KENNETH R. REESOR THE SPEED AND POWER OF SHIPS A MANUAL OF MARINE PROPULSION BY D. W. TAYLOR, E.D., D. Sc., L.L.D. REAR ADMIRAL (C.C.)i U. S. N., RETIRED HONORARY VICE-PRESIDENT SOCIETY OF NAVAL ARCHITECTS AND MARINE ENGINEERS, MEMBER INSTITUTION OF NAVAL ARCHITECTS VOL. I. TEXT VOL. II. TABLES AND PLATES NEW YORK JOHN WILEY & SONS, INC. LONDON: CHAPMAN & HALL, LIMITED COPYRIGHT 1910 BY D. W. TAYLOR Entered at Stationers' Hall. London Stanhope fl>res F. H. OILSON COMPANY BOSTON. U.S. A 3-2* PREFACE THE intention of this work is to treat in a consistent and con- nected manner, for the use of students, the theory of resistance and propulsion of vessels and to give methods,, rules and formulae which may be applied in practice by those who have to deal with such matters. The contents are based largely upon model experiments, such as were initiated in England nearly half a century ago by Mr. William Froude and are now generally recognized as our most effec- tive means of investigation in the field of resistance and propulsion. At the same time care has been taken to point out the limitations of the model experiment method and the regions where it ceases to be a reliable guide. During the years that the author has directed the work of the U. S. Experimental Model Basin many results obtained there have been published in the Transactions of the Society of Naval Archi- tects and Marine Engineers and elsewhere, so, naturally, the experiments at the U. S. Model Basin have been made large use of wherever applicable. It will be found, however, that they are in substantial agreement with the many published results of the work of other experimental establishments of this kind. Although the coefficients and constants for practical application are mainly derived from the author's experience at the Model Basin and elsewhere, and are necessarily general in their nature, endeavor has been made wherever possible to develop formulae and methods in such a manner that naval architects and engineers derived using the book may, if they wish, adopt their own constants from their special experience. to For instance, by the methods given it will be found possible of a vessel the estimate closely the effective horse-power having form of what I have called the Standard Series, but it will also be to determine with fair accu- found possible, by the same methods, iii IV PREFACE racy the variation of resistance with changes of dimensions, etc., of vessels upon almost any lines for which a naval architect may have reliable data, and which, on account of satisfactory past results, or for other reasons, he may wish to use. The science of Naval Architecture is not yet developed to a point where our knowledge of resistance and propulsion is complete. While the author naturally hopes that this volume will at least partially bridge some of the gaps hitherto existing, much work remains to be done, and in a number of places attention is called to the need of further investigation of various questions. While we know something, for instance, in a qualitative way of the effect of shallow water upon resistance, information which would enable us to solve satisfactorily many problems arising in this connection is lacking, and apparently can be obtained only by much experi- mental investigation. When dealing with questions of wake and thrust deduction we are not yet upon firm ground, and it is to be hoped that the excellent work recently done by Luke in this con- nection will soon be supplemented by even more extensive investi- gations. D. W. TAYLOR WASHINGTON, D.C., July, 1910. CONTENTS CHAPTER I Preliminary and General SECTION PAGE 1. STREAM LINES i 2. TROCHOIDAL WATER WAVES 10 3. THE LAW OF COMPARISON 26 4. WETTED SURFACE 36 5. FOCAL DIAGRAMS 48 6. THE DISTURBANCE OF THE WATER BY A SHIP 50 CHAPTER II Resistance 7. KINDS OF RESISTANCE 57 8. SKIN RESISTANCE 58 9. EDDY RESISTANCE 66 10. WAVE RESISTANCE 73 11. AIR RESISTANCE 82 12. MODEL EXPERIMENT METHODS 87 13. FACTORS AFFECTING RESISTANCE 90 14. PRACTICAL COEFFICIENTS AND CONSTANTS FOR SHIP RESISTANCE 98 15. SQUAT AND CHANGE OF TRIM 108 16. SHALLOW WATER EFFECTS 112 17. ROUGH WATER EFFECTS 121 18. APPENDAGE RESISTANCE 123 CHAPTER III Propulsion 19. NOMENCLATURE, GEOMETRY AND DELINEATION OF PROPELLERS 128 20. THEORIES OF PROPELLER ACTION 136 21. LAW OF COMPARISON APPLIED TO PROPELLERS 150 22. IDEAL PROPELLER EFFICIENCY 153 23. MODEL EXPERIMENTS METHODS AND PLOTTING RESULTS 155 24. MODEL PROPELLER EXPERIMENTS ANALYSIS OF RESULTS 158 25. PROPELLER FEATURES INFLUENCING ACTION AND EFFICIENCY 166 26. PRACTICAL COEFFICIENTS AND CONSTANTS FOR FULL-SIZED PROPELLERS DERIVED FROM MODEL EXPERIMENTS 175 27. CAVITATION 182 v vi CONTENTS SECTION PAGE 28. WAKE FACTOR, THRUST DEDUCTION AND PROPELLER SUCTION 195 29. OBLIQUITY OF SHAFTS AND OF WATER FLOW 211 30. STRENGTH OF PROPELLER BLADES 216 31. DESIGN OF PROPELLERS 241 32. PADDLE PROPULSION 254 33. JET PROPULSION 260 CHAPTER IV Trials and Their Analysis 34. MEASURED COURSES 262 35. CONDUCT OF SPEED AND POWER TRIALS 264 36. ANALYSIS OF TRIAL RESULTS 279 CHAPTER V The Powering of Ships 37. POWERING METHODS BASED UPON SURFACE 291 38. THE EXTENDED LAW OF COMPARISON 295 39. STANDARD SERIES METHOD 300 CHAPTER I PRELIMINARY AND GENERAL i. Stream Lines 1. Assumptions Made. The consideration of stream lines or lines of flow will be restricted mainly to the case of the motion of liquid past a solid. It is sufficient for present purposes to define a liquid as a fluid which is incompressible, or virtually so, such as water. The difficulties in the way of adequate mathematical determi- nation of the motion of liquids past solids such as ships have hitherto been found insuperable. The mathematics of the motion of liquids is complicated; even the simple cases which can be dealt with mathematically require assumptions which are far from actual conditions in practice. Thus, when considering the motion of solids through a liquid, or what is the same thing mathematically, the motion of a liquid past solids, it is assumed that the liquid " " is perfect or has no viscosity and that the solid is frictionless, that is to say, that the liquid can act upon the solid only by pres- sure which must at each point be normal to the surface. In most cases that are dealt with mathematically, it is further assumed that the fluid or liquid extends to an infinite distance from the solid. 2. Steady Motion Formula. We cannot deal satisfactorily with problems of resistance by mathematical analysis, but in spite of the somewhat artificial assumptions involved, the results of mathe- matical analysis applied to a perfect liquid are of interest and value as they indicate tendencies and have large qualitative bearing upon the phenomena of the motion of water past ships. 2 SPEED AND POWER OF SHIPS One mathematical conclusion in this connection is particularly valuable. It is known as the steady motion formula and is as follows: = t+*+ z h . W 2g In the above formula, p denotes pressure of the liquid per unit area, w denotes weight per unit volume, v denotes velocity of flow in units of length per second, g acceleration due to gravity in units of length per second, z denotes height above a fixed level and h is a constant for each stream line, being called the head. It is usually convenient to express p in pounds per square foot, W in pounds per cubic foot, v and g in feet per second, z and h in feet. The above formula applies to the steady motion of an infinite mass of perfect liquid. For such liquid the value of h is constant for all particles passing a point fixed in the liquid. These particles form a continuous line called a stream line, and in steady motion, no matter how many twists and turns the stream line takes, the above formula applies to its pressure, velocity and elevation at every point. It will be observed that contrary to what might at first be thought, the greater the velocity at a point of the stream line the less the pressure, and vice versa. That is to say, if a stream of perfect liquid flows in a frictionless pipe of gently varying section, the pressure increases as the size of the pipe increases and decreases as the size of the pipe decreases. This is demonstrable in the case of flow through pipes, although it is necessary to have the changes of section very gradual in order to obtain the smooth continuous motion to which alone the steady motion formula is applicable. 3. Application of Steady Motion Formula to Ships. The steady motion formula applies to the motion of a liquid, including motion past a solid at rest. In the case of ships, we are interested in the motion of a solid through a liquid at rest. The two cases are, however, as already stated, mathematically interchangeable. Suppose we have a ship moving uniformly through still water which extends indefinitely ahead and astern. If we suppose both ship and water given the same velocity, equal and opposite to- the velocity of the ship in the still water we have the ship at rest and the water flowing past it. The mutual reactions between ship PRELIMINARY AND GENERAL 3 and water are identical whether we have the ship moving through still water or the water flowing past the fixed ship. To the latter case, however, the steady motion formula applies if we neglect friction and the mathematical treatment is much easier.