Introduction 



Taking for granted a knowledge of the material 

 in Volume I, a reader or user is enabled to lay 

 it aside temporarily and make the estimates or 

 calculations for the preliminary hydrodynamic 

 design of a ship, or the parts thereof, as well as 

 to carry through such a design, solely by reference 

 to Volume II. The latter is to be considered a 

 reference or design volume, containing little or no 

 theory or exposition and only sketchy descriptions 

 of the phenomena or physical laws involved. The 

 publication of these experimental and reference 

 data in a separate volume, in the shape of con- 

 tours, graphs, diagrams, tables, and other aids, 

 makes it possible to omit from Volume I much of 

 the strictly quantitative data which would have 

 interfered greatly with the continuity of its story. 



Many of the aspects of hydrodynamics as 

 applied to ship design have not yet been investi- 

 gated analytically, or else only the easiest and 

 simplest of the problems have been solved. In 

 these cases it is necessary to fall back upon 

 experimental results and empirical data. It must 

 be admitted that in some respects our knowledge 

 of naval architecture has not expanded greatly 

 from its position of nearly a century ago. At that 

 time the renowned hydrodynamicist, naval archi- 

 tect, and engineer, Wilham John Macquorn 

 Rankine, was moved to observe that: 



"Owing principally to the great antiquity of the art 

 of shipbuilding, and the immense number of practical 

 experiments of which it has been the subject, that part 

 of it which related to the forms of water-Unas has in many 

 cases attained a high degree of excellence through purely 

 empirical means. Excellence attained in that manner is 

 of an uncertain and unstable kind; for as it does not 

 spring from a knowledge of general principles, it can be 

 perpetuated by mere imitation only" ["On Plane Water- 

 Lines in Two Dimensions," Phil. Trans., Roy. Soc, 

 London, 1864, Vol. 154, p. 386]. 



Nevertheless, when necessity demanded, Ran- 

 kine himself was forced to fall back upon empirical 

 data, as is evidenced in his book "Shipbuilding: 

 Theoretical and Practical," published in 1866. 

 No apologies are therefore offered for following 

 this procedure in the present volume, especially 

 as, in every possible instance, an effort is made 

 to tie in these data with physical laws governing 

 the motion of liquids. 



Nor are any apologies offered for following J. 



Scott Russell, Rankine, and other contemporaries 

 in stretching to the utmost our existing knowledge 

 of hydrodynamics in its application to naval 

 architecture. They made incorrect assumptions 

 in some instances, and arrived at solutions which 

 later had to be corrected, but there is no doubt 

 that in doing so they advanced both the analytical 

 and applied phases of the art. 



A good measure of care is called for in the 

 application of data derived from past practice 

 and observations, in both ship operation and 

 model experiment. As Sydney W. Barnaby 

 observed in his book "Marine Propellers," written 

 in 1900, "No table can supply the place of judg- 

 ment and experience." By a generous insertion of 

 practical examples, in which the use of the form- 

 ulas, graphs, and procedures is illustrated in the 

 preliminary hydrodynamic design of a hypothet- 

 ical ship, embodied in Part 4, the reader may see 

 for himself what sort of answers and solutions are 

 derived. 



In general, all calculations in examples incor- 

 porated in this volume of the book are made with 

 English primary units of pounds, feet, and 

 seconds. Ship speeds may be given in knots in 

 the statement of the problem but are entered as 

 feet per second in the calculations. 



Wherever practicable, curves and graphs are 

 supplemented by simple diagrams illustrating the 

 coordinates or parameters. 



It is pointed out in the Introduction to Volume 

 I, and repeated here, that the formulas and 

 relationships used in this book for expressing 

 equalities, ratios, and the like are, with very 

 few stated exceptions, in what is known as pure 

 form. That is, they involve only physical con- 

 cepts and basic relationships between these 

 concepts. The units expressing them are kept 

 entirely separate, to be selected by the one using 

 the relationship. This procedure leaves no un- 

 certainty as to units, physical concepts, and other 

 factors which may be hidden in a mixed equation. 

 A case in point is the former use of 1.00 for 0.5p 

 in salt water, in the English pound-foot- second 

 system. The pure form also facilitates checking 

 for dimensionality because all physical quantities 

 stand out clearly. Furthermore, the relationships 

 are dimensionally consistent, so that equalities 



