SELECTION OF THE BEST KIND OF PROPELLING MACHINERY. 233 
Let us take the author’s own figures, 11 tons for the Diesel-engine ship. I want to tell 
you that the Selandia and the Jutlandia have not burned over 9 tons per day. I am 
giving you the benefit of the doubt and charging the motor ship up with 11 tons. Eleven 
tons per day for thirty days means 330 tons, and adding 15 per cent, which is 49.50, amounts 
to 379.50 tons. If you subtract 379.50 from 1,173, you will get 793.5 tons in the double 
bottom which could be saved out of that ship to pay her expenses. Thus, taking the figure 
of $10 a ton cost for oil means you will have approximately $5 a ton on that transportation. 
In that case, $3,967.50 for what you sold, and the cost at $10 a ton for what you burn— 
you will remember that the cost is $3,795—you would be ahead almost $200, besides paying 
for all the oil you burn on the round trip, there and back. 
PROFESSOR CHARLES E. Lucke, Member (Communicated) :—The author is correct in 
saying that the answer to the question of whether Diesel or steam machinery will be better 
for any given vessel, and the answer that refers to any one type of either kind, is a matter 
that must be worked out by evaluating a large number of variables. While, of course, cer- 
tain general conclusions can be arrived at, the final solution must rest on detailed figures. It 
is true, as the author says, that if the voyage is long enough, or the sea days per year great 
enough, the motor ship will pay over the steam, but the question then arises as to how much 
is “enough.”” The real question, therefore, in this problem is one of method of treating these 
many variables so as to give clearly the answer sought. 
After many attempts to do this in tabular fashion, supplemented in some cases with 
curves, all were rejected finally in favor of a new mode of procedure, which seems to be 
satisfactory and has been used by many people since its publication. This method of treat- 
ment, which leads to the desired solution in a very clear fashion, was expounded in a paper 
presented by me before the Franklin Institute, Wednesday, April 20, 1921. This paper was 
printed in the Journal of the Institute, July-August, 1921, and is entitled “Internal Combus- 
tion Engines in Marine Service.” 
It is very likely from the text of the paper here under discussion that the author was 
not familiar with this method, and his attention is invited to it as a means of making more 
clear the relations between the variables that he discusses and as a means for reaching the 
final answer. 
It is pointed out in conclusion that numerical values for any one variable, such as num- 
ber of men in engine-room crew, price of fuel, freight rate, cost of engines, all of which vary 
from time to time, may be treated in the method that is demonstrated as real variable and 
not as fixed quantities. When tabular methods are used exclusively, these figures, when 
given a proper range for any one item, lead to so many answers that the tables obscure the 
issue. This is wholly eliminated by the curve method. 
Mr. AcKErsoN (Communicated) :—Mr. Bogert is quite correct in that some of the 
inner bottom capacity could be used for cargo space in the shorter voyages and is a point 
that should be thoroughly considered when deciding the question of type of machinery. 
The author is not familiar with Prof. Charles E. Lucke’s paper entitled “Internal Com- 
bustion Engines in Marine Service,” but it would appear from the short description given by 
Professor Lucke that his method of treating the subject is an excellent one. 
Mr. Smith in his criticism says that, on account of the cost being largely a function of 
weight, weight is second in importance to fuel consumption. In my paper I mentioned cost 
