McClure and Hove 



propellers with both ahead and astern rotation and ahead and astern velocity. 

 Self-propelled tests were conducted to determine propeller-hull interaction. 

 Aside from the greater than usual importance of knowledge of propeller thrust 

 at negative speeds, there is nothing particularly unusual in selection of the main 

 propeller characteristics. 



The shrouded steering propellers can be directed at any angle to the ves- 

 sel's center line. When correcting an adverse heading, the positioning unit will 

 frequently be directed at a large angle to the direction of motion. Performance 

 data for these conditions were not available in the literature, so it was neces- 

 sary to conduct tests with varying inflow angles. The propeller is a modified 

 Kaplan type with four blades similar to the van Manen K 4-55 series. The noz- 

 zle is a van Manen No. 18 modified by opening up the inlet to compensate for the 

 hub nacelle. The positioning unit propeller and nozzle are described more fully 

 in Appendix B. 



Tests in both open water and in the presence of a hull segment were con- 

 ducted at the University of Michigan Naval Tank using a 1:7.5 scale model. 

 Equations were fitted to the data (6) to complete the performance map and to 

 facilitate positioning analysis. 



Kj. = (0.50+ 0.45 Jg) COS 9 - ]^ 



Kg = (0.50+ 0.45 Jg) sin 6 



where 



Ja = advance coefficient 



6 = angle of propeller shaft to the flow. 



As defined here k^ is in the direction of flow and Kg is at right angles to it. 

 Figures 7, 8, and 9 are plots of the longitudinal force, side force, and torque 

 coefficients in open water. 



An additional factor affecting positioning unit performance is the proximity 

 of the hull. When the platform is moving ahead, only a slight frictional boundary 

 layer influences the propeller. An athwartship's velocity component around the 

 hull creates an accelerated region in the vicinity of the propeller. The effect of 

 the hull is equivalent to an increase in transverse velocity component of about 

 25 percent. 



For general application, Taggart (7) gave the following equations for 

 propeller-nozzle performance in open water as a function of pitch ratio. These 

 are based on the Mohole test data and tests by van Manen with the assumption 

 that pitch ratio effects measured in axial flow hold proportionately at other 

 angles. 



422 



