486 



NATURE 



{March 25, 1880 



" In fact, the figures themselves in the Table of Losses 

 show that there were as many coal-laden steamers as 

 grain-laden steamers lost during the months of the past 

 winter ; and although it is possible for coal to shift simi- 

 larlv to grain, it is not a cargo which is prone to shift, or 

 which would be considered dangerous in a fairly-designed 

 vessel. In view of these facts there is nothing to show 

 that the inherent deficiency of stability of the vessels, 

 loaded as they were, might not have been as aclive an 

 agent, if not a more active agent, in creating the disasters 

 we deplore, as the shifting of the cargo." 



It is pretty evident from the author's remarks that 

 many of the steamers at present employed in the grain- 

 carrying trade are ill-proportioned for this purpose ; 

 though their stability would be amply sufficient when 

 carrying heavy non-homogeneous cargoes properly stowed. 

 The remedy proposed for new vessels is greater beam 

 and a higher freeboard, combined with a depth of double 

 bottom just sufficient for the purposes of water ballast. 

 For existing steamers of a dangerous type, the only 

 remedy is judicious stowage. This may perhaps best be 

 effected by lessening the weight of cargo between decks, 

 and by bringing the vessel back to the load-line, by intro- 

 ducing a corresponding quantity of water ballast into the 

 tanks in the hold. The only inconvenience of this course 

 would be to sacrifice a small fraction of paying freight ; 

 a trifling consideration when compared to the greater 

 security to human life. 



The problem of designing these vessels so as to suit the 

 peculiarities of all kinds of cargoes is by no means easy. 

 The requirements of a vessel which has only to carry 

 heavy dead-weights stowed low, and one which carries a 

 homogeneous cargo, like grain or coal, with a high centre 

 of ravity, are very different; and when the same vessel 

 has at different times to carry each description of loading 

 it becomes necessary to effect a compromise between too 

 much stability in the first, and too little in the second 

 case. In such cases it is best to err on the side of too 

 much stability, and to correct this quality when heavy 

 dead-weight cargoes are carried by raising the weights as 



ossible. 

 Mr. John's paper "On Cellular Construction of Merchant 



is interesting, as describing a recent return to the 



system of longitudinal construction, first introduced by 



Mr. Scott Russell over thirty years ago, and carried out 



by him in numerous iron vessels, notably the Great 



and the Annette. Mr. Scott Russell first in- 



this system in order to supply a great want in the 



iron vessels of that day, viz., deficient longitudinal 



a. Since then, however, the longitudinal strength 



iiant ships has been amply provided for by the 

 introduction of solid keelsons, skin platings, and of iron 



The present reaction in favour of a longitudinal 



of construction is, as Mr. John is careful to inform 

 us, due not to the necessity for providing additional 



1, but to the opportunities which it gives of incor- 

 porating water ballast tanks into the structure of the 

 bottom of the vessel. The details of this paper, which is 

 one of great interest and importance to practical ship- 



, are of too technical a character to be put before 

 our readers. 



are few questions of more practical importance 

 to both shipbuilders and owners at the present time, than 

 the substitution of steel for iron in the construction of 



ships. The greater strength of the new material renders 

 lightened scantlings possible, and the weight thus saved 

 in a vessel's hull represents so much addition to its cargo- 

 carrying capacity. Mr. Denny's paper "On Steel in the 

 Shipbuilding Yard" is a most valuable record of his 

 firm's experience in the use of steel, and it will be a sub- 

 ject for sincere congratulation to all those who are 

 interested, that Mr. Denny has pronounced the new 

 material to be absolutely trustworthy in every respect, far 

 more so indeed than wrought iron. At present the most 

 vexed question in connection with the use of steel is, what 

 limits of tensional strength shall be allowed. If it be 

 wished materially to reduce the scantlings of vessels it is 

 clear that a material of much greater tensional strength 

 than ordinary wrought iron must be made use of. On 

 the other hand the milder and more trustworthy the steel 

 the lower is its strength in this respect, while very strong 

 steels are proverbially hard and brittle. The Admiralty 

 and the two great classification societies, viz., Lloyd's 

 and the Liverpool Underwriters' Registry, have each at 

 present different limits of tenacity. The Admiralty 

 require that the breaking strength shall be between 26 

 and 30 tons per square inch ; Lloyd's between 27 and 31 . 

 while the Liverpool Underwriters fix the limits between 

 28 and 32 tons. The question as to which of these pairs 

 of limits is* the best, was mooted both by Mr. Denny and 

 by Mr. West, the Chief Surveyor to the Liverpool Under- 

 writers, who followed Mr. Denny with a paper on " Steel 

 for Shipbuilding." Both speakers inclined to the higher 

 limits ; in fact Mr. West went so far as to propose a 

 minimum limit of 30 tons, and to have no maximum limit. 

 He considers that a maximum limit is unnecessary, 

 because the temper-bending tests in common use amply 

 demonstrate whether or no the steel possesses the 

 requisite ductility. 



On the other hand Dr. Siemens, under whose patents 

 most of the steel used in shipbuilding is manufactured, 

 spoke strongly during the discussion in favour of the 

 milder and more ductile material. His grounds for doing 

 so were that the extensibility and strength of each variety 

 of the material were the same up to strains of 15 tons per 

 square inch, and that this strain is a long way beyond 

 anything which the material would have to bear in 

 practice. 



There were only two papers of any importance bearing 

 on the subject of the Royal Navy. The first was by Mr. 

 Barnaby, and was a description of the Kelson class of 

 protected cruiser. There are two of this class in 

 existence at the present time, viz. the Nelson and the 

 Northampton, They were originally designed as im- 

 provemements on the Bellerophon and the Iron Duke, 

 and viewed from this point they embody many novel 

 features, constituting no doubt great improvements. 

 The protecting armour in the newer vessels is much 

 more partial than in the older ones, but where it is 

 applied the average thickness is 7 '28 inches as against 

 528, representing nearly double the protecting power. 

 Again, the coal-carrying capacity of the Aelson and her 

 sister-ship is 1, 200 tons, as against 645 tons for the 

 Bellerophon and 460 tons for the Iron Duke. This is a 

 most iaiportant improvement. In fact the two last- 

 named vessels with their small coal-carrying capacity 

 hardly deserve the name of cruisers at all. The armament 



