HEAVY-OIL ENGINES FOR MARINE PROPULSION. 235 
a given weight per horse-power it permits of a reduction in piston speed, 
and, consequently, of a slower number of revolutions and of a larger and 
more efficient propeller. As it happens, the first large marine, double- 
acting engines have taken advantage of the latter in preference to the former 
feature. When applied to large ocean going steamers where the question of 
weight and space is not of paramount importance as compared to reliability, 
the builders of these recent engines appear to have been wise. Even with 
the comparative low piston speed and massive parts, there is a saving in 
weight and space as compared with the usual steam plant for the same 
class of vessel. It is interesting here to note that the owners of two of these 
large vessels have had occasion to complain of the small space occupied by 
the engine, slow and strong as it is, because of the rules for measurement 
for tonnage and consequent dues. ‘This, of course, is only a passing phase 
of the problem and is only another instance of the case where engineering 
developments are ahead of the laws and customs. 
THE MECHANICAL PROBLEMS CONNECTED WITH HEAVY-OIL ENGINES. 
In general the mechanical problems which have been met and solved 
in Diesel engines are of the same nature as those encountered in large gas 
engines. In fact, the firms which have done most to develop the oil engine 
have had a wide experience with gas engines, and utilized much of the knowl- 
edge thereby acquired, in their oil engine construction. 
The problem of dealing with heat in cylinders and pistons is dealt with 
as in gas engines. In large marine engines the latest tendency is to cool - 
the pistons by means of circulating oil in their heads. The heated oil on 
leaving the pistons is passed through a cooler, consisting of a nest of tubes 
around which cooling water is circulated. ‘The reason for using oil as a 
cooling medium instead of water is that slight leakages in the flexible con- 
nections is not objectionable, and would not interfere with the lubrication 
of working parts. Oil, however, is not as good a conductor as water, and 
also has a much smaller specific heat. 
Materials.—In the earlier types of Diesel engine the columns, bedplates, 
cylinders and water jackets were made of massive cast iron. ‘This insured 
ample strength and durability, but made the engines very heavy, some of 
them weighing as much as 400 pounds per horse-power. As these earlier 
engines were used on land only, there was and is no objection to their 
heavy construction. 
When the attention of marine engineers was directed toward heavy-oil 
engines, radical changes in construction were at once inaugurated to adapt 
