SHIPBUILDING 



407 



who have done more than any other to popularise 

 and improve the cellular system to reproduce a 

 midship section of the South African mail steam- 

 ship Scot (fig. 5), in which the necessary longi- 

 tudinal strength in the way of girders and inner 

 plating is happily associated with the transverse 

 deep-floor principle, and the whole utilised for the 

 accommodation and manipulation of water-ballast. 



Mild Steel, first used as the build- 

 ing material in France, attracted the 

 attention of the British naval author- 

 ities, and about 1875-76 they ordered 

 from home manufacturers the steel 

 requisite for the construction of the 

 cruisers Iris and Mercury. In 1879 

 the Allan Line entrusted to Messrs 

 William Denny Brothers the building 

 of the Buenos Ayrean, the largest ves- 

 sel of the Allan Line fleet up to that 

 time, the hull of which was of steel 

 bound with steel rivets. Almost from 

 the first, mild steel found favour with 

 the shipyard workers as being a 

 material capable of much easier 

 manipulation than iron, but its high 

 co*t and the exacting test conditions 

 imposed by Lloyd's Registry restricted 

 its use for some years. Improvements 

 in manufacture and enlarged facilities 

 for production, however, gradually 

 cheapened its cost, and enabled Lloyd 8 

 to relax their surveillance. Among the 

 advantages of the new material are its 

 great lightness strength for strength 

 compared with iron, and its effect- 

 ing economy in labour and material 

 through lending itself more than iron 

 to being worked while in the cold 

 state; to being readily and safely 

 flanged along the edges, thus dispens- 

 ing with angle-bars ; and to being 

 supplied in plates of greatly increased 

 size. As regards weight-saving, while 

 the change from wood to iron effected 

 a saving of from 30 to 40 per cent, on 

 the weight of ships' hulls, the em- 

 ployment of steel effected a further 

 economy in weight of almost 15 per 

 cent. Roughly, therefore, the steel 

 ship of to-day is 50 per cent, lighter 

 than a wooden ship of former times 

 of similar dimensions and tonnage. 

 Finally the greater safety of steel 

 ships, or the diminished risk of heavy 

 damage requiring repair, in the event 

 of their getting aground, has com- 

 mended steel to shipowners and 

 marine insurance societies. Through 

 the superior malleability and ductility 

 of the material, steel ships have again 

 and again come comparatively scath- 

 less out of ordeals which would have 

 proved fatal to ships built of iron. 

 At the present time quite 90 per cent. 

 of the shipping produced in Britain 

 consists of steel-built vessels (see table, 

 page 411). 



Composite Ships. The only serious 

 disadvantage attaching to steel ships 

 is one common to them with iron 

 ships fouling and corrosion in actual service. 

 The attachment and growth of marine plants and 

 animals, which takes place more or less rapidly on 

 iron ships in all waters, and especially in warm or 

 tropical seas, has all along been the serious bug- 

 bear of the navigator and the shipowner. Cases 

 are on record where a few months in tropical waters 

 have sufficed to produce such an amount of fouling 



as to reduce the speed of the ship very considerably. 

 The anti-fouling properties of copper-sheathing 

 which from a very early date formed an essential 

 item in the proper fitment of a wooden vessel for 

 sea were so well understood that for long after 

 iron had supplanted wood the ' composite' system 

 of construction was followed. Ships built on this 

 system resemble iron ships in all respects, except 



Fig. 5. Midship Section of us. Scot, illustrating the Cellular Bottom 



System of Construction : 



a, b, arrangement on every frame under engines, and on alternate frames else- 

 where ; c, d, alternate frames in holds. 

 A, keel-plate; B, centre longitudinal; C, side longitudinal (analogous to 



keelsons In vessel* with ordinary bottoms) ; D, wing -plate ; E, bottom frame ; 



F, side frame (reverse frame dotted); O, deck-beams; H, deck-plating; 



I, deck -stringers; K, stringer-angles ; L, deck-planking ; M, hold stanchions; 



N, tank top or inner bottom -plating ; O, bilge keelson ; P, shell-plating ; 



R, deep-floor plates (analogous to solid floors in vessels with ordinary 



bottoms) ; 8, man-holes ; T, air and limber holes. 



that they have wood-planking, keels, stems, and 

 stern-posts ; the wocid-planking enabling their 

 bottoms to be sheathed with copper. The com- 

 posite system of construction found special favour 

 in connection with ships of war and with mercan- 

 tile ships for particular services, intended to keep 

 the sea for long periods and to maintain their speed. 

 The China clippers formerly employed in the tea 



