Page 18 - Practical Ship Design

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Chapter 6 . Powering Z

6.1 An introduction to powering .......................... 1.55
6.2 Resistance and ship model correlation ..................... 156
6.2.1 The classical treatment of resistance .................. 1.56
6.2.2 The present day (ITTC’78) treatment of resistance .......... 157
6.2.3 Discussion of the two treatments .................... 158
6.2.4 Hull finish and the importance of skin friction resistance ....... 158
6.2.5 Ship-model correlation ........................ 160
6.2.6 Hull finish, AC and (I + x) ....................... 161
6.2.7 Steelwork roughness ......................... 162
6.3 An aide memoire on the components of powering ............... 162
6.4 Effective horsepower calculation methods in general ............. 171
6.5 Taylor’s method ................................ 172
6.6 Ayre’s C2 method ............................... 173
6.7 Moor’s method ................................. 174
6.7. I Single-screw ships ........................... 174
6.7.2 Twin-screw ships ........................... 175
6.8 Guldhammer and Harvald’s method ...................... 177
6.9 Holtrop and Mennen’s method ......................... 179

Chapter 7 . Powering ZZ

7.1 Power estimating using in-house data ..................... 187
7.1.1 The alternative methods ........................ 187
7.1.2 Re-analysis by an up-to-date method ................. 189
7.1.3 Calculating(1 +K) ........................... 194
7.1.4 The Grigson friction line ........................ 195
7.1 . 5 Corrections for differences in hull geometry .............. 198
7.2 Powering data ................................. 199
7.2.1 A “Ct” Method based on Moor’s and similar data ........... 199
7.2.2 Cln, for single screw ships ....................... 199
7.2.3 C,,,, for twin screw ships ........................ 204
7.2.4 C ,,,, for frigates, corvettes and high speed ferries ............ 204
7.2.5 Calculation of C, ............................ 205
7.2.6 Calculation of Pc ............................ 207
7.3 Appendage resistance ............................. 207
7.3.1 Most common appendages ....................... 207
7.3.2 Some approximate figures for appendage resistance .......... 208
7.4 Types of propulsors .............................. 209
7.4.1 General discussion ........................... 209
7.4.2 Single or twin screw .......................... 2 IO
7.4.3 Controllable pitch propellers ..................... 210
7.4.4 Highly skewed propellers ....................... 210