VARIATIONS OF SHAFT HORSE-POWER, PROPELLER REVOLU- 

 TIONS, AND PROPULSIVE COEFFICIENT WITH LONGITUDINAL 

 POSITION OF THE PARALLEL MIDDLE BODY IN A SINGLE- 

 SCREW CARGO SHIP. 



By Naval Constructor William McEntee, U. S. N., Member. 



[Read at the twenty-sixth general meeting of the Society of Naval Architects and Marine Engineers, held in 



Philadelphia, November 14 and IS, 1918.] 



Previous experiments made at the U. S. Experimental Model Basin indicate* 

 that for slow ships of full lines, such as are used for the ordinary single-screvi^ cargo 

 ship, it is desirable to use a certain amount of parallel middle body. In those ex- 

 periments the different models used had varying lengths of parallel middle body dis- 

 tributed equally forv^^ard and abaft the midship section. The present investigation 

 had for its object the determination of the best fore and aft position for the parallel 

 part of the ship, and the investigation of the effect of this variation on the shaft 

 horse-pow^er, propulsive coefficient, and wake and thrust deduction factors. 



Four 20-foot models were made corresponding to ships of 400 feet length be- 

 tween perpendiculars and of 57.3 feet beam, 26 feet draught, and 13,137 tons dis- 

 placement when fully loaded. A longitudinal or prismatic coefficient of 0.788 was 

 chosen as representing about the present practice in cargo carriers of this type. A 

 constant length of the parallel middle body was taken equal to 33 per cent of the 

 ship's length. This percentage was found in the investigations referred to above 

 to give about the minimum residuary resistance for the speeds attained in practice 

 for ships of this type. 



In Fig. I, Plate 96, are shown the lines of model 2,023 which were used as 

 the parent form. In Fig. 2, Plate 97, are shown the curves of sectional area for 

 the four models and the parent form. Model 2,132 was made very full at the en- 

 trance, with a fine run. Model 2,135 was made relatively very fine at the entrance 

 and full in the run. Models 2,133 ^"d 2,134 were intermediate between the two 

 extreme models. The model with the very full bow and that with the very full stern 

 were purposely made of an extreme type beyond anything that might be expected to 

 be used, in order to give a wide scope to the investigation and to insure that the lim- 

 iting condition as regards power should be obtained at either extreme. 



In the four models the middle section of the parallel middle body — that is to 

 say, the section which divided the parallel middle body into two equal portions — 

 was placed at varying distances from the forward perpendicular, amounting to 31.3, 

 38.5, 53.4, and 60.5 per cent of the length of the ship, respectively. 



"Speed and Power of Ships," by D. W. Taylor. 



