MECHANICAL AND USEFUL ARTS. 41 



3G0, viz., the vessel's assumed length, give 113,040 cubic feet, equal 

 to 3154 tons for each tubular bottom. The speed of the experimental 

 vessel is quite equal to the power, eight men constantly working her 

 by hand as fast before the engines were put in ; the screw which 

 works in undisturbed water ahead advances its length, viz., 4 feet, 

 during each turn or number of revolutions. — See Mechanics' Magazine 

 for further details. 



STRENGTH OF IRON SHIPS. 



Mr. John Grantham has read to the Institute of Naval Archi- 

 tects a paper upon this inquiry, which he concludes as follows : — 



The effect of experience in iron-ship building should be to remove 

 excessive weight in one part and add more weight to other parts, 

 until uniform strength is attained. At present the author's observa- 

 tion leads him to believe that signs of weakness are now most fre- 

 quently to be observed at the gunwale and sides amidships, and at 

 the hollow ends below the water-line. In the rules laid down by 

 Lloyd's Committee the strengthening of these parts had not been 

 duly provided for. The Royal Charter presented a remarkable 

 example of the defects alluded to, and the author quoted from his 

 published work on Iron-Ship Building a passage, bearing upon this 

 subject, which was written after he h I examined that vessel in the 

 graving dock some time ago. He then discussed the three following 

 questions, viz. : — 1. The form and proportions to which the use of 

 iron in shipbuilding tends ; 2. The important bearing which form 

 and proportion have upon strength ; 3. How these tendencies should 

 be dealt with in iron ships. The tendency which the employment 

 of iron in shipbuilding has given rise to is, to build vessels, especially 

 steamers, much longer and finer than they were before. The author 

 bad frequently examined one vessel, that has sailed round the world, 

 whose length is nine times her breadth. A much greater proportion 

 of length to breadth may be ultimately attained, especially in large 

 vessels. But the excess of weight over displacement at the ends will 

 increase in the same ratio unless precautions are taken to reduce the 

 weight there. It is clear, however, that a vessel should be so con- 

 structed, and, where possible, so loaded, that when in smooth water 

 the weight should as nearly as possible correspond with the displace- 

 ment of every portion. The same conditions will also obtain when 

 the circumstances of a ship taking the ground are considered. The 

 construction of the Royal Charter was then examined at length, and 

 her weakness attributed, not to badness of material, nor to inferiority 

 of workmanship, but solely to the defective prinicples upon which 

 she was designed. The author contended for a great diminution in 

 the weight of iron ships at their extremities ; and stated that 

 Lloyd's Rules operated injuriously by narrowing too much the 

 sphere of improvement. He also considered it inconsistent to 

 class iron ships for years, as was at present done. He further held 

 it important to bear in mind that the chief strain which a ship has 

 to sustain is similar to that which is required in an ordinary girder, 

 and that any serious departure from this principle will lead to errors 



