XASTS, IRON AND STEEL. As far back as 1838, the city of Dublin steam-packet coin pany had a steamer with hollow iron masts, the masts acting also as ventilating funnels for the cabins. From that time, iron has been frequently employed for lower masts. in sailing-ships as well as in steamers. The plan has usually been to make them of plates bent to the proper curvature, jointed by internal strips, and strengthened by an interna/ cross flange of plates secured by angle-irons; but sometimes the plates are lapped. The plates vary- from to I in. in thickness. .11r. Grantham that iron masts are 'lighter and stronger than timber masts; and when compared with ths. built-up masts of large vessels, are rather less expensive. For vessels of the same tonnage, the difference of weightis nearly two to three in favor of iron.
Iron is used for yards as well as masts. An iron yard was made in 1847 for the Australian clipper-ship Sch,omberg, 112 feet long, and varying in diameter from 14 to 2g in.; it weighed 71- tons. It was calculated that a timber yard of the same size would weigh 12i tons. Iron masts have since that time been employed in many ships in the royal navy, made of three vertical ranges of plates bent to the required curvature, with butt joints, and riveted to three T-irons which cover the joints on the inside.
Capt. Cowper Coles (drowned in the Captain, a martyr to his own inventiveness, 1870), the inventor of the turret system for ships of war, introduced tripod iron inasts. The real mast is strengthened and upheld by two others, the three forming a tripod. The
central tube, or real mast, is carried up to form the topmast; while the side tubes are carried up only to the height of the lower yard. The main tube rests upon the keelson; while the side tubes, which are on either side of it and behind it, rest upon parts of the bottom-framing; but all three are fa.stened to the deck as they pass through. The lower mast only fortes the tripod, and is self-supporting, without slirouds, etc.; the topmast is secured with stays, backstays, and out-riggers. Capt. Coles enumerated many advant ages which he believed this construction to possess.
Since the use of steel in shipbuilding has become recognized, the employment of the satne metal for masts has engaged attention: steel plates, we know, can now be made alniost as easily as plates of iron; and it becomes a question of increased efficiency against incre,ased cost ;is to which metal shall be adopted. Steel being a stronger metal than iron, masts of equal strength would weigh less if constructed of the former than of the latter metal. The hitherto not altogether unfounded distrust felt towards steel in the present state of its manufacture, has prevented its adoption from making such rapid progress as it was once thought it would. Actual use in war and in stormy weather will be nec essary, however to determine all the relative advantages of iron and steel for masts.
The subject of the stability of iron masts is treated with much fullness by Mr. Lamport, in a paper read before the Institute of Naval Architects in 1863.