304 



NA TURE 



[jULY 25, 1907 



designs and tenders, which is uflcn very short. This is 

 of the nature of enginecrin;; \voil< of all kinds. 



The nature of some of the principal problems that arise 

 in the design of ships, and the extent to which their 

 solutions are scientific, empirical, or merely tentative, will 

 he indicated in some degree as I go on. I pass over 

 what 1 venture to call the secondary problems of mensura- 

 tion and hydrostatics — which relate to bodies floating in 

 ('i|uilibrium in still water, and constitute the bulk of the 

 ship-designer's purely scientific stock-in-trade — and will 

 endeavour to direct attention to some of the fundamental 

 problems of a ship's behaviour at sea. I do not under- 

 r.ite, however, the great importance of those passed over, 

 (or it is the results of mathematical and physical research 

 into the still-water properties and conditions of floating 

 bodies which enable us, with the aid of observation 

 and experience, to judge the probable qualities and 

 behaviour of ships at sea. They also furnish the best 

 data for comparisons between ships of varying dimensions 

 and forms. 



The class of problems that demand attention fir.st are 

 those which bear the most directly upon safety at sea. 

 1 hese are very general and comprehensive in character, 

 .md are impossible of anything like complete solution from 

 the purely scientific side; but they are of vital importance, 

 and solutions of them, which will be upon the right side, 

 have to be found somehow for everv ship that is 

 built. 



The first in natural order of the problems that relate 

 to safety is the maximum depth of safe loading, or the 

 minimum sea-going freeboard for a ship of anv given size 

 or type. 



The losses of cargo-steamers, and of lives at sea, became 

 so serious twenty-five to thirty years ago that many 

 attempts were made to get a law passed for limiiin" depth 

 of loading. The great difficulty and complexitv '^of the 

 problem resisted for a long while all efforts to deal satis- 

 factorily with it. It was considered by many authorities, 

 upon all sides, to be impossible of solution ; and yet 

 individual shipowners, or shipping companies, were obliged 

 to regulate the loading of their own ships in some wav, 

 and upon some system, or make it the duty of others 

 fo do so. It followed, therefore, that if the knowledge 

 and experience of tho.se separately responsible for the 

 loading of the various types of vessels could be brought 

 together and analysed, it ought to be possible to frame 

 rules and tables of freeboard which would embodv the 

 results of safe loading, and prevent steamers being sent to 

 sea in a dangerously overladen condition. 



The present Board of Trade freeboard rules and tables, 

 which limit, by an .Act of Parliament passed in iRqo, the 

 depth of loading of British ships, were arrived at in this 

 manner. The first official tables were prepared in 1885 

 by a committee appointed bv Mr. Chamberlain when he 

 was President of the Board of Trade. 



The close attention paid during recent Years to the pro- 

 tection of openings in the weather-deck, in association with 

 the strict limitation of loading now enforced bv the Board 

 of 'n-ade freeboard tables, has resulted in an extraordinary 

 diminution of losses at sea. The effect upon safety of 

 Ihe present regulations, and of the improvement all round 

 in the size, strength, and equipment of ships is shown bv 

 the yearly statistics of losses, and it is well that the 

 figures relating to these should be known. In the three 

 calendar years 1881-3 there were iqSz of the British ships 

 registered in the United Kingdom, exclusive of fishing- 

 vessels, lost at sea from all causes — foundering, stranding, 

 collision, and missing — and 5^00 lives of crew in them] 

 besides -^32 passengers. For the three years ending June 

 30, iqo6, the corresponding figures were 654 ships, I3q4 

 lives of crew, and 133 passengers— and more than 100 of 

 these passengers were lost in the channel steamer Hildn, 

 on hrr p.assage to St. Malo in November, 1905. Ihe 

 number of lives of crew lost at sea has thus been reduced 

 to one-fourth of what it was twenty-five years ago, while 

 not more than thirty passengers, besides the unfortunate 

 victims of the Ilihla disaster, lost their lives in all the 

 vessels, large and small, that were lost at sea during the 

 three years ending June 30, 1906. 



.An important element of safety at sea is the division 

 of the hull into separate water-light compartments. A 

 NO. 1969, VOL. 76] 



collision with another ship may occur, and it is necessary 

 to provide, in such case, against being sent quickly to the 

 bottom. Much attention has been given to this point 

 during recent vears, especially in large passenger liners. 

 The number and positions of the water-tight bulkheads in 

 these are often regulated so as to carry out the recom- 

 mendations of the Board of Trade Bulkheads Committee, 

 presided over by the late .Sir E. J. Harland in iSqi. 



Compliance with the Bulkhead Committee's rules is 

 optional on Ihe part of shipowners, but, although they 

 may be .sometimes used as a guide in fixing the position 

 of bulkheads, full compliance with their requirements is 

 by no means general, even in the highest class of steamers. 



The next point of vital importance to safety at sea is 

 stability. The stability of a ship when floating in 

 equilibrium in still water is readily calculated, and is 

 represented graphically by curves which show at any angle 

 of inclination what the righting moment is which operates 

 to move her back towards the upright position supposing 

 her to have been forcibly inclined away from it. It is thus 

 determined very completely for the assumed still-water con- 

 ditions, but the designer, although he is obliged to trust 

 to his judgment for making it satisfactory for sea-going 

 purposes, often knows little of what it may become under 

 working conditions upon a voyage. I made two voyages 

 in a large ocean liner not long ago, the metacentric height 

 of which is about 7 inches when light and 18 inches when 

 filled up with passengers, stores, fresh water, coals, and 

 a homogeneous cargo of such density as completelv fills 

 all the cargo spaces and immerses her to her load draught. 

 The metacentric height was 2 feet 2 inches at sailing 

 upon the first voyage ; at the middle of the voyage it was 

 21 inches, and at Ihe end 20 inches. Upon the second 

 voyage the metacentric heights were 2 feet 10 inches at 

 starting, 16 inches in the middle of the voyage, and 

 20 inches at Ihe end. The irregularities in the metacentric 

 height from day to day were largely due to the manner 

 in which the water-ballast was used. This was the case 

 of an ocean liner, in which the weights carried were 

 about one-half the fixed weight of the hull and machinery. 

 In a large cargo-steamer, where Ihe weights carried mav 

 amount to twice Ihe weight of the hull and machinery, it 

 will be seen how much the stability on service depends 

 upon tho.se who regulate the loading, and how little upon 

 the designer. 



The ship-designer requires to decide, of course, what 

 metacentric height to give a ship in the circumstances to 

 which his calculations apply, but it is only by comparison 

 with other .ships of similar types that have been found 

 satisfactory after passing into the hands of their owners 

 that he can properly fix the exact figure. 



The question of stability was raised before the Loadlino 

 Committee of 1885 in connection with the regulation of free- 

 boards, and has often been revived since. It has been felt, 

 however, that stability is so intimately related to stowage, 

 and so much in the hands of those who regulate it, 

 that it would be impossible to treat stability satisfactorily 

 as a mere factor of depth of loading. Nothing can 

 make a ship safe if her stability is not secured by proper 

 stowage; but when vessels will obviously admit of being 

 loaded with homogeneous cargoes, so as to have their 

 stability dangerously reduced at sea, the oflicial bodies who 

 assign load-lines should look for proof that the danger is 

 understood, and that proper measures will be taken in 

 regulating the stowage to guard .against it. I understand 

 this is the course taken by the Board of Trade and the 

 authorities who assign freeboards when cases of such a 

 nature come before them. 



One of the most important elements of safety at sea is 

 structural strength, and there is no more intricate or 

 difficult problem which we have to consider. Mercantile 

 steamers have been made what thev are, in respect of 

 design and strength of structure, chiefly by observation and 

 experience of the effects of straining action at sea. The 

 usual calculations of strength of structures do not carry 

 us very far by themselves in shipbuilding, and although 

 much attention has been given to these by ship-designers 

 they cannot be greatly relied upon in practice. As a 

 matter of fact, Ihe arrangement of m.-iterial shown upon 

 the transverse section of a ship, and the sizes of the 

 various parts, are practically what they have been made 



