138 SECTIONAL ADDRESSES. 
tonnage launched during 1930 the tankers constitute more than 30 per 
cent. of the whole output. About seven-eighths of these are motor- 
driven ; they carry oil and, naturally enough, consume it. Motor-driven 
tankers account for half the world-aggregate of motor tonnage launched 
in 1930. 
It is when we turn to vessels of intermediate types, to cargo liners and 
passenger liners which, though not of the largest class, are still notable 
ships, often catering for the luxurious traveller, that we find the liveliest 
contest between the steam turbine and the Diesel motor. And here one 
notes the curiously potent influence of nationality and of what may be 
called the accident of ownership. Some nations, such as Denmark, 
Norway and Sweden, conspicuously favour motors. Others, such as 
America, no less conspicuously favour steam. One feels that both 
cannot be right. Nor can British practice, which is much divided, be 
right either. The choice would sometimes seem to depend more upon the 
taste and fancy of some dominating personality than upon a careful 
weighing of arguments such as appeal to engineers. One finds some 
shipowning companies going strongly for Diesel engines and other com- 
panies going no less strongly for steam. A notable example in the steam 
group is the Canadian Pacific Company, whose superintending engineer, 
Mr. J. Johnson, has communicated to the Naval Architects a very full 
statement of the grounds which have governed that company’s engine 
policy. His paper deserves careful study ; I have not been able to find 
any equally detailed and convincing statement on the other side. 
A point which will be plain to any reader of Mr. Johnson’s paper is this, 
that to make a fair comparison of performance you must take both types 
at their certainly-attainable best. You must not compare modern Diesel 
engines with steam-engines of an antiquated type, but with turbines 
working under conditions that have been demonstrated to be practicable 
at sea, where high pressure and high temperature, with water-tube 
boilers, pure distilled water, no oil in the steam, and sound condenser 
tubes maintain an efficiency comparable with that which can be reached 
in the internal-combustion engine. It is right to recognise that the 
competition of the turbine with the Diesel engine has helped to develop 
on board ship an improvement in the efficiency of steam for which the way 
was already prepared by the experience of central stations ashore. Largely 
through the preaching and example of Parsons, we have learnt that the 
future of steam in marine propulsion depends on high pressure and high 
superheat. The experience of Mr. Johnson rubs this in. 
When we attempt to appraise the merits of the rivals and to estimate 
their chances in the more distant future, we see that from the thermo- 
dynamic point of view the Diesel engine still bas a small advantage. 
On the other hand, its oil is more costly than fuel oil for boilers, it must 
have lubricating oil, too, and the first cost of the engine is substantially 
greater than that of steam plant. In respect of weight and of space 
occupied there is not much to choose; when account is taken of all 
accessories there is, perhaps, a slight advantage on the side of steam. 
As to durability, I cannot speak ; so far as I know, there is still a dearth 
4*The Propulsion of Ships by Modern Steam Machinery.’ Trans. Inst. Nav. 
Arch., 1929. Vol. 71, p. 39. 
