128 



NA TURE 



[June 7, 1906 



THE STABILITY OF SUBMARINES. 

 T^HE construction of submarines for the Royal 

 ■•• Navy began about five years ago. On March 

 31, twenty-five vessels of the class had been com- 

 pleted, fifteen were building, and twelve more were 

 projected in the Navy Estimates for 1906-7. France 

 at the same date had thirty-nine submarines com- 

 pleted, and fifty building or projected. Russia had 

 thirteen vessels completed and fifteen building. The 

 United States had eight vessels completed and four 

 building, while Congress has recently sanctioned a 

 special vote of 200,000/. for further 'work on sub- 

 marines. Germany, Italy, and Japan as yet have 

 done but little, but they are moving in the same 

 direction. .An .American engineer, Mr. Holland, has 

 exercised the greatest influence on recent submarine 

 design, having worked at the problem for thirty 

 years, and proved himself a worthy successor of his 

 fellow-countrymen Bushnell and Fulton, who were 

 pioneers in submarine construction in the closing years 

 of the eighteenth century and the commencement of 

 the nineteenth. The first five British submarines, 

 ordered in iqoo, were repetitions of a type designed 

 by Mr. Holland, tried and approved by the United 

 States Navy Department. Great developments have 

 taken place in later British submarines, lliose first 

 built had displacements of 120 tons, surface speeds 

 of eight to nine knots, and gasoline engines of 160 

 horse-power. Vessels now building have displace- 

 ments exceeding 300 tons, a surface speed of thirteen 

 knots, and gasoline engines of S50 horse-power. The 

 cost of the earlier vessels was about 35,000/. ; that of 

 the later vessels must be twice as great. Other 

 countries have taken similar action, and some are 

 building still larger vessels. 



British submarines are kepi continuously at work, 

 and this experience has yielded valuable information 

 leading to successive improvements. The vessels 

 chiefly used for experimental purposes up to date 

 belong to the "A" class— 200 tons in displacement 

 and ten knots surface speed. Vessels of this class 

 consequently have been most before the public. Their 

 active ernployment has not been free from accidents, 

 but, having regard to novelty of type and special 

 risks which unavoidably accompany the power of sub- 

 mergence, it is a matter for congratulation that these 

 accidents have not been more numerous and serious 

 in their consequences. Official inquiries have been 

 made into the causes of accidents, and reports have 

 been published. In the opinion of the writer these 

 proceedings showed a tendency to minimise risks 

 necessarily encountered in working submarines. He 

 consequently undertook a lengthy" series of calcula- 

 tions for typical submarines of different dimensions, 

 in order to ascertain their conditions of stability in 

 various conditions which occur on service. The re- 

 sults for one class are embodied in a paper presented 

 to the Royal Society on May 3, which paper contains 

 also the results of similar calculations made for a 

 cruiser of ordinary form. The distinctive conditions 

 of submarines were emphasised by comparing these 

 results, and the editor of N.atcrk has suggested that 

 an explanation in popular language of the principal 

 conclusions, based on the investigations, may be of 

 general interest. 



Submarines are generally "cigar-shaped," with 

 circular or nearly circular cross-.sections. This form 

 is adopted in order to provide, with a minimum ex- 

 penditure of weight, structural strength sufficient to 

 meet severe external fluid pressures which may come 

 upon the hulls if submarines sink to considerable 

 depths. Such depths are not reached intentionally, 

 but experience shows that thev may be attained acci- 

 dentally, and that very quickly. 



NO. 1910, VOL. 74] 



In ordinary vessels the freeboard is considerable, 

 and the sides are approximately vertical between the 

 lightest draught reached on service and the deepest 

 (load) draught ; consequently, within these limits of 

 draught, horizontal sections of the vessels coincident 

 with the water-surface — known as planes 0} flotation 

 — remain practically constant in form, area, and 

 moments of inertia. In cigar-shaped submarines, with 

 circular cross-sections, the freeboard is small, and the 

 lightest draught of water bears a large proportion to 

 the diameter of the largest circular cross-section. For 

 the typical submarine dealt with in the Royal Society 

 paper, the extreme breadth (diameter of largest cross- 

 section) is a little more than twelve feet, and the lightest 

 draught of water is about ten feet. The circular form 

 of cross-section involves rapid diminution in lengths, 

 breadths, areas, and moments of inertia of successive 

 planes of flotation as the draught of water is in- 

 creased from light to load. These changes are ac- 

 companied by rapid and considerable losses in the 

 stability, and the conditions differ radically from those 

 of ordinary ships. For the typical submarine the extreme 

 length is 150 feet, and breadth extreme 12.2 feet; but 

 the length of water-line at the lightest draught is only 

 94 feet, and breadth 8.2 feet. When the draught of 

 water is increased eighteen inches (by admitting 

 water-ballast) and the vessel is prepared for diving, the 

 length at the water-line falls to 41 feet, and the 

 breadth to 3.6 feet. In the cruiser of ordinary form 

 an equal change of draught produces small change 

 in length, bre.adlh, and area of the planes of flotation, 

 and these dimensions are practically equal to the ex- 

 treme length and breadth of the vessel. For the 

 cruiser the moments of inertia of successive planes of 

 flotation about their principal axes remain nearly 

 constant within these limits of variation in draught ; 

 whereas for the submarine moments of inertia 

 diminish rapidly as the draught of water is increased. 

 In the cruiser the extreme length is 260 feet, and the 

 metacentre for longitudinal inclinations is 352 feet 

 above the centre of buoyancy at light draught, and 

 328 feet when the draught is increased by eighteen 

 inches. In the submarine the extreme length is 

 150 feet, but the corresponding height of longitudinal 

 metacentre above centre of buoyancy is only 37 feet 

 at lightest draught, and falls to I5 feet when the 

 vessel is prepared for diving. At the lightest draught 

 the power of the submarine to resist longitudinal 

 inclinations (changes of trim) is relatively small ; in 

 the diving condition it is diminished almost to vanish- 

 ing point. It will be understood, therefore, that 

 when a submarine is prepared for diving every man 

 has to remain at his station, and no weights must 

 be moved; every opening into the interior must be 

 closed hermetically. The reserve of buoyancy is ex- 

 tremely small in the diving condition. A submarine of 

 more than 200 tons weight may have only 400 to 800 

 pounds reserve — representing 40 to 80 gallons of water. 



Even at their lightest draughts the reserve of 

 buoyancy of submarines is very small as compared 

 with that in other vessels. In good examples it is 

 6 per cent, of the corresponding displacement — little 

 more than half the lowest percentage accepted for 

 low-freeboard monitors when fully laden, and about 

 one-fourth the corresponding percentage for the 

 deepest laden cargo steamers. Openings into the in- 

 terior are placed at the tops of conning towers at a 

 considerable height above water, and .Admiralty 

 regulations provide that all openings shall be closed 

 before \\-ater-ballast is admitted to bring a vessel into 

 the diving condition. Further, it is now provided 

 that before proceeding at full speed at the surface, the 

 maximum reserve of buoyancy shall be secured by 

 emptying ballast tanks. One of the most serious acci- 



