52 THE DETERMINATION OF THE RESISTANCE OF SHIPS. 



In recent years marked reductions in the power necessary to drive a given 

 weight of ship and cargo at a given speed have been made ; the experimental tanks 

 are justly proud of the cuts they have been able to make in the power for models 

 submitted to them for test. They are the people best placed to keep in touch 

 with developments so far as smooth-water results are concerned and are now pro- 

 ducing tangible results for merchant ships of all types as well as for warships, both 

 here and abroad. , 



In 191 2 the author read a paper before the Society which pointed out several 

 instances of saving due to experimentation ; before and since then much has been 

 written and something has been done to keep down coal bills. At the Franklin 

 Institute, Philadelphia, in the same year,- I ventured to suggest that the saving in 

 coal made by the naval architect might well be handed back to him in part to pro- 

 vide extra subdivision and stability for passenger ships — by no means a bad reply 

 to the question of extra first cost of additional beam and bulkheads — so that the 

 passenger need never really know any material difference in the price of his ticket 

 due to increased first cost of ship. 



The efiforts connected with twin-screw drives for full-cargo ships, both steam 

 and motor driven, have recently shown some unusually good results. Recent col- 

 liers built for the navy are cases in point, and their trials and service results are 

 of particular value in all similar twin-screw vessel design, steam or motor. 



In recent years a strong tendency to conduct systematic experiments on ship 

 resistance is noticeable, and for this we cannot be too grateful. Isolated puUings 

 of models as submitted are necessary, but it is only when the lessons drawn from 

 these experiments are followed by systematic research that the profession as a whole 

 begins to derive benefit from the work done. We have passed from the stage of 

 individual and disconnected experiments to that of systematic research directed 

 along lines that are already having a marked eflFect in reducing power or increas- 

 ing speed in shipping generally. > 



It should also be remembered that model experiments are only half the battle; 

 they must be followed by a progressive trial on the measured mile in order that 

 the design of the propellers may be verified and the performance of the machin- 

 ery properly noted. This trial should be conducted at the same trim and draught 

 as the model was towed, and this should be as near the working load draught as 

 possible and deep enough to give proper immersion to the screws. It will not al- 

 ways be easy for the builders to arrange for the loading of the ship, except in 

 the case of oil tankers; but this can generally be managed at the expense of a few 

 hours' delay to one voyage after the vessel is in service, once the owners realize 

 the savings that are at stake. 



At the time (1910) of the publication of Admiral D. W. Taylor's manual the 

 literature of this subject was beginning to assume good proportions. It was, how- 

 ever, scattered, and the naval architect who did not keep in touch with a good many 

 sources of information was at a serious disadvantage. This book brought to- 

 gether the best collection and arrangement of experimental data that we have. The 



