SELECTION OF THE BEST KIND OF PROPELLING MACHINERY. 
By J. L. Ackerrson, Esg., MEMBER. 
[Read at the thirtieth general meeting of the Society of Naval Architects and Marine Engineers, held in 
New York, November 8 and 9, 1922.] 
Never before has the marine engineering fraternity had so many different types of pro- 
pelling machinery to select from, and there is no empirical formula which can be applied to 
help select the best type. The problem of the shipowner in this respect is the most im- 
portant one he has today. Amongst the many factors to be considered in deciding what 
is the most suitable type are reliability (this is the most important single factor, for with- 
out reliability other advantages are very much discounted) ; economy in operation, initial 
cost, and weight, the relative importance of the last three depending on the type of ship under 
consideration. 
Numerous papers have been presented at these meetings, practically all of them having 
been prepared by the shipbuilder-—and they are thoroughly prepared, too; but there must be 
many factors that the shipowner is more familiar with than the shipbuilder, and it would be 
very interesting to hear from the shipowner his ideas on this matter. 
RELIABILITY. 
Reliability is something less tangible than the other three and responsibility less easily 
placed, because the factors controlling reliability emanate from two different sources: (1) the 
owner through the selecting of competent personnel; and (2) the builder. No matter how 
well a machine has been designed and constructed, if placed in the hands of an incompetent 
operator it will become unreliable; and vice versa, no matter how good the operating en- 
gineer, if the proper factors have not been used in the design and care in the construction, 
then the machinery is again unreliable; so that it is absolutely necessary for the operator to 
thoroughly understand and be whole-heartedly in support of any new design, and for the 
designer to realize that the cost of fuel per horse-power, while important, is not the only con- 
sideration. In the past five years we have had a very costly experience through sending to 
sea a large number of units (the design of which to begin with is questionable) in charge 
of engineers who were only half trained. 
ECONOMY. 
Economy in operation (that is, the fuel per horse-power) and initial cost usually bear 
a very close relation to each other, and it is only a question of figures to determine whether 
any particular type is worth the money as compared with any other type; and here again the 
type of vessel and the trade the vessel is employed in play an all-important part, as, for 
example, most tramp steamers over a cycle of, say seven years, are laid up for considerable 
periods at a time owing to there being no freight. During this lay-up the portion of expense 
due to fixed charges is going on all the time, while that portion consisting of fuel and supplies 
and operating personnel stops when the ship is laid up. 
