Online Encyclopedia
Search over 40,000 articles from the original, classic Encyclopedia Britannica, 11th Edition.
PROCESS OF
Online EncyclopediaEncyclopedia Home :: PRE-PYR
del.icio.us it!
|
See also:PROCESS OF See also:DESIGN When a shipbuilder is approached for the See also:production of a new See also:ship, he must be informed of the requirements of the See also:case; the See also:kind of See also:trade or service in which the See also:vessel will be engaged; her See also:speed; if she is to be a See also:steam vessel, the distance she must run on See also:ordinary voyages without recoaling; the See also:weight of See also:cargo to be taken or the number of passengers to be carried, and the kind of See also:accommodation required for them. Very frequently these requirements will include certain limits of See also:size, See also:draught, cost, or See also:tonnage, which must not be exceeded. In addition it must be stated in what society, if any, she is to be classed, as this will determine the details of the scantlings to be employed. The shipbuilder will usually have, to See also:guide him, the details of some successful ship or See also:ships previously built to fulfil the same or similar conditions as in the vessel required, and he will probably know what measure of success or popularity the respective features of the vessel or vessels have earned on service. The dimensions can in this case be at once fixed to provide the necessary speed, strength, stability and seaworthiness, and the cost of the vessel determined. If the departures from some similar ship of known and approved qualities are small, the details of the new ship can be inferred directly from those of the similar ship, and modified drawings, specifications, &c., can be rapidly prepared and the See also:building proceeded with. On the other See also:hand, the departures from previous vessels or the usual practice may be very See also:great, in which case much will depend on the ship-builder's skill and See also:judgment. Outline drawings must first be prepared to the dimensions which may be considered suit-able, and the calculations are made on this assumed design. These will include estimate of the weights of the See also:hull, of the machinery, equipment, &c.; and if it is not intended to class the vessel in some See also:registration or See also:classification society, questions of strength will have to be considered. If, however, the vessel is to be so classed, the determination of the structural strength may be omitted, as the scantlings required by the rules of such society are arranged to provide sufficient strength. If the calculations show that the dimensions assumed do not enable the required conditions to be fulfilled, the dimensions must be modified in the direction indicated by the calculations, and the calculations made over again. This process must be continued until a satisfactory result is obtained. As soon as the dimensions obtained for the vessel are found to be appropriate, more See also:complete drawings are put in hand, and the final calculations pertaining to the displacement See also:sheet, weights of hull and equipment, centre of gravity and See also:trim, metacentric See also:diagram and curves of stability and speed, are made. In the design of yachts the views of the owner, especially if he is a yachtsman of experiencez must necessarily See also:play an important See also:part.
While the See also:present writer was designing the Royal Yacht " Alexandra " he was commanded on several occasions to wait on the See also:late See also: It consists of an elevation showing her See also:longitudinal See also:contour; the positions of the decks; the See also:water-See also:line or line at which she will See also:float, and certain other lines parallel to this and equally spaced below it, which are also called water-lines; a See also:series of See also:vertical lines equally spaced from See also:stem to stern, called "square stations"; and certain other details: of a See also:body See also:plan showing the sectional form of the ship at the square stations, supposing her to be cut by transverse planes at these stations: and of a See also:half-breadth plan showing the form of the ship at the several water-lines, supposing her to be cut by See also:horizontal planes at the levels of these lines-The profile and plans give all the See also:internal arrangements of the vessel, the holds or spaces set apart for cargo, the passenger accommodation, the positions of the engines and boilers, the accommodation provided for the See also:crew, and other principal fittings In a warship there are no cargo holds or passenger accommodation, but the See also:distribution of the armament and magazines, the See also:armour, and other arrangements for the See also:protection of the vessel against injury in See also:action are carefully shown, and the See also:appropriation of every portion of the internal capacity of the vessel is clearly indicated. The midship section shows the structural arrangements of the vessel, and usually the scantlings of the most important parts. The specification is a statement of all the particulars of the vessel, including what is shown on the drawings as well as what cannot be shown on them; the quality of the materials to be used is described, and the scantlings of the same carefully recorded; and it is clearly stated how parts not manufactured by the shipbuilders are to be obtained. When first formed the See also:objects of See also:register See also:societies were simply the See also:maintenance of a register in which was recorded for See also:insurance purposes the main particulars of each vessel's hull, machinery, equipment, &c., together with the names Resist"-of owner, See also:master and builder, as well as a designation tion or class represented by a See also:symbol, which was in- sodetiea. tended to give to underwriters an indication of the strength, durability and general seaworthiness of the ship. As a natural sequence it became necessary for the register societies to formulate rules which would indicate to owners and builders the structural conditions that would entitle vessels to the highest class and the minimum rates of insurance. The register societies now provide the shipbuilder not only with a See also:record of all the important features of the ships which are classed, and thus with much of the information which he requires for the design of his vessel, but they also See also:fix the quality and strength of the material to be used, the scantlings of all the parts of the hull, the riveting of the attachments, the equipment of pumps, anchors, cables, &c., the dimensions and details of the principal parts of the machinery, and all the details of the boilers. Classification societies are thus technical bureaux of the highest value to the See also:shipping community, whose rules are a reflex of the most advanced knowledge and whose methods encourage developments in structural design. - The principal registration and classification societies in 1910, and the number of vessels (sailing and steam) classed, were as follows See also:Lloyd's Register of See also:British and See also:Foreign Ship- 10,302 vessels. ping, having its headquarters in See also:London . British See also:Corporation for the Survey and 710 Registry of Shipping, in See also:Glasgow See also:Bureau Veritas See also:International Register of Ship- - 4,626 ping, at See also:Paris Germanischer Lloyd, at See also:Berlin . , 2,672 Norske Veritas, at See also:Christiania . 1,56o Registro Nazionale Italiano, at See also:Genoa . . 1,263 Record of See also:American and Foreign Shipping, at 1,139 New See also:York . Veritas Austro-Ungarico, at See also:Trieste . 1,041 „ Great Lakes Register . 609 Of these societies, Lloyd's Register, as at present constituted, has existed since 1834; at that date it superseded two See also:rival institutions having a similar See also:object. The name is traced back to Lloyd's See also:Coffee-See also:house, once situated in Lombard See also:Street, in which underwriters met for business purposes, and from which in 1696 they issued their first publication. The first printed register was issued about 1726, a copy dated 1764 being still extant. The See also:office of surveyors is referred to in a register See also:book of the date 1781, but there are evidences that in 1.768 See also:repairs were superintended by See also:officers of the society. In 1799 surveyors were stationed at twenty-four ports in the See also:United See also:Kingdom. In 1822 the register for the first See also:time recorded a steamship. In 1824 appeared the first " Instructions to Surveyors " as to the carrying out the rules for classification; and in 1834, on the See also:establishment of the present society, precise regulations were issued regarding the survey of steamers. An See also:iron ship was built under survey and received a class in 1837, while the first rules for the construction of iron ships were issued in 1855. In 1851 a composite vessel was classed, but it was not until 1867 that rules for the construction of such vessels were issued. See also:Steel was accepted in 1867, experimentally, steel being then made, by the See also:Bessemer process. Steel by the See also:Siemens-See also: The society also publishes yearly a register of yachts, containing full particulars of the yachts of the world and other interesting information, and a register of American yachts, which gives similar particulars of all American and See also:Canadian yachts. All the public proving establishments in the United Kingdom for the testing of anchors and See also:chain cables are licensed by the See also:Board of Trade to carry out these tests under the See also:control of the committee of Lloyd's Register. The See also:assignment of freeboards of vessels, the survey of See also:refrigerating machinery, electric See also:light See also:installation, &c., all come within the See also:scope of the society's operations. The Bureau Veritas was founded in See also:Antwerp in 1828, one of its principal aims being to make known to underwriters the qualities and defects of ships frequenting Dutch and Belgian ports. In 1832 the headquarters were moved to Paris, and in due time its See also:influence spread to all countries where shipowning or See also:shipbuilding existed; it is now represented in over 25o districts comprising about 1500 ports. In 1851 rules were See also:drawn up for the construction of See also:wood ships, and about 1867 for iron. Rules for steel came later, and also rules for the construction of machinery, and, as circumstances arose, See also:provision was made for special types, such as oil-tank vessels, See also:turret vessels, dredgers, &c., as well as for the testing of materials. These rules have been revised from time to time and recently have been remodelled and extended, so as to apply to vessels up to about 900 ft. in length. Special rules have been issued for. vessels intended for See also:navigation in inland See also:waters, for yyachts and for motor boats: A staff of surveyors formed part of the organization from the be-ginning; and in the earlier days the professional experience of the surveyors was the only guide as to what was necessary and sufficient. With the See also:lapse of time, and with increased variety of construction and complication of interests, something more than individual judgment and experience became necessary, and with the Bureau Veritas, as with Lloyd's and other similar societies, definite rules were introduced, and by their means a greater uniformity of practice was attempted and secured. - The British Corporation was founded in 1890, and obtained its See also:charter under the Merchant Shipping Acts for the assignment of freeboards; its first rules were issued in 1893. Its inception was due to the enterprise and influence of a number of leading shipowners, shipbuilders and engineers throughout the country, and more particularly in Glasgow and the See also:West of See also:Scotland, the first aim of the founders being to provide an See also:independent society, thoroughly capable of dealing with the complicated questions which were likely to arise under the Load Line See also:Act then coming into operation. The Liverpool Registry, which' had once been independent, had been absorbed into Lloyd's Register some years before,, and it was thought that the enormous shipbuilding interests of the country demanded the existence of a society whose friendly rivalry with the great society of Lloyd's Register would have a beneficial influence on the shipbuilding of the country. Owing to the See also:comparative See also:absence of small vessels the relatively small number of the vessels on theregister represents 2,331,000 tons. The society is controlled by a committee of See also:forty members—shipowners, shipbuilders and underwriters—and; in addition, there is a branch committee in See also:Italy. There is a staff of 135 surveyors distributed over the principal home and foreign ports. The Norske Veritas was established in 1864 by the various marine.. insurance clubs of See also:Norway. Previously each See also:club had its own See also:separate staff of surveyors, on whose report to their club depended the class of the vessel and the See also:premium to be paid. As ships See also:rose in value and reinsurance became the See also:rule, something had to be done for mutual protection. By the establishment of the Norske Veritas one See also:uniform See also:system of classing and valuing was substituted for the older methods. In the See also:matter of rules this society kept See also:pace with the changes of the See also:mercantile marine; it provided, as the occasion required, for the introduction of iron and steel- in place of wood, and of steam in place of sails. The Germanischer Lloyd was established in 1867, and reorganized as a See also:joint-stock company in 1889. Its functions are carried out by officers at the central office in Berlin, assisted by a staff of 50 ship and See also:engine surveyors in See also:Germany and 120 at the principal foreign ports, the latter under control of agents, who are mostly consuls, " In all foreign parts in which the Germanischer Lloyd has no representative, the See also:German consuls are required by order of their See also:government to exercise the functions of an See also:agent of the Germanischer Lloyd." The Registro Nazionale Italiano was formed in 1910 to take over the Registro Italiano, which was founded in 1861. The society has adopted the rules of the British Corporation Registry, has a staff of surveyors in Italy, and has an arrangement with the British Corporation which enables them to utilize the services of the surveyors to that society in British and foreign ports. The Record of American and Foreign Shipping; was established in 1867 by the American Shipmasters' Association (now called the American Bureau of Shipping), and is the See also:standard American authority. Its rules for the construction and classification of vessels, as published in 1889 and amended in 1900, received the approval of the U.S. See also:Navy See also:Department and of the several boards of American underwriters. It has agents and surveyors in many of the principal ports of the world. The present rules and tables of most of the above societies apply to construction in steel. Lf iron is to be used in-the construction of vessels, the material must be increased in thickness from Jo % tq 25%, dependent upon the part for which it is to be used and the quality of the iron. In some eases separate tables for steel and iron accompany the rules, and in a few cases the societies provide rules for construction in wood. The-latest rules of Lloyd's Register provide only for steel ships, but vessels of wood and iron are still classed. The highest class assigned, upon completion of a ship by the societies referred to, is as follows : Lloyd's iooA i 1114L.M.C.. Bureau Veritas . +@ 3/3L I.I. British Corporation B.8.-* . M.B.B. Vi .irps Norske Veritas zAz * M & K,V. Germanischer Lloyd . + zooA + M.C. Record of Amer. Shipping The See also:star or See also:cross in each case denotes special survey. In Lloyd's Register IooA refers to conformityof scantlings with the tables; the figure 1, to the efficient See also:state of the equipment, including anchors and cables; L.M.C. denotes Lloyd's Machinery Certificate. In the Bureau Veritas the large I expresses first See also:division of classification (out of three) ; the two rings around the denote that the ship is divided into a. sufficient number of water-tight compartments to enable her to float in still water with any two of them in See also:free communication with the sea. Very few ships in the register have the See also:double See also:ring, but some have a single ring ® denoting See also:power to float in still water with any one compartment in free communication with the sea; 3/3 expresses completeness and efficiency of hull and machinery; the See also:letter following 3/3 indicates the navigation for which the vessel is intended ; the first t, that the wood' portions - of the hull are entirely satisfactory.; while the second I has the same significance in respect to the equipment of masts, spars, See also:rigging, anchors, chains and boats. In the British Corporation Register, B.S. signifies conformity with all requirements, these letters See also:standing for British Standard; M.B.B. signifies that the machinery also conforms. In the Norske Veritas 1AI denotes compliance with rule requirements as regards the hull. M & K.V. signifies that the vessel has a Norske Veritas certificate for engines and boilers. The third figure t denotes the efficient state of the equipment. In the Germanischer Lloyd the See also:mark too A signifies that the ship which bears it is, including her equipment, up to the requirements of the highest class of the society. The figure 4 signifies that the class is to be regularly renewed after special surveys held iii periods of four years each. M.0 -signifies AI M.C. that the machinery also conforms with the requirements of the rules and has obtained a separate certificate. Certain steam vessels ol?See also:tain a Ej which encloses the '1` in front of the class mark. This signifies that the arrangement of the water-tight bulkheads is such as theoretically to ensure the floatability of the ship when the sea has See also:access to one or two of her compartments. The tests for steel material to be used in building the ships, as required by the same societies, may be tabulated as follows:appointed by the British government, and one of , the questions considered was that of the load line. In the final report1874the conclusion was arrived at that a See also:settlement of a load line should, in the main, be guided by reserve buoyancy as a first See also:consideration. The commissioners were, however, of See also:opinion that an act•of See also:parliament, framed to enforce any scale of See also:freeboard, would be mischievous, if not impossible, as would be any universal rule for the. safe loading of merchant ships. In 1874, in a See also:paper read before the Institution of Naval Architects Ultimate Tensile Strength. See also:Elongation in Length of 8 in. Temperature Test. Lloyd's Register . . Between 28 and 32 tons per Not less than 20 % for plates See also:Sample heated to a See also:low See also:cherry British Corporation sq. in. a in. thick and upwards. red and cooled in water at Registro Nazionale Italiano 11 11 „ 8q° F. and doubled over a Norske Veritas Between 27 and 32 tons per • „ See also:radius of i i times the thick.. Bureau Veritas . . sq. in. ,, ness of ,the See also:plate tested, Record of American Shipping . . Between 58,000 and 68,000 lb 22 % for plates weighing 18 lb Germanischer Lloyd . per sq. in. per sq. ft. and upwards. Between 26 and 31 tons per 20% for plates lo mm. in sq. in. thickness and upwards. For plates less thane in. in thickness the first four societies in the by Mr B. Martell, who was then the See also:chief surveyor to Lloyd's Register, above table allow an elongation of 16%; the Bureau Veritas allows i tables of, freeboard were sug ested from data collected at all the an elongation varying between 2o% and re% for plates between i-bths and S,oths of an See also:inch in thickness; the Record of American Shipping allows an elongation of 18% for plates weighing less than 18 lb per square See also:foot; the Germanischer Lloyd allows an elongation of 16% for plates between io mm. and 5 mm. in thickness and 14 % for plates less than 5 mm. in thickness. For steel plates to be flanged See also:cold Lloyd's Register and the British Corporation require a minimum tensile strength of 26 tons, and for sectional material such as angles, bulb angles and channels the tensile strength may be as high as 33 tons. For See also:rivet steel the tensile strength must be between 25 and 30 tons per square inch, with a minimum elongation of 25 % on a See also:gauge length of eight times the See also:diameter of the See also:bar. Hot and cold bending and forge tests for See also:angle bars are also prescribed. The regulation of certain matters connected with the design of merchant ships falls upon the Marine Department of the Board of oarrd of Trade. The authority of the Board is the Merchant B See also:Boa Shipping Act of 1894, which consolidated previous ~~h enactments. These matters include the measurement See also:vision. of tonnage, and provision for the safety and comfort of passengers and crew. The former is discussed in a separate See also:article (see TONNAGE), but it may be mentioned here that the following countries have at various See also:dates accepted the British rules for tonnage: United States, See also:Denmark, See also:Austria-See also:Hungary, Germany, See also:France, Italy, See also:Spain, See also:Sweden, See also:Netherlands, Norway, See also:Greece, See also:Russia, See also:Finland, Hayti, See also:Belgium and See also:Japan. The amount of See also:deduction for propelling power varies in Spain, Sweden, Nether-lands, Greece, Russia and Belgium, but See also:option is granted to owners to have the engine-See also:room remeasured under the rules of See also:allowance for engine-room See also:relating to British ships. Special certificates are at present also issued, on application, to vessels trading to See also:Italian ports, as the Italian authorities do not at present recognize certain sections of the Act of 1894 in regard to deductions from tonnage and exemptions from measurement. Special tonnage certificates are also issued for the See also:Suez See also:Canal, where the measurements of ships and deductions from tonnage vary from British rules, and are detailed at length by the Board of Trade in their Instructions to Surveyors. With regard to safety and comfort the surveyors have to see, among other matters, that the crews are properly accommodated and the passengers not too crowded; that the boats and See also:life-saving appliances are sufficient; that the See also:lights and signals. are in order; that the freeboard is sufficient and ship otherwise seaworthy; that See also:grain cargoes are properly stowed; and that See also:coal cargoes are adequately ventilated. Any question of doubt as to the strength of passenger vessels has to be referred to the Board of Trade, and in future midship sections, with all particulars marked thereon, are to be submitted in the case of all new steamships building under survey for which passenger certificates are required. A passenger certificate is required whenever a steamer carries more than twelve passengers. In granting it the Board of Trade recognizes five different services, ranging from foreign-going steamers to excursion steamers in smooth water. The Board of Trade rules for scantlings are not published officially.
A See also:Bill, introduced into parliament in 1869, dealing with the load line question, contained a clause requiring the draught of water to be Load line recorded at which a vessel is floating when leaving See also:port. Load See also:lie This Bill did not pass; but in the following See also:year the
Merchant Shipping See also:Code Bill was brought in, containing board. the same provision, and, in addition, requiring a stale showing the draught of water to be marked on stem and stern See also:post of every British ship. This became See also:law in 1871. The same Act empowered the Board of Trade to record the draught of water of all sea-going ships on leaving port by surveyors duly authorized. In See also: The provisions of the 1875 Act were See also:con-firmed by a more comprehensive Act in 1876, which extended the compulsory marking of the deck line and disk to all British ships, except those under 8o tens engaged in fishing and the See also:coasting trades, also excepting, yachts or See also:war vessels. Before this Act was passed the Board of Trade took action, by appointing a committee to consider the possibility of framing rules for the regulation of freeboard. The committee was to be composed of representatives of the Board of Trade, Lloyd's Register, and the Liverpool Under-writers' Registry. This See also:attempt to establish an authorized scale of freeboard failed. Meanwhile the subject was not lost 'sight of;the collection of data was continued, investigations were carried out, and six years later (in, 1882) the committee of Lloyd's Register issued freeboard tables, and undertook to assign freeboard, on the basis of the tables issued, on owners making application for the same. In the course of three years 944 vessels had freeboard§ thus assigned to them, and in the case of 775 of this number the owners voluntarily accepted the freeboards assigned. In See also:December i883 the Load Line Committee was appointed by the Board of Trade; and after two years' careful deliberation and investigation, involving 'much labour, the committee presented its report. This report was accompanied by tables, which agreed closely with those previously issued by Lloyd's Register; and they were accepted by the committee of that society in See also:September 1885. Between 18.85 and See also:June 1890 (the latter being the date the Load Line Act was paassed) 285o steam and sailing vessels had freeboards fixed by Lloyd'e'Register, and of these 2520 were taken from the tables. After the passing of the Act in 1890 appointments to assign freeboards were granted to Lloyd's Register, Bureau Veritas and the British Corporation. In 1893 the See also:original tables ivere' modified with respect to some 'of the ports in the United States on the See also:Atlantic, the sailing from or to which in the See also:winter was to subject the ship to a few' inches additional freeboard. In 1898 they were further modified 4a) to exempt ships over 33o ft. in length from the additional freeboard just Yuen= tioned, and to limit the additional freeboard in smaller ships; (8) tq give some concession to turret-deck steamers; and (c)'insome other See also:minor matters. In 1906 the Shipping See also:Laws were amended so that all foreign vessels loading at British ports required to be provided either with a'fteeboard assigned under the British tables, or under tables of a;foreigp country which had been certified by the British Board of Trade being equally effective with the British freeboard tables.
In the same year the British tables were revised throughout in the light of the experiences of previous years of See also:practical See also:administration,, by a committee whose members were drawn from the Board of Trade and the three assigning bodies—Lloyd's, British Corporation, and the Bureau Veritas. Important modifications were
s
960
made in the freeboards for vessels with complete superstructures or'a considerable extent of strong deck erections, and in those for large vessels, with the result that a considerable increase was given to the carrying capacity of British shipping. This was followed by a See also:conference in See also:Hamburg between eight delegates nominated by the British government—being practically the former committee—and eight German delegates. The conference resulted in an See also:adjustment of the German freeboard tables previously in force, and Germany has adopted freeboard tables and regulations which are recognized by the British government in an Order in See also:Council dated 2I stNovember 1908. France and See also: By deck cargo in this section is meant any deals, battens or other wood goods of any description to a height exceeding 3 ft. above the deck. In 1890 a committee was appointed by the Board of Trade to See also:deal with the spacing and strength of transverse water-tight bulk-heads and to make recommendations. The first matter submitted to this committee related to subdivision which should enable a ship to float in moderate See also:weather with any two compartments in free connexion with the sea. The committee, while recommending the above as a standard for sea-going ships of not less than 425 ft. in length, and for cross-channel steamers irrespective of length, suggested less stringent conditions for sea-going ships of shorter length. There was no See also:suggestion of enforcing such subdivision by law; but as a See also:reward for complying some concession was to be allowed, under the Life Saving Appliances Act of 1888, as to the boats or life rafts to be carried. On the presentation of the report the matter was, however, allowed to drop, and the rules of Lloyd's Register and the other classification societies are therefore the only rules with practical influence. The subdivision required by Lloyd's Register for all steamers comprises a bulkhead at each end of the machinery spaces, and a bulkhead at a reasonable distance from each end of the ship, making four in all. In addition for larger steamers other bulkheads have to be fitted, making the total as follows, namely Length of Steamer. Bulkheads. 285 ft. to 335 ft. 335 ++ 405 6 405 + 470 ++ 7 470 ++ 540 8 540 „ 6io „ . 9 6io „ 68o „ Io The positions of these additional bulkheads, and the height to which they are to be carried, are clearly stated, and the rules are given for their scantlings. These scantlings are suitable for purposes of safety in the event of See also:accident; but it is understood that they have to be considerably increased when the bulkhead is also used to withstand frequently the pressure of oil or water See also:ballast; a deflection of the plating which would do no harm in an emergency once en-countered would certainly become serious if often repeated in the ordinary service of the ship. The foremost bulkhead of the ship receives the name of collision bulkhead, or sometimes fore-See also:peak bulkhead; the aftermost, the after-peak bulkhead. In sailing ships the collision bulkhead alone requires to be fitted. PRACTICAL Practical shipbuilding requires a knowledge of the properties of the materials used in the construction of ships, and of the processes by which they are produced or prepared for use, so that they may be suitably selected for the services for which they are [PRACTICAL intended; also a knowledge of the methods, means and machinery by which, after delivery in the shipyard, the materials are brought to the requisite shape, erected in their proper relative positions, connected together, and completed so as to form a structure which shall fulfil the intentions of the design, whether large or small, merchant ship or warship. The varieties of ships are very great, and are constantly changing, and thus new problems continually present themselves to the shipbuilder. There is also an ever-increasing demand for rapid production, which necessitates a rigorous and See also:constant See also:search for simplification of methods of work, for labour-saving and time-saving machinery, for improved means of handling material in the shipyard, and for workshops and factories which will more completely prepare and finish their various products before despatch to the shipyard. Whatever the size of the ship or the type to which she belongs, the general principles of construction remain very much the same in all cases. The following See also:account applies to steel and iron shipbuilding. The exterior parts—the bottom, structural sides and decks—See also:supply the strength required for the pans. structure as a whole. The bottom and sides are spoken of as the See also:shell or outside plating, and are, with the decks, kept to the proper shape by means of frames See also:running across the ship, like the rafters in a roof or the ribs in the body. These are called transverse frames or ribs, and beams where they run under the decks. The parts of the frames at the bottom of the ship, where they are made deep and strong to support her when she is docked or grounded, are known as floors, while the spaces between these floors are spoken of as the bilges. The transverse frames and floors are held upright in their proper relative positions by other frames which run lengthwise in the ship; one at the See also:middle line being called the centre keelson, and others fitted at the sides, keelsons, See also:bilge keelsons and side stringers. All the fore-and-aft frames, taken together, are spoken of as the longitudinal framing. Where tanks for carrying water ballast are built into the bottom of the ship, the centre keelson is called the centre girder, and the keelsons or bilge keelsons the side girders. In large merchant vessels, and in all war vessels, except the smallest classes, an inner bottom is provided for increasing the See also:security against injury by grounding, and against ramming and See also:torpedo attack in war vessels, in addition to forming tanks for carrying water, either as ballast or for use in the ship. In such cases the centre keelson is called the vertical See also:keel, and the keelsons and girders are called longitudinals. When the deep vertical transverse plates forming the floors only extend between the keelsons, girders or longitudinals, and are attached to them by angle bars, the floors are called intercostal floors, and the keelsons, girders and longitudinals are said to be continuous; on the other hand, when the keelsons, girders or longitudinals extend only between the frames and floors they are called intercostal keelsons, girders and longitudinals, and the frames. and floors are said to be continuous. In war vessels, except the smallest classes, much of the longitudinal framing is continuous; and the transverse framing, for the most part, is built up of angle bars upon the See also:outer bottom and under the inner bottom, with short plates, called See also:bracket plates, between them, attached to the longitudinals by short angle bars. Frames built up in this way are called bracket frames. In mercantile vessels the transverse frames both within and without the double bottom are usually continuous. Besides the transverse and longitudinal framing, there are partitions used for dividing up the internal spaces of the ship, which are called bulkheads; they are partial, complete, water-tight or non-water-tight, as the circumstances of the case require. In warships the transverse bulkheads are so numerous, in order to restrict as much as possible the entrance of water from damage in action, that they go a See also:long way towards providing the necessary transverse strength, and the transverse frames are consequently made of thinner materials and fitted at greater distances apart than they otherwise would be. Transverse frames are from 36 to 48 in. apart in large warships, and from 24 to 33 and some-times 36 in. in large merchant ships. At the extreme ends of the ship the shell plating on the two sides is attached to forgings or castings, which are known as the stem at the fore end, and the stern See also:frame or sternpost at the after end. The stem of a warship is generally made very massive, and projects under the water so as to form the See also:ram. The longitudinal framing is carried right forward and aft when possible, and the ends of the several frames are connected together across the ship by strong plates and angles, which are called knees or breasthooks, forward; and knees or crutches, aft. Additional supports, introduced to enable the vessel to withstand the heavy blows of the sea in See also:bad weather, are called panting stringers, panting knees, and panting beams, panting being the See also:term applied to the movements which occur in the side plating The sections of the iron and steel bars in See also:common use are shown in fig. 75, and are named as follows: A. Angle bar. E. I bar. j. Half-See also:round B. T (Tee) bar. F. See also:Plain bulb bar. moulding.' c. Channel bar. G and H. Angle bulb. K. Hollow D. Z (Zed) bar. I. T bulb bar. moulding. The vertical, or central, portion in the I, T and bulb sections is spoken of as the See also:web, and varies from about 3 in. to 9 in. in See also:depth ; the horizontal parts are called flanges; in an angle bar, both parts of the section are called flanges. The flanges vary in width from about 2 in. to 7 in. in the angle bar, and from 3 in. to 6 in. in the others. The thickness varies from about } in. to t in. These dimensions taken together are called the scantlings of such material. The thicknesses of the plates in common use generally lie between c e I if sufficient strength is not provided. Where the ends of the ship are very full, or See also:bluff, the frames are sometimes inclined, or canted out of the transverse See also:plane, so as to be more, nearly at right angles to the plating; such are known as cant frames. At the stern a transverse frame, called a See also:transom, is attached to the upper part of the sternpost to form a See also:base for cant frames of the overhanging part of the stern which is known as the See also:counter. To assist the beams and bulkheads in holding the decks in their proper positions, vertical pillars are introduced in large See also:numbers; but to avoid the loss of space and inconvenience in handling cargo, ordinary pillars are often dispensed with, and special pillars and deep deck girders are fitted instead. The steel generally used in shipbuilding is known as mild steel. It is very tough and ductile, and differs from the hard steel, out of materials. which tools are made, in that it will not take a See also:temper, i.e. if heated and plunged into oil or water, the sudden cooling has very little effect upon it, whereas with See also:tool steels a great See also:change takes place, the steel becoming very hard, and usually brittle. This quality of tempering depends chiefly on the amount of See also:carbon in the steel, mild steel containing less than •25 %. Steel of greater strength than mild steel is used occasionally in certain parts of warships. The extra strength is obtained generally by the addition of carbon, See also:nickel or See also:chromium, coupled with special treatment. The quality of the plates and bars used is tested by cutting off strips about 2 in. wide, and bending them double by hammering, or in a See also:press, until the See also:bend is a semicircle whose diameter is three times the thickness of the See also:strip. The strips are sometimes heated and plunged into water to cool them suddenly before bending, and they may be cut from either side or the end of the plate. Strips are taken occasionally and hammered into various other shapes while hot and while cold, so as to ascertain the general quality of the material. To ensure its tenacity, strips are taken and machined to give a parallel part about 2 in. in width, of at least 8 in. in length. Two centre-See also:punch marks are made 8 in. apart, and the strip is secured in a testing-See also:machine constructed so that the ends can be gripped by strong jaws which do not injure the parallel part. The jaws are then gradually pulled apart, the amount of the pull required to break the strip being registered, and also the extent to which the strip stretches in the length of 8 in. before breaking. The tensile strength varies between 26 and 32 tons per square inch, calculated on the original sectional See also:area of the parallel part before breaking, and the elongation in the 8 in. is about 20%. The standard strength and elongation required by the principal registration societies have already been given. The steel used for making rivets is similarly tested ; and samples of the finished rivets are also taken, and hammered into various shapes, hot and cold, to ensure that the See also:metal is soft and ductile and suitable for the work. The stem, stern-frame, &c., are frequently made of forged iron; but if of steel, they are See also:cast to the form required. These castings are tested by being let fall on hard ground and then slung in chains and hammered all over, when faults of casting are generally discovered by See also:variations in the sounds produced. By this hammering the general soundness of the casting is ensured. To test the quality of the steel in the casting, small pieces, which are cast on for the purpose, are removed and tested in the same manner as just de-scribed for the strips cut off from the plates; they are required tO give about the same tensile strength, but a little less ductility, say in % instead of 20 % elongation in 8 in. xxty. 3175• t in. and r in. Thicker or thinner plates are obtainable, but are not often used for merchant ships. These plates are of varying sizes as required, the tendency being to use very large plates where possible, and widths of 5 ft. to 7 ft. are used in lengths of from 40 tO 20 ft. Angle bars are used in4engths of from 20 to 8o ft. as required, or as may be limited by the means of transport between the steel See also:works and the shipyard. The various plates and bars are connected together by means of rivets of various forms. Specimens of the common kinds are shown in fig. 76. The heads and points have distinctive names, as follows: (A) Countersunk head, chipped flush. (B) Ordinary countersunk head. (c) Snap head. ft.) Snap head with conical or swelled See also:neck. E) See also:Pan head with conical or swelled neck. (F) Pan head. (G) Countersunk point. (x) Rough hammered point. (1) Snap point, hand work. (j) Snap point, machine work. The pan head rivet (E) with conical or swelled neck is the most commonly used, as it is convenient to handle and gives See also:good See also:sound work. The rough hammered point (it) is also very commonly used, is very effective and is readily worked. The pan head (F) and snap head (c), without cones under the heads, are only used for small rivets; the heads (A), (B), (c), (n), are used where considered desirable for See also:appearance' See also:sake, but (c) and (n) are also adopted when the riveting is done by See also:hydraulic machinery, in which case the snap point J is also used. The countersunk point (G) is used on the outside of the shell, and in other places where flush work is required. The snap point (1), for internal hand riveting, is used where desired for appearance, instead of the rough hammered point. The rivets vary in diameter from about f in. to it in., and the lengths are as required to go through the holes and give enough material properly to form the points. The diameter of the rivet is settled according to the thickness of the plates to be connected, being generally about t in. more than the thickness of the separate plates. The distance from centre to centre of the rivets is spoken of as the See also:pitch, and is generally expressed in diameters. For connecting plates and bars in the framing, the pitch of the rivets runs gefierally to 7 diameters; for securing edges which must be water-tight, the pitch is from 43 to 5, and, if they are to be oil-tight, 3 to 3j diameters. In butts and edges of shell-plating the pitch varies from 3i to 4i diameters. II H II In some positions rivets like the above cannot be driven into place and properly hammered up; resort is then made to rivets which have screwed points, called tap rivets, shaped as shown in fig. 77. That shown at (a) is used where it is necessary to make the See also:surface flush, but not necessary to re-move the rivet for examination of plating; and when See also:hove right up, the square head is chipped off and the surer See also:face hammered smooth. In other positions pat-terns (A) or (c) be most suitable. The See also:machines used in the shipyard have been ir,,uch improved of See also:recent year's. The one most used is the punching and shearing Machine machine, on one side of which plates of all thicknesses up :oats. to 2 in. may be cut or sheared to any desired form, while on the other side rivet holes maybe punched of any required size. Special See also:shears are provided with V-shaped cutters for shearing angle bars, but in some cases the cutters of ordinary shears may be replaced by V-shaped cutters for this purpose. When the plates and bars leave the shearing and punching machine their edges are rough and slightly distorted, to remove which it is necessary in many cases to plane them. This is usually done by special machines provided for the purpose. In the most See also:modern types the cutters are duplicated and the machine arranged to cut both ways. When it is required to cut a square edge on the flange of an angle bar to facilitate caulking, a pneumatic chipping machine of recent introduction is frequently used, but this is more usually done in a planing machine. In shipbuilding a great deal of drilling must be done by hand, but, where it is possible, drilling machines are employed. The most modern forms can See also:drill a number of holes at the same time. For countersunk work it is necessary to make the hole See also:funnel-shaped, as will be seen from fig. 77. This shape is rapidly given to the holes already punched or drilled by means of a special drilling machine, which can be very easily ' and rapidly manipulated. .The use of portable drills, to avoid hand labour, is rapidly increasing, and several types are in use, operated by electric See also:motors, compressed See also:air or flexible shafting. They are carried to any position required. The hole made by a drill is cylindrical, but that made in the process of punching is conical. On one side of the plate its diameter is determined by the diameter of the punch, and on the other by the diameter of the See also:die, which must be greater than that of the punch. This See also:taper tends to produce close and sound riveting, as the joint is closed both by the knocking down of the rivet and by the contraction of the rivet on Cooling. On the other hand, the operation of punching injures the steel in the neighbourhood of the hole, and for work subjected to great stress this deteriorated material must be removed by countersinking or by drilling the hole to a larger size, or the quality of the material may' be partially restored by See also:annealing. The process of annealing consists in See also:heating the steel to a good red, then allowing it to cool very slowly; during this process parts of the material which have been unduly distressed in working regain their strength by,molecular rearrangements in the distressed parts. This process occurs to some extent when hot rivets are introduced into the holes and hammered up. The steel immediately adjacent to the rivet' is heated, and afterwards cools gradually as the See also:heat becomes distributed into the body of the plate. In some experiments carried out by the See also:Admiralty in See also:Pembroke Dockyard in 19o5, it was found that the effect of punching holes close together, as for a See also:butt-strap, was to diminish the tensile strength of the plates about Io%; that hot riveting restored about half of this; and that when holes were drilled and countersunk right through, also when holes were punched i in. and countersunk right through, so as to enlarge hole to $ in. in diameter, there was no loss. In addition to the . machines mentioned above, many special appliances have recently been introduced into shipyards for the purpose of economically carrying out definite operations rendered possible by the use of mild steel. Ships built with a bar keel require the garboard strake plates on each side to be flanged on one edge, so as to See also:fit against the bar keel. This flanging was formerly carried out by heating the plates and treating them hot, but now a very powerful machine, called a keel-plate bending machine, and usually worked by hydraulic power, is employed for the purpose with the plate cold. Flanging plates cold has also become general for a variety of , pur- poses. In.a, bulkhead, stiffening is necessary, and for this purpose angle bars, were commonly used; the horizontal stiffeners are now frequently formed by flanging the See also:lower edges of the plates. Instead sf fitting an angle bar to connect two plates at right angles to one another, the edge or end of one may be flanged, and half the weight of the angle ,bagand the rivet work saved. For all such work some-what lighter flanging machines than the keel-plate bending machine are used ; they are generally worked by hydraulic power, but there is no difficulty in See also:driving them by any other means. Another modern appliance is the scarfing machine, which is used chiefly in connexion with the lapped butts of shell and other plating. Before its introduction it was usual to bring the ends of the plates together and See also:cover the joint with a short plate called a butt-strap, secured to both plates with a proper arrangement of rivets (see fig. 78). It is now more usual in merchant ships to work overlap butts, some half of the weight of the butt-strap and riveting and other work being saved thereby, although the appearance may not be quite so sightly. The difficulty with this system is that the passing plates on each side have their edges lapped over the ends of the See also:lap-butt, and in order that they may be brought close some machining is necessary; this is called scarfing, i.e. slotting away the corner of the projecting butt so as to produce smooth surfaces for the side laps (see section at A B, fig. 78). The machine used for this operation is a slotting machine with two heads, so as to slot both edges of the plate at the same time; it is provided with a table which can be adjusted to the necessary See also:bevel, so that the slotting tools may reduce the thickness of the edges operated on in a See also:gradual taper to a See also:knife-edge. A more recent appliance for reducing weight is the joggling machine. As already described, the usual method of working the shell-plating is by alternate inside and outside strakes of plating, the outside plates overlapping the inside plates, and the space between them and the frames being filled in by slips or liners. These liners throughout the ship amount to a considerable weight, and the object of the joggling is to do away with the See also:necessity for them. This is effected by shaping the outside plates as shown in section b. fig. 79. Sometimes the frames are joggled instead of the plates, as shown in section c, fig. 79; the inside plate lies in the recessed portion of the frame formed by the joggling process, and the outside plate on the unrecessed portion, its edge lapping over the edge of the inside plate the usual width. The angle bar in this case must be heated, and the hydraulic press is placed so as to be readily accessible for the handling of the part to be heated. The system of joggling the frames has not been adopted to nearly so large an extent as that of joggling the plates. Frame-bevelling machines appear to be growing in favour.' The machine is placed on rails, near to and across the mouth of the frame See also:furnace, so that it can be readily placed in position for the frame bar to be drawn out of the furnace directly through it, and moved to one side when not required. In the machine a series of rollers, which can be inclined to suit the varying bevel required, operate on the bar. The inclination of the See also:roller is varied as the bar passes along, a See also:dial and pointer giving the angle of bevel at each instant. As the bar passes through, the workman, with his, See also:eye on the dial, manipulates the machine so as to give it the required bevel. It is afterwards completed on the slabs, the form being taken from the strive-board in the usual way. The shipyard should be supplied with modern machinery of the most approved type, in order to produce the best work at economical rates: rolls for straightening and bending plates, for fairing and bending beams and angle bars; shaping and slotting machines; lathes and milling machines; heavy planing machines. It should also have a blacksmith's See also:shop, saw-See also:mills, joiners' shops, &c., all fully equipped for completing, as far as possible, the work of the yard. The workshops and machines should be distributed so that, as far as possible, the material moves steadily along, as the various operations are performed upon it, to its place in the ship. Pneumatic tools are often preferred for light work, such as chipping, drilling, rimering and caulking; they are also occasionally used for riveting, but they are not yet much in favour for this class of work. Hydraulic power is particularly well adapted for heavy presses, such as for keel-plate flanging, for punching and shearing, and especially for punching manholes and lightening holes in plates, and for heavy riveting. It is also very successfully applied for pressing to shape a great variety of small fittings made of steel or iron. For such machines as rolls, ordinary shears and punches, winches, &c., separate steam engines are still frequently fitted, but there is a very marked tendency to replace all these by electric motors. Electric power for driving all the machinery has been introduced into many ship-yards. It has many advantages: all the power required in the yard may be generated in one building in any position, containing the boilers, steam engines and electric generators, and the whole may be designed and worked so as to secure great See also:economy. The current is supplied either to motors directly driving the heavier or outlying machines, or to motors driving a line of shafting where the machines are of a lighter character and are arranged in compact See also:groups. Fixed machines can beplaced where most convenient for the work, without any reference to the position of the boilers or other machinery, and a large number of machines can be very readily made portable for the lighter classes of work. The power may be transmitted with but little loss, whereas with steam-driven machines at a distance from the boilers, lines of steam piping must be introduced, and loss of power is entailed. The saving which the system of electric driving effects over that of .steam driving in the See also:consumption of coal in a large shipyard is considerable, and is claimed by those who have adopted it to be sufficient to justify the large See also:capital See also:expenditure required to convert a shipyard from the latter system to the former. As the plates, beams, angle bars, Z-bars, &c., are delivered, they must be stored in convenient racks, with marks showing for what purpose they are intended, so that they can be readily identified hoisting, except for plates under the bottom and counter, where a and removed without loss of time. Additional information and CommentsThere are no comments yet for this article.
» Add information or comments to this article.
Please link directly to this article:
Highlight the code below, right click, and select "copy." Then paste it into your website, email, or other HTML. Site content, images, and layout Copyright © 2006 - Net Industries, worldwide. |
|
|
[back] PROCESS |
[next] PROCESSES FOR GAUGING |