STUDIES OF THE APPLICATION OF 



DUCTED AND CONTRAROTATING 



PROPELLERS ON MERCHANT SHIPS 



Hans Lindgren, C.-A. Johnsson and Gilbert Dyne 



The Swedish State Shipbuilding Experimental Tank (SSPA) 

 Goteborg, Sweden 



ABSTRACT ■ =^ ■•■-'■' ^'- '■'■'^ • 



The paper starts with a survey of the trends in the development of 

 modern merchant ships and how these trends have influenced propeller 

 loadings and propulsive characteristics. Earlier studies on the appli- 

 cation of ducted and contrarotating propellers are summarized and 

 some of the SSPA research activities in these fields are presented. 

 The SSPA design methods for ducted and contrarotating propellers are 

 outlined and some experimental verifications in uniform flow are dis- 

 cussed. Optimum propeller efficiencies, diameters and essential geo- 

 metric properties are given for different propeller loadings. 



Results of comparisons between conventional, ducted and contra- 

 rotating propellers applied to a 150 000 TDW tanker as well as conven- 

 tional and contrarotating propellers on a 12 000 TDW container vessel 

 project are reported. The comparisons are based on open-water and 

 self-propulsion tests as well as on cavitation tunnel tests in uniform 

 flow and irregular wake distributions. Some concluding remarks and a 

 scheme for further investigations are given at the end of the paper. 



1. INTRODUCTION 



The recent, explosive development of ship size, speed, and engine power 

 available for the powering of merchant ships, has been accompanied by in- 

 creased propulsion problems. Questions concerning efficiency, cavitation, and 

 vibration have become highly important. About 15 years ago there was a clear 

 trend towards single -screw propulsion with diesel engines of low number of 

 revs. The development during the last 10 years has caused increased interest 

 in very high engine powers and thus actualized multiple -engine arrangements 

 and, for large tankers, still lower number of revs. In this connection also, dif- 

 ferent, for merchant-ship propulsion, less conventional propeller arrangements 

 have been discussed. Below are presented the results of an investigation of the 

 application of conventional, ducted, and contrarotating propellers on merchant 

 ships, carried out at the Swedish State Shipbuilding Experimental Tank (SSPA). 



The development for tanker ships has been characterized primarily by in- 

 creased size, increased block coefficient, and diminishing length-draught ratio. 

 The speed has essentially remained unaltered. For dry cargo ships, the size 

 has not changed so radically, and the block coefficient has tended to decrease. 



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