bridge or forecastle erection that extends from side to side of the vessel.

Deck, Forecastle. A term applied to a deck worked from the stem aft over a forecastle erection.

Deck, Freeboard. The deck to which the classification societies require the vesselís freeboard to be measured. Usually the upper strength deck.

Deck Girder. See Girder, Deck.

Deck, Harbor. A term applied to the side deck lying close to the water line in a turret deck vessel. It is formed by the reverse curve of the plating lying between the trunk and sides of the vessel.

Deck Heights. The vertical distance between the molded lines of two adjacent decks.

Deck Hook. See Hook, Deck.

Deck House. A term applied to a partial superstructure that does not extend from side to side of a vessel like a bridge, poop or forecastle.

Deck, Hurricane or Promenade. A term applied to an upper superstructure deck on passenger ships.

Deck Line. A line drawn through the intersection of the molded line of the deck beams and the molded line of the frames. Approximately the intersection of the lower surface of the deck stringer plate with the inner surface of the shell plating.

Deck, Lower. A term applied to lowest deck in two and three deck vessels, and in the next to lowest in vessels having for or more decks.

Deck Machinery. A term applied to capstans, windlasses, winches and miscellaneous machinery located on the decks of a ship.

Deck, Main. A term applied to the principal deck. It is usually the one next below a complete top or upper deck.

Deck, Orlop. A term applied to the lowest deck in a ship having four or more decks.

Deck Paint. See Paint.

Deck Pillar. See Pillar, Decks.

Deck Planks or Planking. A term applied to the wood sheathing or covering on a deck. Oregon, yellow pine or teak are used for this purpose. The seams between the planking should be thoroughly caulked.

Deck Plates. Watertight hand or manhole plates usually let in flush with the deck for access to coal bunkers, operating rods, etc.

Deck Plate, Sounding Tube. A fitting attached to a deck and forming the terminal for a sounding tube. A screw plug is provided and is removed when sounding the inner bottom tanks.

Deck, Platform. A term applied to a partial deck fitted in the hold of a ship.

Deck Plating. A term applied to the steel plating covering a deck.

Deck Plug. A wood plug set in over the head of a deck bolt and cut flush with the surface of the planking.

Deck, Poop. A term applied to a deck worked from the stern forward over a poop erection.

Deck, Promenade. An upper superstructure deck on a passenger ship designed as a promenade for the passengers.

Deck, Quarter. A term applied to the after portion of a weather deck. In a warship that portion allotted to the use of the officers.

Deck, Raised Quarter. Term applied to the after portion of a weather or upper deck that is raised a few feet above the forward portion.

Deck Scuppers, Upper. Scuppers for draining water from the upper deck, gutters or waterways.

Deck, Shade. A very light deck fitted from bow to stern to provide protection against the weather. The sides below this deck are fitted with openings.

Deck, Shelter. A deck similar to an awning deck, but built on a very light superstructure.

Deck, Spar. A term applied to a deck fitted from bow to stern on a superstructure having heavier scantlings than those under an awning deck.

Deck, Steel. A deck constructed of steel plating on steel deck beams.

Deck Stringer. See Stringer, Deck.

Deck Stringer Bar. See Stringer, Bar.

Deck, Tongue and Groove. A deck covered with thin machined planks and generally used on the upper light decks of vessels. Tongue and groove decks are usually covered with canvas after which a coat of paint is applied.

Deck, Tonnage. The tonnage deck in vessels having three or more decks to the hull is the second deck from the keel, and in all other cases it is the upper deck of the hull. If the second deck from the keel consists of several partial decks extending with breaks from stem to stern, the line of that course of decks must be taken as the tonnage deck; and if the partial decks are at different heights, the line of the lowest will be taken as the tonnage deck and the head room above such line under the higher will be measured.

Deck, Trunk. A term applied to the top of a fore and aft trunk erected on the upper deck.

Deck, Turret. A term applied to the top of a trunk formed by curving in the sides of a vessel to form a side deck close to the water line and then curving the side deck up to form the sides of the trunk. In this way the plating makes a reverse curve from the sides of the ship to the top of the trunk.

Deck, Turtle. A term applied to a weather deck that is rounded over so that it has a shape similar to the back of a turtle. It is used on ships of the whaleback type and on the forecastle decks of torpedo boats.

Deck, íTween. A term applicable to any deck below the upper deck. Also the space between decks.

Deck, Upper. Generally applied to the uppermost continuous weather deck. Where this is an awning, shade or shelter deck, these terms should apply and the deck next below may be called the main or upper deck.

Deck, Weather. A term applied to the upper, awning, shade or shelter deck or to the uppermost continuous deck exclusive of forecastle bridge and poop that is exposed to the weather.

Deck, Wood. A term applied where a deck is constructed of wood planking. Also applied to the wood sheathing of a steel deck. Teak, Oregon or yellow pine are most commonly used for wood decks.

Deep Floor. See Floor, Deep.

Deep Frame. See Frame, Deep.

Deep Tank. A tank extending from the bottom of a vessel or from the top of the inner bottom up to or higher than the lower deck. Deep tanks are commonly fitted either forward or abaft the machinery space in cargo vessels. They are fitted with hatches, so that they may be used for cargo when loaded as well as for ballast water when light.

Deep Water Line. The water line at which a vessel floats even carrying the maximum allowable load.

Delivery Valve. See Valve, Delivery.

Depth by Lloydís Rules. The depth at the middle of length from the top of keel to the top of beam at side of uppermost continuous deck, except in awning or shelter deck vessels, where it may be taken to the deck next below the awning or shelter deck, provided the height of ítween decks does not exceed 8 feet. When the height of ítween decks exceeds 8 feet the depth is to be taken from the top of keel to a point 8 feet below the awning or shelter deck.

Depth Molded. The vertical distance from top of beam of uppermost strength deck at side of vessel amidship to top of keel.

Depth Recorder. A device invented by Sir Wm. Thompson, consisting of a composition cylinder containing a piston upon which the water acts against a spring. The distance the spring is compressed is recorded by a marker on the piston stem. As the recorder is brought to the surface, the piston returns to its original position but the marker remains at the point to which it was pushed, thereby indicating the depth to which the recorder was lowered.

Depth, Register. The register depth should be taken from the underside of the tonnage deck plank, midship, to the ceiling in the hold, average thickness, at the side of the keelson, in a direction perpendicular to the keel, which may be done by a square placed upon the upper side of the keelson. If the vessel has a third deck, then the height from the top of the tonnage deck plank to the under side of the upper deck plank shall be accounted as the height under the spar deck.

Depth Thermometer. A thermometer housed in a strong brass cage with a sturdy base and uprights, used by deep-sea fishermen to discover the water temperature at various depths. It was believed that if the temperature of the water was right then the fish could more easily be caught. Also used on hydrographic ships in ocean surveys.

Derrick. An apparatus designed to hoist heavy weights. The general design of a derrick is similar to that of a post crane except that the boom is hinged at the heel which allows it to be set at any angle with the post. The post of a derrick usually rotates with the boom.

Derrick, on a Ship. A spar or a boom, one end of which is stepped in a pivot bearing on the lower portion of a vertical post erected on the deck of a ship or on a pedestal fitted to the deck at the foot of the vertical post. A hinged connection fitted to the pivot bearing allows the boom to be inclined at any angle with the post while the pivot permits it to be revolved. The derrick is fitted with ropes, guys and tackles and is used for transferring cargo from and into the hulls. Unlike most derricks on land the derrick post itself does not revolve.

Destroyer. A naval vessel of small displacement and maximum speed having a battery of light rapid-fire guns and heavy deck torpedo tubes. These vessels have a moderate steaming radius and are intended for the protection of capital ships and for convoy and scouting duty.

Destroyer Leader. A war vessel of the destroyer type but larger. Her greater size makes it possible to provide more comfort for the personnel, a slightly heavier battery, slightly more speed, and a considerably greater cruising radius than is possible in a destroyer.

Devils Claw. See Chain Stopper.

Diagonal Plate. A term applied to plates fitted diagonally across the deck beams to tie them together. Wood planking is fitted above them.

Diaper Plate. See Horseshoe Plate.

Diaphragm, Turbine. See Turbine Diaphragm.

Die. A tool, having several cutting edges, used for cutting threads. In drop forging work a template tool used to stamp out a piece of work in one operation.

Die Sinkers. Workmen who make the tools by means of which the drop forging machines stamp the articles from the heated material.

Dipping. The vertical oscillation of a ship resulting from rolling or pitching. A very low position of the vesselís center of gravity or marked changes of the vesselís form in the vicinity of the waterline or a combination of both tend to accentuate dipping.

Diptych Dial. A form of portable sun dial, hinged in two parts connected by a cord. The part acting as a lid was at right-angles to the base so that the cord, tightened, acted as the upright gnomon or style to cast the shadow. Chiefly produced at Augsburg, Germany, in the form of the Augsburg Dial and Nuremberg Diptych.

Direct Acting Pump. See Pump, Direct Acting.

Direct Current. An electric current which flows in one direction.

Direct Acting Pump. See Pump, Direct Acting. .

Disc Cutter. A large thin metal circular saw without teeth which revolves at extremely high speed and is used to cut pieces of metal.

Dish Heaters. A warming closet or oven heated by a steam coil for use in heating dishes to prevent the food being rapidly cooled by coming in contact with the dish.

Dished. A term applied to the end of a cylinder or drum when it is concave.

Dismantle. To remove the sails, ropes, blocks and other gear that would become damaged by exposure if left without care.

Displacement. The amount or quantity of water displaced by a floating vessel. It exactly equals the weight of the vessel itself with whatever is on board at the time at which the displacement is recorded. Displacement may be expressed either in cubic feet or tons; a cubic foot of sea water weighs 64 pounds and one of fresh water 62.5 pounds, consequently one ton is equal to 35 cubic feet of sea water of 35.9 cubic feet of fresh water. The designed displacement of a vessel is her displacement when floating at her designed draft. In merchant vessels this is generally taken with full cargo, fuel, stores and water on board. In the case of naval vessels it corresponds to the vessel complete with full supply of ammunition, and two-thirds full supply of fuel, stores and water.

Displacement Length Coefficient. See Coefficient, Displacement Length.

Displacement, Volume of. The volume of water displaced by a vessel. In the English system of units the volume of displacement is given in cubic feet and equals thirty-five times the displacement in salt water or thirty-six times the displacement in fresh water.

Distance Finder. A navigational instrument used for finding the distance of an object, and particularly the distance of another ship to keep vessels in station. It consisted of a small sighting telescope, with movable prism plate and a diagram base plate. The last was graduated in cables, and engraved with dividing lines that radiated outwards from a central point like sunís rays.

Distiller. A chamber in which steam vapor from an evaporator is condensed, forming fresh water for drinking and other purposes. It consists essentially of a chamber into which the steam vapor enters and is condensed by a pipe coil through which cold sea water circulates.

Distiller Foundation. A term applied to the seating supporting a distiller.

Distiller Pump. See Pump, Distiller.

Distortion. Deformation from the natural or original shape of an object.

Ditty Box. A small box fitted with a hinged lid and lock, used by the crew on war vessels to hold thread, needles, combs, brushes, etc. Possibly from the Saxon "dite", meaning neat or tidy. Its forerunner, however, may have been a bag made of "dittis", which was a form of Manchester cotton fabric. Ditty bags are mentioned in naval records of at least two centuries ago.

Dividers. A two-pronged hinged instrument or "pair of compasses", for measuring on scales or marking off distances on a chart, introduced about 1703, made of brass usually in early versions, but later of other metals with steel points.

Dock. A basin for the reception of vessels. Wet docks are utilized for the loading and unloading of ships. Dry docks are utilized for the construction or repair of ships.

Docking Draft, Critical. See Critical Docking Draft.

Docking Keel. See Keel, Docking.

Docking Plug. See Bleeders.

Dockyard. A yard or plant where ships are constructed or repaired.

Dog. A short metal rod or bar fashioned to form a clamp or clip and used for holding watertight doors, manholes, or pieces of work in place. On watertight doors, it is usually a U shaped fitting composed of two main pieces, one of which is bent to form a right angle, having a handle on one end, the other end being passed through a gland in the door and having a screw thread cut on the end to which the second piece in the shape of a handle is attached. The complete dog provides a handle on each side of the door which when turned works over a wedge on the door frame and compresses a rubber gasket fitted to the door against the toe of the flange of the door frame. On manhole and hatch covers giving access to compartments in the shipís structure, the dogs usually consist of drop forged fittings riveted to the cover. U shaped openings in the dogs project over the edge of the cover a sufficient distance to allow drop bolts hinged to the manhole or hatch frame to be swung up into the openings and tightened by nuts. On manholes in boilers and tanks the dog consists of a strong back fashioned to the shape of an arc of a circle and spanning the manhole. A stay bolt passing through the manhole door and through a boss in the center of the dog allows the door to be tightened. On the floor where the shipís framing is curved to shape, the dog consists of a piece of steel rod bent to somewhat less than a right angle. One leg of the dog is put through a hole in the bending floor and the other end on the frame or piece of work to be bent. A few blows of the hammer near the apex of the angle of the dog is sufficient to clamp the work to the floor. For holding blocking together, the dog consists of a rod or bar of iron having its ends bent at right angles and pointed. In use the pointed ends are driven into the blocks to be held.

Dog, Shore or Dagger. A brace placed in such a position that it holds the sliding ways from slipping until all the necessary shores and keel blocks are removed, when it is itself removed allowing the ship to slide down the ways.

Dolly Bar. A steel bar used to hold the heads of rivet while the points are being clinched. A dolly bar is used where the space is not sufficient to use a holding on hammer conveniently.

Dolphin. A term applied to several piles that are bound together, situated either at the corner of a pier or out in the stream and used for docking and warping vessels. Also applied to single piles and bollards on piers that are used for docking and warping.

Donkey Boiler. See Boiler, Donkey.

Donkey Pump. See Pump Donkey.

Door. A swinging, sliding or removable part providing entrance or access to staterooms or compartments.

Door, Boiler Ash Pit. See Boiler Door, Ash Pit.

Door, Boiler Furnace. See Boiler Door, Furnace.

Door, Cargo. A door, usually composed of two or more parts, fitted in the side or an upper bulkhead of a vessel for the purpose of providing access through which cargo may be trucked.

Door, Dutch. A term applied to a door built in two independent sections, one above the other, so that the upper half may be open while the lower half is closed. These doors are commonly used for access to galleys.

Door Frame. A frame enclosing a doorway. It is generally composed of a horizontal piece at the top called a header, a horizontal piece at the bottom called a sill, the vertical sides called stiles and a piece which extends around the inside of the frame for the door to close against called the stop bead.

Door Gangway. A door fitted in the side of a vessel to provide access for a gangway.

Door, Horizontal or Vertical, Sliding. A door so constructed and operated that it can be slid, horizontally into position in the case of horizontal doors and vertically into position in the case of vertical doors. Such doors are usually watertight and so fitted with shafting and bevel gears or other means that they can be closed from the weather or upper deck.

Door, Joiner. A light door fitted for access to staterooms and quarters where watertightness is not required. These doors are made of wood, light metal plating and also of light metal plating on wood frames.

Door, Metallic. A term applied to a hollow metal joiner door. They are fitted in the living quarters aboard ship.

Door, Non-Watertight. A term applied to a door that is not constructed to prevent water under pressure from passing through.

Door, Screen. A wooden door frame over which single or double wire mesh is stretched.

Door, Slat or Blind. A door composed of a frame fitted with slats or blinds. They are fitted in conjunction with joiner doors to state rooms and also independently to some compartments.

Door, Watertight. A door so constructed that when closed it will prevent water under pressure from passing through. A common type consists of a steel plate, around the edges of which a frame of angle bar is fitted, having a strip of rubber attached to the flange that is parallel to the door plate. The strip of rubber is compressed against the toe of the flange of an angle iron door frame by dogs or clamps.

Door, Weather tight. A term applied to outside doors on the upper decks which are designed to keep out the rain and spray.

Double Acting Pump. See Pump, Double Acting.

Double Bottom. A term applied to the space between the inner and outer skins of a vessel. Also applied to indicate that a ship has a complete inner or extra envelope of watertight plating. A double bottom is usually fitted in large ships extending from bilge to bilge and nearly the whole length fore and aft.

Double Bottom Cellular. A term applied where the double bottom is divided into numerous rectangular compartments by the floors and longitudinals.

Double Bottom Plating. See Plating, Double Bottom.

Double Ported Slide Valve. A type of slide valve in which the ports are so arranged that for a given movement of valve twice the area of steam port is uncovered as would be the case in a simple slide valve of ordinary type.

Double Riveting. See Riveting, Double.

Double Whip. A rope rove through two single blocks, having the standing part made fast to a fixed object near the upper block or to the block itself.

Doubling Plate. See Plate, Doubling.

Doubling Shell. See Shell, Doubling.

Doubling Strake. See Strake, Doubling.

Douse. To cover suddenly with a liquid; to lower quickly as a sail; to extinguish suddenly.

Dowel, Butt. A cylindrical pin used in making end joints in timbers. A hole of the same diameter as the dowel is bored in the end of each timber and the pin is inserted in one timber and then the joint made by forcing it into the other.

Dowels, Joint. Rectangular blocks inserted in grooves cut in the sides of a pair of frames or timbers for the purpose of making them work together.

Downtown Pump. See Pump, Downtown.

Draft, Draught (of a vessel). The depth of a vessel below the waterline measured vertically to the lowest part of the hull, propellers or other reference points.

Draft Marks. The numbers which are placed at the bow and stern of a vessel to indicate how much water she draws. These numbers should be as near the stem and stern as possible and should be six inches high and spaced twelve inches apart vertically.

Draft, Mean. The mean of the drafts measured at the bow and the stern, or in the case of vessels with straight keels the draft measured at the middle of the waterline length.

Draftsmen. Men engaged in the preparation of the general and detail plans from which are built the shipís hull, machinery, fitting, etc.

Drag. See Anchor, Sea.

Drag. The designed excess in draft aft over that forward.

Drain Hole Plug. See Bleeder.

Drainage System. Piping located in the hold of a vessel and connected to drainage pumps for pumping overboard accumulations of water in the various compartments, hold, inner bottoms, etc.

Drawing Room Equipment. The equipment necessary to a drafting room to permit the engineers and draftsmen to carry on work such as making calculations, pencil drawings, tracings, blueprints, etc., for designs undertaken. It consists of drawing tables and benches, slide rules, calculating machines, plan filing cabinets, drawing instruments, scales, triangles, curves, splines, blueprinting and Photostat machines and miscellaneous supplies such as drawing paper, tracing cloth, blueprint paper, pencil ink, erasers, etc.

Dredge or Dredger. A vessel usually having a scow-shaped hull and equipped with especial machinery for use in deepening the channels of rivers, harbors, etc.

Dredging Pump. See Pump Dredging.

Dresser, Galley. See Galley, Dresser.

Drift. In erecting the structure of a ship it is often found that the rivet holes in the pieces to be connected are not concentric and the distance that they are out of line is called the drift. Where the drift is slight it can be corrected by reaming, but in many cases it is necessary to drive tapered pins far enough through the holes to bring them in line.

Drift Angle. The ample formed by the tangent to the vesselís path in turning and the fore-and-aft centerline of the vessel. Inasmuch as a shipís bow in turning tends to swing in toward the center of her turning circle, the propelling force delivered is along a line oblique to that of the vesselís motion. This is one of the reasons for a shipís loss of speed during the act of turning.

Drift Pin. A conical shaped pin gradually tapered from blunt point to a diameter a little larger than the rivet holes in which it is to be used. The point is inserted in rivet holes that are not fair, and the other end is hammered until the holes are forced into line.

Drill. A cylindrical shaped tool with cutting facets on one end.

Drill Drift. A wrench for releasing a drill from its socket.

Drill Frame Hoist. A machine designed for operating the drill frames used in submarine drilling.

Drill Press. See Drilling Machine.

Drill, Sensitive. A machine for drilling small holes, When small drills are used in a machine any undue pressure in feeding the drill will cause it to break. For this reason the pressure necessary for feeding must be plainly perceptible at the hand lever or other feeding device and sensitiveness in this respect is attained by making the parts light and easy to move or operate.

Drilling Machine. A machine designed for the purpose of drilling holes in metal, wood, fiber, etc.

Drilling Machine, Electric. A portable drilling machine driven by an electric motor and used for the same purpose as a pneumatic drilling machine.

Drilling Machine, Heavy Duty. A drilling machine especially adapted to rapid drilling. This type of machine was developed to drive high speed drills to the limit of their capacity.

Drilling Machine, Multiple Spindle. A drilling machine which is built in both vertical and horizontal designs, with which a number of holes may be drilled simultaneously. Some drilling machines equipped with multiple spindles are known as gang drills.

Drilling Machine, Pneumatic. Pneumatic drilling machines, or air drills, or pneumatic drills, as commonly called, are usually portable drilling machines driven by an air motor of the reciprocating piston type, which is contained within the casing of the machine. They are not only used for drilling, but for reaming, tapping, grinding, wood boring and countersinking.

Drilling Machine, Radial. A drilling machine with a vertical spindle which is carried by an arm that may be swiveled about a vertical column. The distinguishing feature of this machine is the radial adjust of the arm about the column, which adjustment, in conjunction with the traversing motion of the drill spindle head along the arm, makes it possible readily to locate the drill in any position within the range of the machine.

Drilling Machine, Upright. The most common form of drilling machine. The general design of the machine is vertical and the drill spindle is in a vertical position.

Drive, Electric. See Electric Drive.

Drop Forgers. Workmen who operate Iron forging machines.

Drop Forging Machine. See Forging Machine, Drop.

Drop Strake. See Strake, Drop.

Drum, Wildcat. See Wildcat.

Dry Compass. See Compass, Dry.

Dry Compass Card. The card showing the compass positions, and used in the dry compass as above. Early examples were drawn by hand. By the late 17th century they were engraved and printed, the north often being indicated by a nautical or state symbol. These cards, from the 13th to the 16th century, were mounted in lidded wooden bowls, but from the 16th century they were placed in brass bowls on gimbals, the last-named to stop the shipís movement from affecting the instrument. The area of the needle or lozenge was enlarged to increase the sensitivity of the card, but this added weight and caused wear of the pin; it could be blunted and thus affect the cardís rotation. So pins with hardened, ruby tips and caps of agate were introduced. In the 18th century the card was fixed with glue to a disc of mica to avoid distortion, but Thomsonís card was much better and lighter in the 19th century when it was printed on Japan paper. Strong silk threads formed a framework, from a stone cap and brass ring, to hold aluminum wires on which the silk paper card was glued, with the bar magnets below it.

Dry Dock, Floating. A hollow floating structure of L or U shaped cross section, so designed that it may be submerged, that a vessel may be floated into it, and that it may then raise the vessel and itself so that the deck of the dock and consequently the bottom of the vessel is above the level of the water. The bottom of a floating dry dock consists of one or more pontoons or rectangular shaped vessels with high wing structures erected on one or both sides according to whether the section is to be L or U shaped. The deck of the pontoon is fitted with stationary keel blocks and movable bilge blocks which can be pulled under a vessel from the top of the wing structure. Pumps are fitted in the wings by which the dock can be quickly submerged or raised. Floating dry docks are used for repairing and painting the under water portions of vessels and for docking a damaged vessel. They are usually made up of several pontoons connected by more or less flexible joints and by the continuous wing structure. A pontoon may be detached at any time and docked on the remaining pontoons, thus making the dock self-repairing. On account of the unequal distribution of weight, fore and aft, in a ship, the pontoons in way of the middle portion of the ship should be given more buoyancy or lifting power than the end pontoons by regulating the amount of water pumped out of each pontoon. If this is not done the stresses set up in the longitudinal members of the shipís structure are much larger than in an excavated dock. Floating dry docks recently designed, having truss girders in the wing structures should also reduce the stress in the docked ship to an amount well within the stresses allowed for in the vesselís design. Floating dry docks are much cheaper to construct than excavated docks, and they possess a further advantage in that they may be moved or towed to a desirable location.

Dry Dock, Graving. A basin excavated at a waterway and connected thereto by gates or a caisson which may be opened to let a vessel in or out and then closed and the water pumped out. The dock is fitted with stationary keel blocks and movable bilge blocks, which usually are fitted on rack tracks, allowing them to be pulled under a vessel before the water is pumped out. Graving docks are more common in Navy Yards, as they are more expensive to construct than floating docks. On the other hand, when once made, they are practically permanent and they supply a more rigid foundation for supporting a ship than the floating dock. The gate of a graving dock is usually a caisson or a complete vessel in itself, the cross section of which is generally elliptical in shape and having a strong rectangular shaped keel and end posts which bear against the bottom sill and side ledges at the entrance of the dry dock. The caisson is designed so that it may be submerged at the entrance of the dock until it rests against the sill, and it is also equipped with power and pumps so that it may raise itself. When a ship is to be docked, sluice valves in the caisson are opened until the water in the dock reaches the same level as the water outside. The valves are then closed and the caisson pumped out and swung to one side, allowing a vessel to enter the dock. The caisson is then swung back to close the entrance and submerged, completely separating the basin from the waterway. After the vessel is lined up over the keel blocks the water is pumped out of the dry dock. Graving docks are constructed by making a large excavation, driving pile or building concrete foundations in the bottom and by constructing wood, concrete or stone retaining walls around the sides. The sides are usually built in the form of steps.

Dry Dock, Railway. A railway dock consists of tracks built on an incline on a strong foundation and extending from a sufficient distance in shore, to allow a vessel of the maximum size that it is built for to be docked, to a sufficient distance under water to allow the same vessel to enter the cradle. The cradle running on the tracks may be of wood or steel fitted with keel and bilge blocks and sufficiently weighted to keep it on the track when in the water. A hoisting engine with a winding drum or wild cat is fitted at the in shore end of the railway which operates the cradle by a cable or chain. These docks are less expensive than either the floating or graving docks, and are extensively used for docking ships of moderate size. The older types of marine railways had their cradles designed so that a vessel, in entering the dock, grounded on the forefoot and pivoted as the cradle came out of the water to a position in which the vesselís keel was approximately parallel to the tracks. A later and better design has been developed in which the cradle is designed so that the whole vessel grounds at the same time, and which allows a ship to be pulled up on the shore on an even or approximately horizontal keel. Railway docks are usually designed for hauling a vessel up the tracks bow first, but side-haul docks have also been built.

Drying Oven. See Oven, Drying.

Dub. To smooth down; as to dub a spar or timber with an adze.

Ductility. That property of a material which permits of its being drawn out into a thread or wire.

Dug-out. A term applied to a boat fashioned out of a log.

Dump Scow. A flat bottom craft used for transporting rubbish, etc. No machinery is installed for its propulsion.

Dumping Boards. A term applied to the planks fitted on the top of the inner bottom underneath the hatch openings. These planks take the wear of the cargo when loading and protect the inner bottom plating.

Dunnage. Loose wood or waste material placed in the hold of a vessel for the protection of the cargo from dampness. Also used as descriptive of a sailorís kit or personal belongings.

Duplex Pump. See Pump, Duplex.

Dutch Door. See Door, Dutch.

Dutchman. A piece of wood or steel fitted into an opening to cover up poor joints or the crevices caused by poor workmanship.

Dutchmanís Log. A variation of the use of a log to ascertain the speed of a ship, being a piece of wood thrown overboard at the bow, whose time was measured between two marks on the gunwale or between two seamen similarly positioned.

Dynamo. See Generator, Electric.


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