Camber Corrections for Wide-Bladed Propellers," B. W. McCormick. Heat Transfer 

 and Fluid Mechanics Institute, University of California, Los Angeles, 1952. 



3. "The Effects of a Finite Hub on the Optimum Propeller," B. W. McCormick. Journal 



of Aeronautical Sciences, September 1955. 



4. "A Study of the Minimum Pressure in a Trailing Vortex System," B. W. McCormick, 



Ph.D. Dissertation, The Pennsylvania State University, June, 1954. 



5. "A Study of Torpedo Propellers — Part I;." B. W. McCormick, J. J. Eisenhuth, J. E. Lynn. 



Ordnance Research Laboratory Report NOrd 16597-5, March 30, 1956. 



R. W. L. Gawn 



The development of theory to the stage that many propeller designers have been 

 encouraged to apply the methods to practice has really only materialised during the 

 last decade or so, although the basic circulation theory was propounded long ago. 

 This is not at all surprising, since detailed corrections are involved for blade width, 

 number of blades and other characteristics and it was necessary to establish these with 

 the degree of accuracy essential to the propeller designer. In fact no more than a few 

 years ago the induced velocities on the lifting line could only be reliably determined 

 for an optimum distribution of circulation. Dr. Lerbs extended this to an arbitrary 

 distribution and later evolved a method for determining the pitch corrections to take 

 account of lifting surface effect. Such details generally are more important for pro- 

 pellers with wide blades as the theory is then less accurate and progressively so with 

 increase of width. Dr. Lerbs' approach has been an invaluable guide in propeller 

 design at the Admiralty Experiment Works, Haslar, and this opportunity of paying 

 tribute to his admirable work is warmly welcomed. 



There are, of course, many major aspects of design that the theory of propulsion 

 does not cover. For example, full regard must be paid to strength, stiffness, manoeuvr- 

 ing qualities, propeller induced vibration and erosion, as well as propulsive efficiency 

 over the operational speed range of the ship. The propeller must be suited to the hull 

 and to the machinery. Many admirable researches have already been devoted to the 

 various aspects mentioned but there seems ample scope for further development of the 

 theory and it is suggested to Dr. Lerbs that among other important matters calling for 

 further elucidation are cavitation, distribution of pressure, the interaction between hull 

 and propeller and non axial flow to cover inclinations up to at least 15 degrees. 



The designer has for long years been fortified by charts showing the variation 

 of thrust, torque and efficiency of propellers over a wide range of slip obtained from 

 tests of a series of model propellers in which one or more basic parameters of design 

 have been systematically varied. One of the latest results of such tests published by 

 myself three years ago covered the full range of pitch ratio and blade area ratio of 

 practice. Each propeller was of constant pitch and segmental blade section which is a 

 type that has long been recognized as efficient. One contribution of theory is to indicate 

 the modifications that can be made to this comparatively simple shape with possible 

 advantage albeit small. Dr. Lerbs' theory has been of great help in modifying the 

 shape to suppress tip vortex or other type of cavitation to a higher speed and generally 

 the indications of theory have been confirmed by tests of the model so modified in a 

 Cavitation Tunnel. It frequently happens however that the propeller design so developed 

 requires some further adjustment, to suit the particular hull and machinery and this 

 is determined from the results of speed trials of a previous comparable type of ship. 

 The final propeller design is thus a blend of theory with model experiment and ship 

 trial results to which theory is making a contribution of increasing importance. 



For completeness propeller charts should cover variations of characteristics other 

 than the two mentioned above, namely pitch grading, blade section, camber, blade 

 outline, rake and skew. Some information on these variables has been published from 

 time to time but there is a need for a really systematic programme of tests. A com- 



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