580 THE PROGRESS IN STEAM NAVIGATION. 



extent. High steam pressures are used. The engines are run at a 

 high rate of revolution — often at 400 revolutions per minute. Great 

 care is taken in every detail to economize weight. Speed trials at 

 maximum power extend over only three hours. On such trials in a 

 destroyer each ton weight of propelling apparatus produces about 45 

 indicated horsepower. Some idea of the relative lightness of the 

 diestro3^er's machiner}' and boilers will be obtained when it is stated 

 that in a large modern cruiser with water-tube boilers, high steam 

 pressure, and quick-ruiming engines, the maxinuim power obtained 

 on an eight hours' trial corresponds to about 12 indicated horsepower 

 per ton of engines, boilers, etc. That is to say, the proportion of 

 power to weight of propelling apparatus is from three and a half to 

 four times as great in the destroyer as it is in the cruiser. 



(2) A very larg*' percentage of the total weight, or displacement, of 

 a torpedo vessel is assigned to pi"i)i)elling ap[)ai'atus. In a destroyer 

 of 80 knots trial speed, neaily one-half the total weight is devoted to 

 machinery, boilers, (^tc. In the swiftest cruist'rs of large size, the 

 corn»s])()n(ling allocation of weight is less than 20 per cent of the dis- 

 ])lacement. and in the largest and fastest mail steamers it is about 20 

 to 2;") per cent. 



(3) The torpedo vessel carries a relatively small load of fuel, ecjuip- 

 ment, etc. Taking a /50-knot destroyer, for example, the speed trials 

 are made with a load not exceeding 12 to 14 per cent of the dis])lace- 

 ment. In a swift cruiser the corresponding load would be from 40 

 to 45 per cent, or proportionately more than three times as gieat. 

 What this diflerence means may be illustrated by two statements. If 

 the load were trebled, and the vessels correspondingly increased in 

 draft and weight, the speed obtiiined with the same maximum power 

 would be about 3 knots less. If, on the other hand, the vessel 

 were designed to attain 30 knots on trial with the heavier load, her 

 displacement would i)robably be increased about 70 to 80 per cent. 



(4) The hull and fittings of the torpedo vessel are exceedingly light 

 in relation to the dimensions and engine power. For many parts of 

 the structure steel of a high tensile strength is used. Throughout 

 the utmost care is tiiken to economize weight. In small vessels, for 

 special service, many conditions can be accepted which would be inad- 

 missible in larger seagoing vessels. The result of all this care is the 

 production of hull structures having ample general strength, but very 

 little local strength; but notwithstanding all the accidents of naviga- 

 tion and collisions that have occurred in this class of vessels, and they 

 have not been few, not one has j'^et foundered at sea. 



These conditions are essential to the attainment of very high speeds 

 for short periods. They resemble the conditions ruling the design of 

 cross-channel steamers, so far as relative lightness of propelling appa- 

 ratus, small load, and light scantlings are concerned. The essential 



