THE PKOGRESS IN STEAM NAVIGATION. 589 



tages over coal, reducing- greatly manual labor in embarkino- supplier 

 conveying it to the boilers, and using it as fuel. Possibly it'advocates 

 have claimed for it greater economical advantages over coal than can 

 be supported by the results of extended experiment. Even if tli.- 

 saving in weight for equal evaporation is put as low as 30 per roM of 

 the corresponding weight of coal, it would amount to 1,000 tons on a 

 first-class Atlantic liner. This saving might be utilized in greater 

 power and higher speed or in increased load. There would bc^i sub- 

 stantial saving on the stoke-hold staff. At present it does not appear 

 that adequate supplies of licjuid fuel are available. Competent authori- 

 ties here and abroad are giving attention to this (|uestion and to the 

 development of supplies. If the want can be met at prices justifyiiiu- 

 the use of liquid fuel, there will undoubtedly l)e a movement in that 

 direction. 



Stronger materials for the construction of hulls are alreadv avail- 

 able. They are, however, as yet but little used, except for special 

 classes of vessels. Mild steel has taken the place of iron, and effected 

 considerable savings of weight. Alloys of steel with nickel and other 

 metals are now made, which gives strength and rigidity much superior 

 to mild steel, in association with ample ductility. For destroyers and 

 torpedo boats this stronger material is no\\ largely usikI. It has also 

 been adopted for certain important parts of the structur(\s of recent 

 ships in the ro3'al navv. Of course, the stronger material is more 

 costly, but its use enables sensible economies of weight to be made. It 

 has been estimated, for example, that in an Atlantic linei- of -Jii knots 

 average speed about 1.000 tons could be saved by using nickel steel 

 instead of mild steel. This saving would suffice to raise the average 

 speed more than a knot, without varying the dimensions of the shij). 

 Allo3^s of aluminium have also been used for the hulls or portions 

 of the hulls of yachts, torpedo })oats, and small vessels. Consi(lei-abl(> 

 savings in weight have thus been effected. On the other hand, these 

 alloys have been seriously corroded when exposed to the action of 

 sea water, and on that account are not likely to be extensiveiv ummI. 

 Other alloys will proba])ly be found which will l)e free from tlii> 

 defect, and yet unite lightness with strength to a remarkable degree. 

 Other examples might be given of the fact that th«' metallurgist has 

 by no means exhausted his resources, and that the shijibuildei- may 

 look to him for continued help in the struggle to reduce the w.-ights 

 of floating structures. 



It is unnecessary to amplify what has already l>t't'ii said as to po>M- 

 ble increase in the efficiency and types of propellers. With limited 

 draft, as speeds increase and great powers have t«. I)i> utilized, 

 multiple propellers will probably come into use. Mr. Parsons has 

 shown how such problems mav be dealt with; and other mvestigators 

 have done valuable work in the same direction. In view of what has 



