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Machine Beveling. The operation of bending the flanges of shapes to given inclinations by machinery.

Machine Screw. See Screw.

Machinery Arrangement. The term "machinery arrangement" applies to the layout of the main propelling unit and its auxiliaries.

Machinery, Auxiliary. See Auxiliary Machinery.

Machinery, Deck. See Deck Machinery.

Machinists (Inside). Mechanics who operate drills, lathes, boring mills, shapers, etc., in the shop. They prepare the parts of machinery for assembling.

Machinists (Outside). Mechanics who assemble on shipboard the propelling machinery and auxiliaries. On naval vessels they assemble the turret rotating machinery.

Macomb Strainer. See Strainer, Macomb.

Magazine. Spaces or compartments devoted to the stowing of ammunition.

Magnetic Field. The space surrounding a magnetized body through which the magnetic force acts.

Magnetism. The property possessed by certain bodies to attract and repel each other according to determinate laws.

Main Body. The hull exclusive of all deck erections, spars, stacks, etc.; the naked hull.

Main Check Valve. See Valve, Main Check.

Main Circulating Pump. See Pump, Main Circulating.

Main Deck. Deck, Main.

Main Deck Sheer strake. The strake or outside plating adjacent to the main deck.

Main Deck Stringer. See Stringer, Main deck.

Main Deck Stringer Bar. See Stringer, Bar.

Main Drain. The principle drainage main usually applied only to the pipes arranged for pumping out the machinery spaces.

Main Feed Pump. See Pump, Main feed.

Main Floor. See Floor, Main.

Main Frame. See Frame, Main.

Main Hatch. See Hatch, Main.

Main Hold. The largest cargo hold.

Main Piece, Rudder. See Rudder, Main Piece.

Main Truck. See Truck.

Mainsail. The principal sail carried by the main mast. In a square rigged vessel it is suspended from the main yard. In a fore-and-aft rigged vessel it is spread on the main gaff and boom.

Male and Female. A term applied to two engaging pieces, one of which is raised and the other recessed.

Malleability. That quality of a material by virtue of which it may be satisfactorily worked under the hammer or by means of rolls.

Maneuvering Valve. See Valve, Maneuvering.

Manger Plate. A term applied to a plate forming part of a breakwater. They are installed on forward weather decks for the purpose of throwing off the water that is shipped over the bow.

Mangle Rolls. See Rolls, Mangle.

Man of War. A vessel designed for fighting purposes. Generally applied to naval vessels of the first class.

Manhole. A round or oval hole cut in floors, tank tops, decks, tanks, boilers, etc., for the purpose of providing access.

Manhole Coaming. See Coaming, Manhole.

Manhole Cover. A cover or lid used to close a manhole opening. Manhole covers may be air, water, steam or oil tight. The simplest type consists of a plate and gasket fastened by bolts but for easy access and tightness a hinged cover on a raised frame is more desirable.

Manhole Ring, Boiler. See Boiler Manhole Ring.

Manholes, Boiler. See Boiler Manholes. .

Manifold. A casting or chest containing several valves. Suction or discharge pipes from or to the various compartments, tanks and pumps are lead to it, making it possible for several pumps to drain from or deliver to a given place through one pipe line.

Manila. The prepared fiber obtained from the stalk of the wild banana. The principal supply comes from the Philippine Archipelago. It is light and flexible, and does not readily deteriorate, so that when made into cordage it does not require tarring.

Manila Rope. See Rope, Manila.

Margin Bracket. See Fame Bracket.

Margin Line. A line drawn parallel to the bulkhead deck at side lines and 76 millimeters (equivalent to 3 inches) below the upper surface of that deck. The term is used in connection with the method of subdividing merchant ships described in the Report of the Committee appointed by the president of the British Board of Trade.

Margin Plank. A term applied to the plank forming the boundary of the deck planking.

Margin Plate. The plate forming the side of the inner bottom tank. This plate is usually fitted normal to the shell to which it is attached by a continuous angle bar and has its top edge flanged over to make a seam. The side frames are usually attached to this plate by large brackets.

Marine Compass. See Compass.

Marine Engine. See Engine, Marine

Marine Glue. See Glue, Marine.

Marine Hardware. A general term usually applied to spikes, nails, screws, clinch rings, boat hooks, row locks, pipe fittings, hinges, locks, door knobs, draw pulls, etc.

Marine Railway. See Dry Dock, Railway.

Marine Railway Hoist. See Hoist, Marine Railway.

Marker. A short piece of brass pipe which is dipped in white lead and pushed through a mold to mark the location of a rivet hole on the material.

Marker, Double Arm. A device consisting of two wooden arms or battens rigidly fastened together at one end in such a manner that they are parallel. Both arms are drilled with holes directly opposite each other. This device is used when it becomes necessary to transfer the location of a rivet hole from one side of a plate or shape to the other.

Marline. A double threaded, left handed tarred cord, made from a good grade of American hemp. In general use on shipboard for purposes similar to other small stuff.

Marline. A tarred hemp, two-stranded, left-handed, small stuff, about 1/8 inch in diameter, used for neat seizings and fine service. Untarred marline is used for making sennit.

Marline Hitch. A half hitch in which the hauling part comes out underneath the standing part. Used by riggers in marling down parceling before serving and for lashing hammocks.

Marline Spike. A tapering pointed metal implement used by riggers and sailmakers to open the strands of rope in splicing and as a lever in marling and seizing. In general, a marline spike is the same as a fid except that the former is metal while the latter is wood, although a marline spike may have a wood handle.

Marling. To hitch marline, spun-yarn, etc., around the parceling on a rope to keep it in place while the serving is being done.

Marry. To join two ropes end to end in such a manner that the joint will run through a block; also to place two ropes alongside of each other so that both may be hauled on simultaneously.

Martingale or Martingale Boom. A spar erected perpendicular to the forward end of the bowsprit as a strut for the jib-boom and flying jib-boom stays.

Martingale Guys. Stays running from the martingale to each side of the bow.

Martingale Stay. See Jib-Boom Stay.

Mast. A long pole of steel or wood, usually circular in section, one or more of which are erected vertically on the center line of a ship. The mast may be in one piece or it may be a series of pieces banded together to form one continuous pole. The masts were originally erected for the sails but they are now used more as supports for the rigging, cargo handling gear and wireless.

Mast Cap. A band worked around two sections of a mast at the level of the top of the lower section and serving as a support for the upper section. Also applied to the band around a topmast to which the stays are attached.

Mast Cheeks. A term applied to brackets of metal or wood fitted over on each side of a mast underneath the crosstrees or a mast platform.

Mast-Coat. A canvas covering fitted around and lashed or nailed to a wood mast just above the upper end of the mast wedge and also secured at the deck to prevent leakage around the mast.

Mast Collar. A piece of wood or a shape, usually an angle iron, that is formed into a ring and fitted around the mast hole in a deck.

Mast Fittings. Bands, caps, pads, etc., fitted to a mast of supporting topmasts, heels of booms, etc., and to which the shrouds, blocks, etc., are secured.

Mast, Fore. The mast that is farthest forward in all vessels having two or more masts.

Mast, Heel of. A term applied to the lowest portion of a mast.

Mast Holes. A term applied to the holes in a deck through which the mast passes.

Mast Hounds. The upper portion of a mast at which the outrigger or trestle trees are fitted. Also applied in vessels without outriggers to that portion at which the hound band for attaching the shrouds is fitted.

Mast, Jury. A term applied to any mast temporarily erected to take the place of one that is carried away. Also applied to a temporary mast erected in a new vessel.

Mast Ladder. See Ladder, Mast.

Mast, Lower. A term applied to the lowest part of a mast made up of two or more poles.

Mast, Main. The principal mast in a vessel. It is generally the second mast from the bow.

Mast, Mizzen. A term applied to the third mast in a vessel.

Mast Partner. A term applied to wood planking or steel plating worked around the mast hole in a deck to form a side support for a mast.

Mast Rope. See Rope, Mast.

Mast, Royal Topgallant. The third section above the lower mast. Its use is confined to square riggers.

Mast Step. A term applied to the foundation on which a mast is erected.

Mast Table. A structure built up around a mast as a support for the cargo boom pivots.

Mast, Top. A term applied to the portion next above the lower mast in a mast made up of two or more poles. Where the mast consists of two poles it is the upper pole.

Mast, Topgallant. That topmost portion of a mast made up of three poles. The pole next above the topmast.

Mast Trunk. A term applied to a well constructed in a vessel into which a mast may be lowered.

Mast Wedges. A term applied to the wood wedges driven around a mast where it pierces the deck in order to hold it in place.

Masthead. The upper portion of a mast above the hounds.

Mathematical Lines. Lines of a ship the offsets of which have been developed by mathematical means, i. e., by the use of formulae, coefficients, etc., rather than by the eye at the dictation only of judgment and experience.

Mathematical Wave. A wave whose contour follows some definite mathematical law. The best known mathematical wave is the Trochoidal wave.

Matthew Walker Knot. See Knot, Matthew Walker.

Mean Effective Pressure. The total area of the indicator card divided by the length of stroke.

Mean Sinkage. The change in a vessel’s mean draft which occurs as the result of an increase in her displacement.

Measurement. The ascertaining of the tonnage of a part or the whole of a vessel either from the plans or from measurements made on the ship according to certain definite rules.

Measurement, New. The measurement of tonnage according to the revised ruling which established l00 cubic feet as the space equivalent of one ton of cargo.

Mechanical Davit. See Davit, Mechanical.

Mechanical Ventilation. See Ventilation, Mechanical.

Mechanical Work. The product of a force by the distance through which it operates. In the English system of measurements the unit of mechanical work is the foot pound. It is equal to the work required to raise a mass of one pound a distance of one foot against the action of the force of gravity.

Messenger Chain. A term applied to a chain used in transmitting motion from one machine to another. A chain used in driving a windlass from a winch.

Messenger Wheels. A term applied to wheels that are fitted to two machines for the purpose of allowing one machine to drive the other by means of a messenger chain or rope. They are more commonly used in driving a windlass from a winch.

Metacenter, Longitudinal. The metacenter corresponding to longitudinal inclination.

Metacenter, Transverse. The point of intersection of the vertical through the center of buoyancy of a ship in the equilibrium with the vertical through the new center of buoyancy when the ship is slightly heeled. The displacement is the same in both the inclined and vertical positions referred to.

Metacentric Diagram. A curve indicating the height of metacenter (generally above base) for all drafts to which the vessel may be loaded.

Metacentric Height. The distance between the center of gravity and the metacenter. It is termed transverse or longitudinal as the transverse or longitudinal metacenter is used.

Metacentric Involute. The locus of the centers of curvature of that curve which is described by the center of buoyancy of a vessel as she is continuously inclined from the upright through all angles of heel.

Metacentric Stability. Initial stability, stability at small angles, which is correctly indicated by the metacentric height.

Metals. Common metals utilized in shipbuilding are as follows:


Admiralty Metal is a brass to which at least 1 per cent of tin has been added. It is light yellow in color. It cannot be worked hot except within narrow limits of temperature and for that reason is generally drawn cold from the casting form to the finished product. It resists the corrosive action of sea water. The main use of admiralty metal is in the manufacture of condenser tubes.

Commercial Brass Castings contain from 20 per cent to 40 per cent zinc. The straight alloy of copper and zinc with the zinc content below 35 per cent is soft and ductile and drags severely under the tool. The addition of a small percentage of tin hardens it and the addition of lead improves the machining qualities, causing the chips to break. It is used for the manufacture of oil cups, name and number plates and castings where strength is not required.

Commercial Rolled Brass is used for the manufacture of brass sheets for liners, trim, etc., brass pipe hand rails, distributing oil tubes and water pipes, It is also used in the manufacture of brass rod where strength and incorrodibility are not required.

Muntz Metal is used in making castings and is rolled into bars, shapes and plates. It is employed in the manufacture of bolts and nuts; it is rolled into plates and used for sheathing ship’s bottoms and drawn into tubes for condensers, oil coolers, etc.

Naval Brass Castings are employed for making hatch-frames, hatch-cover frames, door frames, scuttle-frames, fittings for mess tables and benches, skylights and chest hinges and fittings; rail and ladder stanchions, brackets, clips, fittings for canopy frames, brass valves and fittings of ventilation systems (except working parts), belaying pins, tarpaulin hooks, brass-pipe flanges, valve hand-wheels, handrail fittings, ornamental and miscellaneous castings and valves in water chests of condensers, etc., aboard ship.

Rolled Naval Brass resists corrosion by salt water. It is employed in the manufacture of bolts, studs, nuts, turnbuckles, rolled rounds, pump rods, tube sheets, supporting plates, shafts for valves in water heads and especially for propeller-blade bolts, air pump and condenser bolts and parts requiring strength and incorrodibility. If properly heat treated, the material is suitable for use in automatic or screw machines. It is supplied in rods, shapes, plates and tubing.

Brazing Metal

Brazing Metal is used in the manufacture of flanges for copper pipe and other fittings that are to be brazed. This is not to be confused with Brazing Spelter which has a chemical analysis of about 50 per cent zinc and 50 per cent copper, or a brass which is often employed for brazing brass, copper, iron or steel and has a composition of about 80 per cent copper and 20 per cent zinc.


The bronzes are alloys consisting mainly of copper and tin. It is to be regretted that manufacturers often employ the terms Bronze and Brass indiscriminately. The terms brass (which consists mainly of copper and zinc) and bronze (which consists mainly of copper and tin) should be used in accordance with their firmly established English language meanings.

Aluminum Bronze is employed in the manufacture of castings such as struts, rudder frames, propeller blades, worm wheels, gears, etc., in fact, in all casings that require strength and must resist corrosion. in the manufacture of aluminum bronze. Rolled aluminum bronze may be used for valve stems, propeller-blade bolts, air pump and condenser bolts, etc., and for all purposes requiring great strength. It possesses good bearing qualities and resists corrosion

Gun Metal is a bronze that was used for the manufacture of ordnance before steel became available. It is now employed extensively in valve bodies, gear wheels, bronze sleeves for propeller shafts, large bearings, pump manifolds, bolts and nuts, and in fact all miscellaneous composition castings where strength is required. Gun metal cannot be worked hot except within such narrow limits of temperature as to render the process impractical.

Journal Bronze is often specified for use in moving parts subject to considerable wear. It is harder than Gun Metal and is generally used in the smaller bearings. It is also employed for bushings, slippers, guide gibs and in reciprocating engines in valve crosshead bottom brasses, link block gibs and suspension link brasses.

Manganese Bronze (Cast) is used primarily in the manufacture of propeller blades, and propeller hubs.

Manganese Bronze (Rolled) is used in the manufacture of rolled round rods requiring great strength, where subject to the corrosion of salt water, valve stems, propeller-blade bolts, air pump and condenser bolts, etc.

Phosphor Bronze (Cast) is used in the manufacture of fittings that are exposed to the action of salt water; gears, driving and main nuts of steering gears and parts where strength, good bearing qualities and incorrodibility are requisites.

Valve Bronze is used extensively in the manufacture of all sizes of low pressure valve bodies and high pressure valve bodies under 4 inches in diameter. It is easier to produce sound castings with this mixture than with Gun Metal. This is probably due to the higher zinc content. Mechanical properties of Valve Bronze are usually not specified when ordering inasmuch as Gun Metal is used where great strength is required. It is suitable for use in the manufacture of castings subjected to severe stresses and the corroding action of salt water.


The metal has a light reddish color and is so brittle that it can readily be pulverized. It is used only in alloys, usually for the purpose of obtaining a low melting point although it has a hardening effect on lead. "Wood’s Metal" 50 per cent bismuth, 25 per cent lead, l2.5 per cent tin, and l2.5 per cent cadmium, with a melting point of 149° F. is the best known of the Bismuth alloys. Other alloys can be produced to obtain any desired fusing point. Such alloys may be used in connection with electric wire alarms, opening a circuit when melting, or for allowing automatic fire sprinklers to open at the proper temperature.


A lustrous bluish-white metal. Its melting point is 500° F., specific gravity 8.6 to 8.7 and boiling point 680° F. It is used in combination with lead, tin, and bismuth to form alloys when a low fusing point is desired.


A metal readily distinguished by its peculiar reddish color. It is very ductile and malleable and second to iron in tenacity and in commercial importance. On account of its high ductility, sheet copper can readily be worked while cold into complicated shapes by means of the hammer; hammering tends to harden the metal and finally cause it to crack but annealing at a low temperature restores the original ductility. Castings of pure copper are usually imperfect; 1 per cent of boron suboxide flux added to the molten copper gives a fair casting. Copper castings are rarely used except for purposes where high electrical conductivity is required. Copper resists the corrosive action of the elements although it is attacked by ammonia and to some extent by the more common acids.

Copper Alloys

Copper is the principal constituent of the various grades of brass and bronze and enters to a greater or less extent in the various alloys used for bearings. It is alloyed in varying proportions with gold and silver to increase the hardness of the resultant alloys. Uses: In addition to the use of copper in the alloys noted above, wrought copper is extensively used for electrical purposes on account of its high electrical conductivity, for tubes in feed water heaters and similar purposes where high heat conductivity is desired, and for pipes and sheathing where considerable ductility or resistance to the corrosive action of the elements is desired. The Alloys (brass and bronze) possess greater strength than copper alone, and are more easily machined, which renders them superior to copper for many purposes.

Cupro Nickel or Benedict Nickel

Cupro Nickel or Benedict Nickel is employed in the manufacture of tubes for condensers, distillers and feed-water heaters. The addition of a small percentage of manganese facilitates the proper working of the alloy in ingots and under rolls.


A metal of bluish-gray color and dull metallic luster. Its color turns to dull gray on exposure to air. It resists the action of most acids and the ordinary corrosive effects of air and moisture, but is readily attacked by alkalies. Has a tendency, increasing with an increase in temperature, to flow under slight pressure continuously applied and therefore must be rigidly supported to retain its shape.

Lead Alloys

Lead is alloyed with tin in various proportions to form common solder, "half and half" being a standard commercial brand suitable for general use. The alloying of lead with a small percentage of antimony, makes the hardness of the alloy considerably greater than that of the lead alone, without materially affecting the other properties. Lead is alloyed in various proportions with a number of other metals to form "bearing metals"; as it possesses valuable antifriction properties but is far too soft to be used alone. From 1 per cent to 10 per cent of lead is frequently added to brass or bronze, making the material easier to work with machine tools and less likely to leak under hydrostatic pressure; it has in all cases a tendency to weaken the alloy to which it is added although with less than 2 per cent of lead there is but slight weakening of the alloy and a material increase in ease of its machining. Uses: In alloys, as noted above; in the form of sheets and pipe, lead is extensively used for handling acids as protection against acid fumes. A lead sheathing is frequently used on insulated wires and cables as a protection against the action of moisture and acids. Lead pipe is convenient for use for ordinary plumbing purposes on account of ease in manipulation but on account of its mechanical weakness, it is inferior to iron pipe.


A silver white metal. It is malleable and ductile. It burns in air with intense white light. It is used in the form of ribbon or powder for flashlights and signals.


A silver-white metal. It is a liquid at ordinary temperature, but freezes at -39° F., and boils at 680° F. It is not affected by the atmosphere at ordinary temperatures but oxidizes when near its boiling point. It is tarnished by sulfur fumes and by dust, but may be cleaned by straining through cloth or chamois skin. It readily amalgamates with gold, tin, lead, zinc, and to a less extent copper and most of the other metals except iron and platinum, causing it to tarnish and lose its perfect fluidity. Glass containing a considerable amount of lead will affect mercury if left in contact with it for a long period.


A metal with a white luster, strongly resembling silver in appearance and not tarnishing under ordinary atmospheric conditions. It is attracted by a magnet, but less strongly than iron and can retain magnetism. It can be used in castings or rolled into sheets or rods.

Nickel Alloys

Nickel is a very important constituent of many alloys, in most cases having a tendency to impart ductility, strength and toughness to the alloy "Nickel Steel" and ’"Chrome-Nickel Steel" (See Steel) are of the greatest commercial importance. It is used in the manufacture of instruments of various kinds and as a "resistance metal" in electrical work. "Resistance Metals" include a number of alloys of nickel with copper, iron, chromium, or manganese. They are used for electrical purposes and are generally superior to German Silver for such use. "Nicrome" or "Nickel-Chromium Alloy" is used principally on the resistance element of electrical heating apparatus; it possesses high resistance and will stand long and repeated heating to a white heat without oxidation or other changes in its characteristics. Uses: In addition to its use in alloys, and for nickel plating, by the electrolitic process; pure nickel is used to a considerable extent where ability to stand high temperature and corrosion, combined with great strength is desired. Among these uses are valve stems, seats, and discs for use with high pressure superheated steam; and keys and bolts in locations where some other metals have failed.


A metal of bluish-white color that tarnishes and whitens slightly on exposure to the air. Zinc is but slightly attacked by the action of air and moisture but is attacked readily by acids or alkalies.

Zinc Alloys

Zinc is used principally for the manufacture of brass, bronze, and bearing metals; for which purpose it is alloyed with copper, tin or other metals. On account of its volatility there is always a loss of weight during the hot galvanizing process and in melting brass or bronze. Uses: Aside from its use in alloys, zinc is used principally for galvanizing iron or steel, as described under galvanizing. The practice of suspending slabs of zinc in steam boilers to prevent corrosion of the boiler through electrolitic action has been found to be of but little value.

Metal Furniture. Berths, cabinets, lockers, etc., made of light metal. They are often decorated and finished so that they resemble wood.

Metal Polishers. Men who put the required finish or polish on parts of machines, fittings, etc., by means of a power-operated wheel turned at high speed and known as a buffer.

Metal Specialties. Includes such items as the end strips for linoleum and matting, moldings, tubes, special shapes, etc.

Metallic Cabinet. See Cabinet.

Metallic Flooring. See Flooring, Metallic, and also Gratings.

Metallic Paint. See Paint.

Meter, Electric. A measuring instrument for determining the magnitude or relation of the quantities in an electric circuit

Microfarad. The practical unit of electrical capacity. It is the millionth part of the farad.

Middle Body. That portion of the ship adjacent to the midship section. When it has a uniform cross section throughout, its length its waterlines being parallel to the centerline, it is called the parallel middle body.

Middle Line. Sometimes used in lieu of centerline, particularly with reference to bulkheads, floors or other transverse members of the vessel.

Midship Deep Tank. A compartment located near the middle length of a vessel used for carrying liquid cargo, fuel or water ballast, and having bulkheads and flats for its sides and top, as distinguished from a double bottom tank having the inner bottom for its upper limit.

Midship Floor. See Floor, Midship.

Midship Frame. See Frame, Midship.

Midship Section. The vertical transverse section located at the mid-point between the forward and after perpendiculars. Usually this is the largest section of the ship in area.

Midship Section Coefficient. See Coefficient, Midship Section.

Midships. Same as Amidships.

Mild Steel. See Steel and Iron.

Mile, Nautical. See Nautical Mile.

Mill Men. Men who work in a saw mill operating wood working machines.

Milling Cutter. A tool usually of cylindrical form, but also shaped to meet requirements, having teeth or edges for cutting. Milling cutters are mounted on an arbor or have an integral shank for holding them in a machine.

Milling Machine. A machine in which the tool or cutter rotates and the work is fed automatically in the required direction. The cutter has a number of teeth or cutting edges which successively mill away the metal as the cutter rotates.

Milling Machine, Key Seating. A machine designed for milling keyways. Keyways located in shafts, etc., where the ends are not open, are generally milled.

Milling Machine, Universal. A milling machine, the work table and feeds of which are specially arranged for doing all classes of plane, circular, helical, index or other milling.

Milling Machine, Vertical. A milling machine designed with a vertical spindle for holding the cutter.

Miter Gear. A bevel gear wheel, the sides of which are beveled to an angle of 45°.

Mitered. The operation of making a joint between two timbers, that lie at right angles to each other, by cutting the ends of each to an angle of 45°.

Mold. To draw out to full size the lines of a vessel or part of its structure; a pattern or form built up to show the contour or shape of anything.

Mold, Beam. A pattern showing the curvature, commonly called camber, of the beams for a deck.

Mold Loft. A space used for laying down the lines of a vessel to actual size and making templates therefrom for the structural work entering into a hull. The second floor of a large building is usually used as a mold loft, the floor being cleared and planed true. A vessel’s lines are drawn in and faired on the floor, the body lines being scrived in to insure their being preserved until the structural work is completed. Practically all the templates for shaping and laying out the structural work in a ship are made in the mold loft from the lines on the floor. Upon the completion of the mold loft work on a vessel the floor is planed clean before laying down the next ship. On account of the desirability of having the mold loft as level as possible and to prevent warping it generally consists of two layers of planking laid diagonally and opposite. This method prevents the floor from warping, provides a top facing that may be renewed after being planed thin and on account of the seams running diagonally there is less likelihood of the lines laid down following a seam in the floor.

Mold, Skeleton. A template or pattern, made up of open framework instead of solid, to show the outline of some part.

Molded Breadth. The ship’s maximum breadth measured to the outside or heel of frame bar and occurring generally, though not always, at the midship section.

Molded Depth. The vertical distance from the base line to the molded line of main deck at side measured at the midship section.

Molding. Ornamental strip either of wood or metal used for finishing purposes.

Molding, Knuckle. A batten or strip of wood or steel usually cut to a half round cross-section and used to cover the knuckle line.

Molding Machine. A machine for making wood molding. The knives are usually attached to a cutter head carried on a horizontal spindle which is supported over the work table. Rolls and springs are provided for feeding the work to the machine and holding it in place during the operation.

Molding Machine, Variety. A wood working machine designed to cut moldings on the edges of the work. The cutting tools or knives for this type of machine are carried on a vertical spindle projecting through the work table and the work rests on the upper surface of the table and is fed to the cutters by hand.

Molding of a Floor. Its depth.

Molding of a Frame. The measurement of the athwartship flange or web of a frame.

Molding of a Keel. Its depth, or dimension perpendicular to the bottom line.

Molding of a Keelson. Its depth.

Molding of a Stem. Its depth or dimension fore and aft.

Molding of a Sternpost. Its depth or dimension fore and aft.

Moment. The moment of an elementary mass about a plane is the product of the mass times its algebraic distance from that plane. The algebraic distance is plus when on one side and minus when on the other side of the reference plane. The moment of a body about a plane is the algebraic sum of the moments of the elements of mass constituting that body. If the body is of infinitesimal thickness, the reference plane becomes a line, which line is termed the axis of moments. If now the mass of elementary thickness be assumed of uniform density throughout, the conditions for considering geometrical moments of plane areas are fulfilled. Geometrical moments of plane areas are measured in units of area times units of length, no account whatsoever being taken of mass. Likewise, the geometrical moment of a volume is measured in units of volume times linear units, the volume being considered of uniform density, but no definite value being assumed. The moment of any body or volume about a plane or of any area about an axis is numerically equal to the product of the mass of the body or of the volume or area times the algebraic distance of the reference plane (or line) from the center of gravity of the body (volume or area). The moment of a force about any point is the product of the force times the distance of its line of action from the point. The moment of a force is measured in units of weight times units of distance as foot tons or foot pounds.

Moment of Inertia. The moment of inertia of an elementary mass about a plane or an axis is the product of the elementary mass times the square of its distance from the reference plane or axis. The moment of inertia of a body about a plane or an axis is the sum of the moments of inertia of all its elements of mass about the reference plane or axis. The moment of inertia of a body about an axis is ordinarily termed its polar moment of inertia. If the body is of an indefinitely small and uniform thickness and is of uniform density, the conditions are fulfilled for considering the geometrical moment of inertia of a plane area. Under these conditions the reference plane becomes a line termed the axis, and in the case of the polar moment of inertia the axis becomes a point. Geometrical moments of inertia of plane areas are measured in units of area times linear units squared. In a similar manner geometrical moments of inertia of volumes are measured in units of volume times linear units squared. The moment of inertia of any body (volume or area) about a plane (or axis) is equal to the mass of the body (or volume or area) times the square of the distance between the reference plane (or axis) and a parallel plane (or axis) through the center of gravity of the body (volume or area) plus the moment of inertia of the body (volume or area) about the parallel plane (or axis) through its center of gravity.

Moment of Inertia of Section. The sum of the products formed by the multiplication of the mass of every particle of a material system by the square of its distance from a straight line known as the axis.

Moment to Alter Trim. The moment, i. e., the weight times the distance which it is moved which is required to effect a change in the trim of a vessel of one inch.

Monitors. A type of war vessel intended principally for work against shore batteries and fortifications. Its principal characteristics are moderate displacement, low speed, very low freeboard, heavy main battery guns, and good cruising radius. The modern type of heavy gun emplacement known as the turret was first used on vessels of this type.

Monkey Forecastle. A small forecastle. The enclosed space is generally used for the accommodation of anchor handling appliances and the deck proper for the stowage of the anchors themselves.

Monkey Tail. A term applied to a curved bar fitted to the upper, after end of a rudder and used as an attachment for the rudder pendants.

Monorail Hoist. A type of hoisting gear, usually electric, designed to travel along a single overhead track.

Mooring. A term applied to the operation of anchoring a vessel in a harbor, securing her to a mooring buoy or to a wharf or dock by means of chains or ropes.

Mooring. To make a vessel fast to a buoy, quay or wharf or by anchoring. Technically, a vessel is moored when she has two anchors down at a suitable distance apart with such a length of chain on each that she is held with her bow approximately stationary on a line between them, although allowing the stern of the vessel to swing with the tide and wind.

Mooring Anchor. See Anchor, Mooring.

Mooring Bitts or Bollards. See Bitts, Mooring.

Mooring Buoy. See Buoy, Mooring.

Mooring Machine. A term applied to a machine that is similar in construction to a winch and which is used for the purpose of docking and warping vessels. Automatic control of the tension in the mooring lines to take care of the change in trim, draft, and the tides are obtained in some makes of these machines.

Mooring Pipe. A round or oval casting or frame inserted in the apron plate or bulwark plating of a ship through which the mooring chains, hawsers or warps are passed.

Mooring Staple. A single or double ring shaped fitting attached to the shell of a ship for the purpose of securing mooring lines.

Mooring Swivel. A device generally used by men-of-war in mooring to prevent a foul hawse. The cables are disconnected and shackled to the swivel just forward of the stem. When the ship swings the swivel turns and the cable is kept clear. The swivel is similar to the usual form, but larger and heavier, and is fitted at either end with two links and shackles for attaching to the cables.

Moorings. Heavy chains permanently anchored in a harbor to which vessels may ride. To these are attached buoys having chains of the proper length and strength to haul the fast on board through the hawse pipes.

Mortising Machine. A wood working machine in which an auger and a chisel are worked automatically in performing the operations necessary to produce the square or rectangular mortise usually employed in wood work.

Motor Boat. Any vessel propelled by an internal combustion engine.

Motor, Compound. A direct current motor which has both a shunt and series field coil.

Motor, Electric. A machine which transforms electrical energy into mechanical energy. Lloyd’s Rules suggest that great care should be taken that generators, motors and electric leads on board ship are not located in such a place that they will influence the compasses.

Motor Generator Set. A combination consisting of an electric motor and generator on the same shaft.

Motor, Main. The large motor direct connected to the line shafting in a vessel fitted for electric drive.

Motor, Series. A direct current or alternating current motor in which the field coil is connected in series with the armature winding, thus allowing the armature current to flow through the series field. The high starting torque and the variable speed of the direct current motor make it specially suitable for cranes and traction purposes.

Motor Ship. A ship driven by some form of internal combustion motor. In its broad sense the term may be considered to include small vessels driven by gas or gasoline engines. It is generally applied, however, to slow cargo vessels having lengths up to five hundred feet and driven by oil engines. For this service oil engine installations have the following advantages over steam or electrical machinery: The elimination of boilers, stoke holds, and coal bunkers with a resultant increase in cargo space. Greatly decreased consumption of fuel. Decrease in the size of operating force with resultant saving in wages. Reduction in machinery space temperatures with resulting increase in comfort and efficiency of operating force. During recent years this type of ship has increased in popularity largely on account of the successful operation of ships already in service.

Motor, Shunt. A direct current motor in which the field coil is shunted across the armature winding. The speed of a shunt motor is practically constant from no load to full load.

Motor, Synchronous. An alternating current motor, the speed of which bears a certain fixed relation to the frequency of the circuit independent of the load on the motor. Such a motor must be brought up to synchronous speed by external means or by a special winding before the field winding is energized.

Mouillage. A French term applied to a vessel’s berth in a harbor.

Mouse a Hook. To pass several turns of wire or small stuff around the point and back of a hook to prevent its unhooking in lowering or canting.

Mousing. The small stuff or wire used to mouse a hook.

Movable Propeller Blades. Propeller blades cast separate from the boss and attached thereto by bolts. These bolts are sometimes worked in such a manner as to permit of a slight adjustment of the pitch of the blade.

Muck Bar. Described under Steel and Iron.

Mud Drum, Boiler. See Boiler, Mud Drum.

Mudhole. A handhole in the mud drum of boilers to provide access for cleaning purposes.

Mullion. A member running parallel with the stiles on a panel door used to receive the inner edges of the panels where two or more panels are used.

Mult-au-matic. An automatic machine designed for boring, facing, turning or threading operations either singly or in combination.

Mushroom Anchor. See Anchor, Mushroom.

Mushroom Ventilator. A ventilator shaped like a mushroom, and designed so that the air will be drawn up under the overhanging umbrella of the mushroom and thence into openings into the vertical pipe leading down into the vessel. The object of the mushroom is to permit access of air but prevent access of water.


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