ECONOMICAL CARGO SHIPS—SOME MODEL EXPERIMENTS. 53 
investigations on the distribution of displacement fore and aft, and this paper shows it 
does not necessarily follow that, by fining up a vessel, you can get one which will be more 
easily driven; in fact, if you examine the curves, you will find it is possible to add con- 
siderably to the displacement of a vessel, put the displacement in the right place, and 
get a vessel which will be more easily driven than one with less displacement. From an 
economical point of view, therefore, these results are very valuable. 
With regard to the differences between the tanks, at first it would appear as if there 
was a disagreement. We have tested at Ann Arbor a model, actually the same model 
pulled in the tank at Washington—it happened to be a model of a submarine—and the 
resistance curve checked almost absolutely, showing, so far as the results are concerned, 
the tanks are in agreement. | 
The difference enters in the allowance for surface friction, and that matter, as you 
know, has been discussed by Mr. Baker and by those on the other side, and is still perhaps 
somewhat open to doubt in comparing the model results with the full-sized ship. My 
own experience at Ann Arbor has been, in the results we have obtained and in checking 
them over with some vessels in actual service over a long period of time, that we get 
results which agree very well with practice. The Tideman’s coefficient of friction which 
we use seems to hit the case pretty closely. 
I may refer to one other fact which has been also the subject of a certain amount of 
controversy, and that is the shape of the sections of a ship, forward and aft. There seem 
still to be certain people who favor the club-footed section with straight sides, as against 
the section of the more V-shaped rounded form and flared-out side. I still have my own 
opinions in the matter as to which is the best form, particularly for full vessels; and in 
order to settle the matter we are conducting a series of experiments which, taken in con- 
junction with those which have been presented to us in the paper, will probably settle the 
question as to the most economical form of slow-going vessels for the future; that is, we 
are varying the shape of sections, keeping everything else constant. 
I would like to raise one point in the meeting today, and that is in connection 
with the method of presenting results. Mr. Robertson has chosen the Froude method, 
the C-constant value, and that has been open to a great deal of criticism, particularly 
from shipbuilders and naval architects who have to useit. If you are used to that method 
it is a comparatively simple thing; if you are not used to it, it causes a good deal of 
trouble, and I would like to have an expression of opinion from the members of this So- 
ciety as to what they consider the most desirable way of presenting results. One of the 
main purposes of a paper like this is to get the results before the shipbuilding fraternity 
and have them in such a form that the people interested will feel they can use them read- 
ily. If there are any suggestions to be made along that line, I think Mr. Robertson and 
I will be glad to hear them. 
Admiral Taylor and I adopted in the early days, if you will remember, the method 
of presenting results in the form of pounds per ton of displacement, and that seemed to 
us a rather simple method. The method of Froude, which Mr. Robertson has adopted, 
has certain advantages when you are used to it, but the thing is to get used to it. 
Mr. E. H. Rice, Member:—This paper by Mr. Robertson is, like his paper of last 
year, extremely interesting. Those of us who have been associated with the design of 
slow-speed ships for some years must have been recently struck by the fact that the field 
which was practically devoid of definite and valuable data for guidance, is now beginning 
