CHAMBERS'S INFORMATION FOR THE PEOPLE. 



power which is sometimes enormous. As waste 

 of power means waste of coal, and waste of coal 

 loss of money, and as waste of power can only be 

 prevented by building ships in accordance with 

 the conclusions arrived at by scientific men, much 

 more attention is paid to these conclusions than 

 would have been the case had they not affected 

 the purses of shipowners. The result is, that a 

 great improvement in the design as well as the 

 construction of vessels has taken place within the 

 last few years, and no doubt will continue to take 

 place for a long time to come. 



TONNAGE. 



In connection with ships, the word tonnage will 

 be constantly met. It is used in so many differ- 

 ent senses, that it may be well, before going 

 further, to explain its meaning, which may be 

 either displacement, burden, registered tonnage, 

 or builder's measurement. The displacement of 

 a vessel is simply the number of tons of water 

 which she displaces, which is of course exactly 

 equal to her own weight. The load and light 

 displacements are respectively the displacements 

 with and without cargo. Burden is the difference 

 between the light and the load displacement, or 

 the number of tons weight which the ship can 

 carry, in addition to the weight of her hull, masts, 

 &c. The burden includes the weight of the 

 engines, boilers, and coals, so these must be 

 subtracted in order to find the nett burden for 

 cargo. Both displacement and burden are ex- 

 pressed in tons of actual weight that is, of about 

 35 cubic feet each.* The registered tonnage of a 

 vessel, however, is expressed in tons of too cubic 

 feet, and is found by measuring the internal 

 capacity of the ship, and dividing by 100. It is 

 gross or nett, according as it includes or not the 

 capacity of the space occupied by the propelling 

 power. Builder's measurement does not express 

 either the tonnage or capacity of the vessel ; it 

 is founded on a law of 1773, and is a purely 

 arbitrary function of certain dimensions of the 

 ship. Like ' nominal horse-power/ however, it is 

 still retained by buyers and sellers in their 

 transactions. 



DESIGN AND BUILDING. 



In commencing to design a ship, the naval 

 architect generally has given him as data the 

 nett burden of the vessel, her draught of water, and 

 her intended speed. The first part he designs is 

 generally the midship section ; he then draws one 

 of the principal water-lines (or horizontal sections), 

 having previously determined the best proportion 

 of length to breadth for this particular ship j and 

 then proceeds to work out the form of the ship 

 in detail on three small scale drawings, called the 

 sheer-plan, half-breadth-plan, and body-plan. The 

 first of these shews the vessel cut in two vertically 

 from stem to stern, and shews all the water-lines 

 by horizontal, and all the cross sections by vertical 

 lines ; the second is a horizontal section taken at 

 the line of greatest breadth, and shews the true 

 shape of all the water-lines ; and the third shews 

 the midship section, and the true shape of all the 

 vertical sections. It is usual also to construct a 

 small wooden model of the ship from these draw- 



450 



* A ton of water measures about 35 cubic feet. 



ings, which shews the designer what his ship is 

 going to look like better than the flat paper can 

 do. This model is made of a number of hori- 

 zontal layers of wood, and can be taken to pieces 

 at will ; and thus a section of the ship at almost 

 any place can be obtained. From the model and 

 drawings all the lines of the ship are drawn down 

 full size with chalk on the floor of a room called 

 the ' mould-loft ; ' and from these chalk drawings 

 the workmen are guided in the actual construction 

 of the vessel. 



One of the most noteworthy changes in the 

 design of ships which has recently taken place is 

 the gradually increasing ratio between their length 

 and breadth. It is not many years since ship- 

 builders shook their heads over a vessel eight 

 beams in length, and prophesied all kinds of evil 

 for her. Assumptions were made in connection 

 with this subject as groundless as the assumption 

 that because the best speed for a horse drawing 

 a barge was 220 feet per minute, therefore that 

 speed was also the best for the piston of a steam- 

 engine ; yet this was gravely assumed by experi- 

 enced engineers. Messrs William Denny and 

 Brothers of Dumbarton have prepared an interest- 

 ing diagram, which want of space prevents our 

 printing here, shewing the gradual increase in 

 the proportionate length of vessels built by them 

 since 1845. ^ shews at first a length of 6| 

 breadths, it is nearly stationary for some years 

 at 7f breadths, but in 1871-72 it reaches nearly 

 9^ breadths. Vessels are, however, built of even 

 greater length than this. In those of the White 

 Star line especially, a length equal to 1 1 breadths 

 has been used, and found in every way successful. 



Perhaps few changes of similar magnitude have 

 occurred in so short a time as the change from 

 wood to iron as a material for constructing ships. 

 At the present time, the material out of which 

 ships have been constructed since the beginning 

 of the world has been almost superseded in thirty 

 or forty years by the substance which perhaps 

 least of all would have been thought by the 

 ancients suitable for such a purpose.* About 

 wooden shipbuilding, therefore, we need not say 

 much. Shipbuilding yards are always close to 

 the water's edge, and the ships are built endways 

 to the water, with the after-end, or stern, nearest 

 to it. The keel, which is the lowest part of the 

 vessel which corresponds to the backbone of an 

 animal, and from which the ribs or timbers spring 

 is made first, and laid on blocks so arranged as 

 to give it a slight inclination down towards the 

 water. The timbers are next set up, and the cross 

 beams which support the deck, and the whole is 

 finally covered with the planking from bow to 

 stern. When it is necessary to bend a plank for 

 any part of the vessel, it is heated by steam, and 

 then forced into the required shape by screws and 

 levers. The planks are fastened to the ribs by 

 treenails, and the plan is followed of allowing a 

 space or seam between each plank, which is filled 

 up or calked with oakum, and the whole is 

 smeared with pitch. In most cases, the whole of 

 the surface below the water-line is sheathed with 

 copper, which to a great extent prevents its 

 becoming foul through the accumulation of weeds 



* A glance at the table which concludes this article will shew that 

 at present the tonnage of the iron ships annually constructed in 

 Great Britain is about nine times as great as that of the wooden 

 vessels. 





