Ship Design for Efficiency and Economy 2e pot

Ship Design for Efficiency and Economy Ship Design for Efficiency and Economy Second edition H. Schneekluth and V. Bertram Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2 8DP 225 Wildwood Avenue, Woburn, MA 01801-2041 A division of Reed Educational and Professional Publishing Ltd First published 1987 Second edition 1998  H. Schneekluth and V. Bertram 1998 All rights reserved. No part of this publication may be reproduced in any material form (including photocopying or storing in any medium by electronic means and whether or not transiently or incidentally to some other use of this publication) without the written permission of the copyright holder except in accordance with the provisions of the Copyright, Designs and Patents Act 1988 or under the terms of a licence issued by the Copyright Licensing Agency Ltd, 90 Tottenham Court Road, London, England W1P 9HE. Applications for the copyright holder’s written permission to reproduce any part of this publication should be addressed to the publishers British Library Cataloguing in Publication Data Schneekluth, H. (Herbert), 1921– Ship design for efficiency and economy.—2nd ed. 1. Naval architecture 2. Shipbuilding I. Title II. Bertram, V. 623.8 0 1 ISBN 0 7506 4133 9 Library of Congress Cataloging in Publication Data Shneekluth, H. (Herbert), 1921– Ship design for efficiency and economy/H. Schneekluth and V. Bertram. —2nd ed. p. cm. Includes bibliographical references and index. ISBN 0 7506 4133 9 1. Naval architecture. I. Bertram, V. II. Title. VM770.S33 98–20741 CIP ISBN 0 7506 4133 9 Typeset by Laser Words, Madras, India Printed in Great Britain by Contents Preface vii Chapter 1 MAIN DIMENSIONS AND MAIN RATIOS 1.1 The ship’s length 2 1.2 Ship’s width and stability 5 1.3 Depth, draught and freeboard 13 1.4 Block coefficient and prismatic coefficient 24 1.5 Midship section area coefficient and midship section design 27 1.6 Waterplane area coefficient 31 1.7 The design equation 33 1.8 References 33 Chapter 2 LINES DESIGN 2.1 Statement of the problem 34 2.2 Shape of sectional area curve 35 2.3 Bow and forward section forms 37 2.4 Bulbous bow 42 2.5 Stern forms 52 2.6 Conventional propeller arrangement 60 2.7 Problems of design in broad, shallow-draught ships 61 2.8 Propeller clearances 63 2.9 The conventional method of lines design 66 2.10 Lines design using distortion of existing forms 68 2.11 Computational fluid dynamics for hull design 79 2.12 References 83 Chapter 3 OPTIMIZATION IN DESIGN 3.1 Introduction to methodology of optimization 85 3.2 Scope of application in ship design 89 3.3 Economic basics for optimization 91 3.4 Discussion of some important parameters 98 3.5 Special cases of optimization 103 3.6 Developments of the 1980s and 1990s 106 3.7 References 110 Chapter 4 SOME UNCONVENTIONAL PROPULSION ARRANGEMENTS 4.1 Rudder propeller 112 4.2 Overlapping propellers 112 4.3 Contra-rotating propellers 114 4.4 Controllable-pitch propellers 115 4.5 Kort nozzles 115 4.6 Further devices to improve propulsion 132 4.7 References 147 Chapter 5 COMPUTATION OF WEIGHTS AND CENTRES OF MASS 5.1 Steel weight 151 5.2 Weight of ‘equipment and outfit’ (E&O) 166 5.3 Weight of engine plant 173 5.4 Weight margin 178 5.5 References 178 Chapter 6 SHIP PROPULSION 6.1 Interaction between ship and propeller 180 6.2 Power prognosis using the admiralty formula 184 6.3 Ship resistance under trial conditions 185 6.4 Additional resistance under service conditions 200 6.5 References 204 APPENDIX A.1 Stability regulations 206 References 213 Nomenclature 214 Index 218 Preface This book, like its predecessors, is based on Schneekluth’s lectures at the Aachen University of Technology. The book is intended to support lectures on ship design, but also to serve as a reference book for ship designers throughout their careers. The book assumes basic knowledge of line drawing and conven- tional design, hydrostatics and hydrodynamics. The previous edition has been modernized, reorganizing the material on weight estimation and adding a chapter on power prognosis. Some outdated material or material of secondary relevance to ship design has been omitted. The bibliography is still predominantly German for two reasons: ž German literature is not well-known internationally and we would like to introduce some of the good work of our compatriots. ž Due to their limited availability, many German works may provide infor- mation which is new to the international community. Many colleagues have supported this work either by supplying data, references, and programs, or by proofreading and discussing. We are in this respect grateful to Walter Abicht, Werner Blendermann, J ¨ urgen Isensee, Frank Josten, Hans-J ¨ org Petershagen, Heinrich S ¨ oding, Mark Wobig (all TU Hamburg-Harburg), Norbert von der Stein (Schneekluth Hydrodynamik), Thorsten Grenz (Hapag-Lloyd, Hamburg), Uwe Hollenbach (Ship Design & Consult, Hamburg), and Gerhard Jensen (HSVA, Hamburg). Despite all our efforts to avoid mistakes in formulas and statements, readers may still come across points that they would like to see corrected in the next edition, sometimes simply because of new developments in technology and changes to regulations. In such cases, we would appreciate readers contacting us with their suggestions. This book is dedicated to Professor Dr Ing. Kurt Wendel in great admiration of his innumerable contributions to the field of ship design in Germany. H. Schneekluth and V. Bertram 1 Main dimensions and main ratios The main dimensions decide many of the ship’s characteristics, e.g. stability, hold capacity, power requirements, and even economic efficiency. Therefore determining the main dimensions and ratios forms a particularly important phase in the overall design. The length L, width B, draught T,depthD, free- board F, and block coefficient C B should be determined first. The dimensions of a ship should be co-ordinated such that the ship satisfies the design conditions. However, the ship should not be larger than necessary. The characteristics desired by the shipping company can usually be achieved with various combinations of dimensions. This choice allows an economic optimum to be obtained whilst meeting company requirements. An iterative procedure is needed when determining the main dimensions and ratios. The following sequence is appropriate for cargo ships: 1. Estimate the weight of the loaded ship. The first approximation to the weight for cargo ships uses a typical deadweight:displacement ratio for the ship type and size. 2. Choose the length between perpendiculars using the criteria in Section 1.1. 3. Establish the block coefficient. 4. Determine the width, draught, and depth collectively. The criteria for selecting the main dimensions are dealt with extensively in subsequent chapters. At this stage, only the principal factors influencing these dimensions will be given. The length is determined as a function of displacement, speed and, if neces- sary, of number of days at sea per annum and other factors affecting economic efficiency. The block coefficient is determined as a function of the Froude number and those factors influencing the length. Width, draught and depth should be related such that the following require- ments are satisfied: 1. Spatial requirements. 2. Stability. 3. Statutory freeboard. 4. Reserve buoyancy, if stipulated. 1 2 Ship Design for Efficiency and Economy The main dimensions are often restricted by the size of locks, canals, slip- ways and bridges. The most common restriction is water depth, which always affects inland vessels and large ocean-going ships. Table 1.1 gives maximum dimensions for ships passing through certain canals. Table 1.1 Main dimensions for ships in certain canals Canal L max (m) B max (m) T max (m) Panama Canal 289.5 32.30 12.04 Kiel Canal 315 40 9.5 St Lawrence Seaway 222 23 7.6 Suez Canal 18.29 1.1 The ship’s length The desired technical characteristics can be achieved with ships of greatly differing lengths. Optimization procedures as presented in Chapter 3 may assist in determining the length (and consequently all other dimensions) according to some prescribed criterion, e.g. lowest production costs, highest yield, etc. For the moment, it suffices to say that increasing the length of a conventional ship (while retaining volume and fullness) increases the hull steel weight and decreases the required power. A number of other characteristics will also be changed. Usually, the length is determined from similar ships or from formulae and diagrams (derived from a database of similar ships). The resulting length then provides the basis for finding the other main dimensions. Such a conventional ship form may be used as a starting point for a formal optimization procedure. Before determining the length through a detailed specific economic calculation, the following available methods should be considered: 1. Formulae derived from economic efficiency calculations (Schneekluth’s formula). 2. Formulae and diagrams based on the statistics of built ships. 3. Control procedures which limit, rather than determine, the length. 1. Schneekluth’s formula Based on the statistics of optimization results according to economic criteria, the ‘length involving the lowest production costs’ can be roughly approxi- mated by: L pp D  0.3 Ð V 0.3 Ð 3.2 Ð C B C 0.5 0.145/F n  C 0.5 where: L pp D length between perpendiculars [m]  D displacement [t] V D speed (kn) F n D V/ p g Ð L = Froude number The formula is applicable for ships with  ½ 1000 t and 0.16 Ä F n Ä 0.32. Main dimensions and main ratios 3 The adopted dependence of the optimum ship’s length on C B has often been neglected in the literature, but is increasingly important for ships with small C B . L pp can be increased if one of the following conditions applies: 1. Draught and/or width are limited. 2. No bulbous bow. 3. Large ratio of underdeck volume to displacement. Statistics from ships built in recent years show a tendency towards lower L pp than given by the formula above. Ships which are optimized for yield are around 10% longer than those optimized for lowest production costs. 2. Formulae and diagrams based on statistics of built ships 1. Ship’s length recommended by Ayre: L r 1/3 D 3.33 C1.67 V p L 2. Ship’s length recommended by Posdunine, corrected using statistics of the Wageningen towing tank: L D C  V V C 2  2 r 1/3 C D 7.25 for freighters with trial speed of V D 15.5–18.5kn. In both formulae, L is in m, V in kn and r in m 3 . 3. V ¨ olker’s (1974) statistics L r 1/3 D 3.5 C4.5 V q gr 1/3 V in m/s. This formula applies to dry cargo ships and containerships. For reefers, the value L/r 1/3 is lower by 0.5; for coasters and trawlers by 1.5. The coefficients in these formulae may be adjusted for modern reference ships. This is customary design practice. However, it is difficult to know from these formulae, which are based on statistical data, whether the lengths determined for earlier ships were really optimum or merely appropriate or whether previous optimum lengths are still optimum as technology and economy may have changed. Table 1.2 Length L pp [m] according to Ayre, Posdunine and Schneekluth Schneekluth r [t] V [kn] Ayre Posdunine C B D 0.145/F n C B D 1.06  1.68F n 1 000 10 55 50 51 53 1 000 13 61 54 55 59 10 000 16 124 123 117 123 10 000 21 136 130 127 136 100 000 17 239 269 236 250 4 Ship Design for Efficiency and Economy In all the formulae, the length between perpendiculars is used unless stated otherwise. Moreover, all the formulae are applicable primarily to ships without bulbous bows. A bulbous bow can be considered, to a first approximation, by taking L as L pp C 75% of the length of the bulb beyond the forward perpen- dicular, Table 1.2. The factor 7.25 was used for the Posdunine formula. No draught limita- tions, which invariably occur for  ½ 100 000t, were taken into account in Schneekluth’s formulae. 3. Usual checking methods The following methods of checking the length are widely used: 1. Checking the length using external factors: the length is often restricted by the slipway, building docks, locks or harbours. 2. Checking the interference of bow and stern wave systems according to the Froude number. Unfavourable Froude numbers with mutual reinforcement between bow and stern wave systems should be avoided. Favourable Froude numbers feature odd numbers for the ratio of wave-making length L 0 to half- wave length /2 showing a hollow in the curves of the wave resistance coefficients, Table 1.3. The wave-making length L 0 is roughly the length of the waterline, increased slightly by the boundary layer effect. Table 1.3 Summary of interference ratios F n R F /R T (%) L 0 :/2 Normal for ship’s type 0.19 70 Hollow 9 Medium-sized tankers 0.23 60 Hump 6 0.25 60 Hollow 5 Dry cargo ship 0.29–0.31 50 Hump 4 Fishing vessel 0.33–0.36 40 Hollow 3 Reefer 0.40 2 0.50 30–35 Hump 1.28 Destroyer 0.563 1 Wave breaking complicates this simplified consideration. At Froude numbers around 0.25 usually considerable wave breaking starts, making this Froude number in reality often unfavourable despite theoretically favourable interference. The regions 0.25 <F n <0.27 and 0.37 <F n <0.5 should be avoided, Jensen (1994). It is difficult to alter an unfavourable Froude number to a favourable one, but the following methods can be applied to reduce the negative interference effects: 1. Altering the length To move from an unfavourable to a favourable range, the ship’s length would have to be varied by about half a wavelength. Normally a distor- tion of this kind is neither compatible with the required characteristics nor economically justifiable. The required engine output decreases when the ship is lengthened, for constant displacement and speed, Fig. 1.1. The Froude number merely gives this curve gentle humps and hollows. 2. Altering the hull form One way of minimizing, though not totally avoiding, unfavourable inter- ferences is to alter the lines of the hull form design while maintaining [...]... Recommendations for the choice of CB normally draw on the statistics of built ships and are usually based on the form CB D K1 K2 Fn (Alexander 26 Ship Design for Efficiency and Economy formula); one due to Ayre is 1.68Fn CB D C C D 1.08 for single-screw and C D 1.09 for twin-screw ships Today, often C D 1.06 is used The results of optimization calculations provided the basis for our formulae below These... the formula can be made more precise by setting C D CWP,A /CWP,N 2 where CWP,A is the actual and CWP,N the normal waterplane area coefficient For ships with pronounced V sections, such as trawlers or coasters, C D 1.1–1.2 For a barge with a parallel-epiped form, this formula produces for B/T D 2 an error KM D 1.6%, and for B/T D 10 an error KM D C4.16% 12 Ship Design for Efficiency and Economy The formula... containerships, the size and shape of the midship section are often adapted where possible to facilitate container stowage This may be acceptable for width and depth, but is not a good policy for CM , since this would affect only a few containers on each side of the ship 28 Ship Design for Efficiency and Economy 4 Effects on roll-damping Due to the smaller rolling resistance of the ship s body and the... Ð B Ð T Figure 1.20 Older and more recent midship section forms 30 Ship Design for Efficiency and Economy CM D 1 R2 2.33 Ð B Ð T Flared side-walls in the midships area Cargo ships usually have vertical sides in the midship section area Today, however, some are built with trapezoidal flared sides The ‘trapeze form’ (Fig 1.21) is more suitable than vertical sides in containerships because it improves the... dependent on many factors such as type, size and arrangement of superstructure and sheer The physical 24 Ship Design for Efficiency and Economy Figure 1.14 Table freeboards type B relationships between the data entered into the calculation and their effects on ship safety are not as clear as they appear in the calculation 3 Requiring subdivision and damage stability for larger tankers in the new freeboard... Type B: For Ebridge < 0.2L, linear interpolation between values of lines I and II For Eforecastle < 0.4L, line II applies For Eforecastle < 0.07L, the factor in Table 1.5b is reduced by 0.05 0.07L f / 0.07L , where f is the effective length of the forecastle 22 Ship Design for Efficiency and Economy Table 1.5b Correction Factor for superstructures E/L D 0 0.1 0.2 0 0.07 Type A 0.14 0.3 0.4 0.21 0.31... with trapezoidal midship sections and constant midship section areas reach the maximum Panama Canal width of B D 32.24 m before conventional ships with vertical sides 2 Same midship section dimensions—Thus the ship with a trapezoidal midship section has a smaller midship section area, the same CB and a higher CP The ship with trapezoidal midship section normally has higher resistance and power requirements... both the desired underdeck volume and hold space Section 3.4 includes approximate formulae for the underdeck volume 14 Ship Design for Efficiency and Economy 3 The position of the centre of gravity, KG, dependent on depth, can be verified using approximate methods or similar ships Following this, the chosen value of the metacentric height GM D KM KG can be checked For design purposes, an idealized depth... weight calculation Approximate formulae for KB and BM can be expressed as functions of the main dimensions, since a more precise definition of the ship s form has yet to be made at this early stage The main dimensions CB , L, B, T and D are determined first The midship section area CM , although not fixed in the early design stages, can vary only slightly for normal ship forms and is taken as a function of... the formulae These formulae show that in relation to the resistance, CB and L/B mutually influence each other A ship with relatively large CB can still be considered to be fine for a large L/B ratio (Table 1.6) The Schneekluth formulae (lower two lines of Table 1.6) yield smaller CB than Ayre’s formulae (upper two lines), particularly for high Froude numbers For ships with trapezoidal midship section forms, . Ship Design for Efficiency and Economy Ship Design for Efficiency and Economy Second edition H. Schneekluth and V. Bertram Butterworth-Heinemann Linacre House, Jordan Hill, Oxford OX2. D 1.1–1.2. For a barge with a parallel-epiped form, this formula produces for B/T D 2 an error KM D1.6%, and for B/T D 10 an error KM DC4.16%. 12 Ship Design for Efficiency and Economy The formula. 250 4 Ship Design for Efficiency and Economy In all the formulae, the length between perpendiculars is used unless stated otherwise. Moreover, all the formulae are applicable primarily to ships