CHAPTER 70 



Screw-Propeller Design 



70.1 General Considerations 582 70.25 



70 . 2 Design Requirements for a Screw Propeller . 583 70 . 26 



70.3 Comments on Available Design Methods 



and Procedures 583 70.27 



70.4 Requirements for, Availability of, and List- 



ing of Propeller-Series Charts 584 



70.5 Comments on and Comparison of Propeller- 



Series Charts 589 



70.6 Prehminary-Design Procedure, Employing 



Series Charts 592 



70.7 Modification of Series-Chart Procedure for 



Other Design Problems 596 



70.8 Preliminary Comments on Propeller-Design 



Features 596 



70 . 9 Selection of Propeller Diameter 597 



70.10 Determining the Rate of Rotation 597 



70.11 The Proper Pitch-Diameter Ratio; Pitch 



Variation with Radius 598 



70.12 Choice of Number of Blades 599 



70.13 Use of Raked Blades 600 



70.14 Propeller-Hub Diameter; Hub Fairing ... 601 



70.15 Determination of Expanded- Area Ratio; 



Choice of Blade Profile 602 



70.16 Selecting and Applying Skew-Back .... 603 



70.17 Design Considerations Governing Blade 



Width 605 



70.18 Selection of Type of Blade Section 605 



70.19 Shaping of Blade Edges and Root Fillets . . 606 



70.20 Partial Bibhography on Screw-Propeller 



Design 606 



70.21 Design of a Wake- Adapted Propeller by the 



Circulation Theory 609 



70 . 22 ABC Ship Propeller Designed by Lerbs' 1954 



Method 611 



70.23 Choice of the Number of Blades for the 



ABC Design 612 



70.24 Determination of Rake for the ABC Pro- 



peUer 612 70.46 



Propeller-Disc and Hub Diameters .... 612 



Calculating the Thrust-Load Factors and 

 the Advance Coefficients 613 



First Approximation of the Hj'drodynamic 

 Pitch Angle and the Radial Thrust Dis- 

 tribution 615 



Second Approximation of (3/ and the Radial 

 Thrust Distribution 616 



Determination of the Lift-Coefficient Product 

 and the Hydrodynamic Pitch-Diameter 

 Ratio 617 



Finding the Blade-Thickness Distribution . 620 



Blade-Section Shaping by Cavitation Cri- 

 teria 621 



Procedure When Cavitation is Not Involved 625 



Corrections for Flow Curvature and Viscous 

 Flow 625 



Final Blade-Section Shapes for the ABC 

 Design by Lerbs' Method 627 



Introducing Skew-Back in the ABC Blade 

 Profile 627 



Drawing the Propeller 629 



Calculating the Expected Propeller Efficiency 629 



Summary of Design Steps for Lerbs' Short 

 Method; Schoenherr's Combination . . 630 



Avoiding Air Leakage with Inadequate Sub- 

 mersion 631 



Design Comments on Propellers for the 

 Supereavitating Range 631 



Design of Bow Propellers, Coupled and Free- 

 Running 632 



Open- Water and Self-Propelled Model Tests 632 



Mechanical Construction; Type of Hub; 

 Shaping and Finish of Blades 633 



Blade Strength and Deformation 634 



Propeller Materials and Coatings to Resist 

 Erosion 635 



Prevention of Singing and Vibration .... 636 



70.1 General Considerations. The design of 

 screw propellers for ships, as developed at the 

 time of writing (1955), embodies so many facets 

 that nothing short of an entirely separate volume, 

 or book, can do it justice. Only in this way can 

 there be presented to the naval architect and 

 marine engineer all the useful and usable informa- 

 tion on this subject, including rules for propeller 

 design. G. S. Baker approached tliis two decades 

 ago [SD, 1933, Vol. II, pp. 1-68], and the Russians 

 made it a reahty in 1949, when they published 

 two comprehensive books on marine propulsion 

 and marine-propeller design. 



The design data and procedures are now so 

 numerous and so well laid down as almost to 

 justify the often-heard facetious remark: Design- 

 ing a good propeller is easy; one has to work only 

 to design a poor one. Nevertheless, cavitation at 

 low speeds, cavitation erosion, unbalance in 

 power between inboard and outboard screws, and 

 too large or too small propeller diameters still 

 turn up in the most unexpected places. Screw- 

 propeller design procedure, in all its phases, is by 

 no means adequate or perfected. 



Because of the large volume of existing litera- 

 ture, the discussion in this chapter carefully 



682 



