CHAPTER 52 



Analysis of Flow Diagrams and Prediction of 

 Ship Flow Patterns 



52.1 Scope of Chapter 239 



52.2 Typical Ship- Wave Profiles 239 



52.3 Wave Profiles Alongside Models 241 



52.4 General Rules for Wave Interference Along- 



side a Ship 243 



52.5 Estimate of Bow-Wave and Stern- Wave 



Heights and Positions 244 



52.6 Prediction of the Surface- Wave Profile . . 246 



52.7 Typical Lines-of-Flow Diagrams for Ship 



Models 248 



52.8 Analysis of Model Surface-Flow Diagrams . 250 



52.9 Observation and Interpretation of Off-the- 



Surface Flow Data on Models 254 



52.10 Estimating the Ship Flow Pattern on the 



Body Plan 255 



52.11 Prediction of the Ship Flow Pattern at the 



Bilges 255 



52.12 Probable Flow at a Distance From the Ship 



Surface 256 



52.13 Estimating the Change in Flow Pattern for 



Light or Ballast Conditions 256 



52 . 14 Predicting Velocity and Pressure Distribu- 

 tion Around Ship Forms 257 



52.15 Use of Flow Diagrams for Positioning 



Appendages 258 



52.16 Estimated Flow at Propulsion-Device Posi- 



tions 258 



52.17 Analysis of the Observed Flow at a Screw- 



Propeller Position 259 



52.18 Flow Abaft a Screw Propeller 259 



52.19 Persistence of Wake Behind a Ship .... 261 



52.20 Bibliography on Wake 262 



52.1 Scope of Chapter. Supplementing the 

 potential-flow, ideal-liquid data on streamline 

 patterns around bodies and the discussion on 

 distribution of velocity and pressure in Chap. 42, 

 there is given here some representative informa- 

 tion on flow and on velocity-and-pressure distri- 

 bution in the water around ship models. There 

 are very few full-scale data on ships, either in the 

 technical literature or in form available for publi- 

 cation, with which to confirm the model data. 



Space limitations prevent the inclusion of the 

 vast amount of model data available in America, 

 mostly at the David Taylor Model Basin, on the 

 flow around ship models, representing many ship 

 types. Indeed, these data comprise sufficient 

 material for an entirely separate study and analy- 

 sis. 



52.2 Typical Ship- Wave Profiles. An analysis 

 of the flow patterns around a body or ship, at 

 least for a craft running on the surface, begins 

 properly with the surface-wave profile. This is the 



outstanding feature of the 3-diml flow around a 

 2-diml simple ship form, when the latter is 

 brought up from a deeply submerged position 

 and run at the air-water interface. This feature 

 has perhaps more importance for 3-diml forms 

 and actual ships because, at the speeds where 

 surface wavemaking is prominent, the wave 

 pattern there influences the flow over a consider- 

 able extent of the ship's side, often down to and 

 including the bilge-keel positions. 



Fortunately, it is not too difficult to obtain 

 the wave profile on a ship because this region is 

 available for observation or photographic record- 

 ing. A number of ships in the past have had 

 painted on one side a grid pattern of some sort 

 for the builder's or the acceptance trials. By 

 looking over the side, the intersections of the 

 actual wave profile could be observed and marked 

 on an outboard-profile drawing carrying the same 

 grid. The two full-scale profiles of Fig. 52.A, 

 for the U. S. battleship Maine (new), were ob- 



FiG. 52.A Observed Wave PROPitEs at Two Speeds on a BATiiiESHip 

 239 



