Manoeuvrability and Propulsion of Very Large Tankers 



• Model n, having an afterbody with extremely V-shaped sections and a 

 rudder shoe. 



• Model ni, having an afterbody with extremely U-shaped sections and a 

 rudder shoe. 



• Model rv, having a cigar-shaped stern (Hogner-type of afterbody) and a 

 Mariner rudder arrangement (clear-water stern). 



From the experimental investigations, it was concluded that model n, hav- 

 ing an afterbody with extremely V-shaped sections is to be recommended from 

 a viewpoint of resistance. The improvement in resistance qualities, however, 

 did not include a reduction of the required shaft horsepower. The reduction in 

 resistance is counterbalanced by a change in interaction effects between hull 

 and propeller. Investigations performed by Nichols et al. (6) have led to the 

 same result. Model I which is optimum according to the statistical data of the 

 N.S.M.B. is still optimum with respect to the delivered shaft horsepower at the 

 design speed of 16 knots. 



The cigar-shaped stern of model IV is bad from a viewpoint of resistance. 

 However, the interaction effects between hull and propeller are such that in the 

 loaded condition as well as in the light condition, model IV requires 2-3 percent 

 more power than the optimum hull form (model I). 



Measurements of the longitudinal component of the velocity in the plane of 

 the propeller were made with the four models. From these measurements it 

 was concluded that the circumferential inequalities behind model II is worse 

 than that behind the models I and in. Model IV shows the most homogeneous 

 wake pattern of all afterbody variations. 



Recently, the results of wake measurements made on a large number of 

 ship models at the David Taylor Model Basin have been published by Hadler and 

 Cheng (3). Both the longitudinal and the tangential velocity components of the 

 wake were measured. From experiments with a series of tanker models with 

 systematically varied stern shapes it was concluded that the models with the 

 more U-shaped stern tended to generate a more uniform longitudinal velocity 

 and a large downward velocity in the propeller plane near the propeller hub. 

 The more V-shaped stern tended to give a large fluctuation in the longitudinal 

 velocity, while the tangential velocity is relatively smaller in magnitude as is 

 the downward flow near the hub. From an analysis of the effect of the nonuni- 

 form velocity field on propeller cavitation and propeller-induced vibration, it 

 was concluded that the moderate U-shaped stern would provide best vibration 

 and cavitation characteristics. 



Wake measurements on a ship model with a Hogner-type stern have also 

 been presented by Hadler and Cheng (3). From a comparison of the results of 

 the Hogner-shape stern design and the conventional stern design from the 

 standpoint of minimizing vibration and cavitation problems in terms of uniform- 

 ity in flow, the superiority of the Hogner-type stern was evident. This conclu- 

 sion is in accordance with the results of observations of the cavitation patterns 



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