Application of Wavemaking Resistance Theory 



SHIP DESIGN AND MODEL EXPERIMENT 



Having finished the ground work in the first part, we now proceed to the 

 second part of this research project. A number of ships will be designed and 

 their models will be built and tested for resistance as well as self-propulsion. 

 In each design problem, two models will be designed and built. The first one 

 will have a simple stern profile. It will be tested for resistance only. The the- 

 oretical wavemaking resistance curve will be computed for comparison with the 

 experimental curve. The second model will be obtained from the first one by 

 modifying the afterbody for the purpose of self-propulsion tests in such a way 

 as to obtain better propulsive characteristics. However, the original afterbody 

 sectional area curve will be kept intact as much as possible. 



One ship design has been started already, and the first model is now under 

 construction. Perhaps it is worthwhile to discuss some of the thoughts incorpo- 

 rated in the design of this model. 



The design conditions are very broad. It is required to develop a fast cargo 

 ship with a displacement of 21,500 tons and a designed speed of 24 knots. A ship 

 length of 550 ft will give a V/ypL value of 0.98 and a A/(L/100)3 value of 129. If 

 normal practice is followed, a ship length of more than 550 ft would be chosen. 

 Based on the idea of reducing viscous drag, we limit the ship lei^th to 500 ft. 

 This will increase the designed speed-length ratio from 0.98 to 1.07 and the 

 displacement-length ratio from 129 to 172. 



A bulb of moderate size has been adopted for the purpose of reducing eddy- 

 ing underneath the flat bottom. This bulb is placed above the base line so that 

 the keel line is bent upward toward the bow. In doing so it is hoped that the 

 favorable flow condition on the bottom of Model 4946 will also exist on this de- 

 sign. We have thus shaped the bow first entirely from the consideration of re- 

 ducing eddying. Then the main hull is optimized in conjunction with the chosen 

 bulb such that the forebody free-surface disturbance is very small. 



To start with, only Eg shown below is used to generate the bulb. 



Eg = .01 + .05^2 ^ _08^^ (13) 



with -0.8 < ^ < . E^o has not been included here in order to avoid excessive 

 narrowing between the bulb and the main hull. 



The next item to be considered is the ^-surface. It has been found that sat- 

 isfactory results can be obtained by approximating the ^-surface waterline to 

 the sectional area curve of a Standard Series Model with about the same pris- 

 matic coefficient as the model under consideration. The width and the depth of 

 ^-surface as well as the singularity distribution placed on it determine the LB 

 and B/H ratios of the design. To start with, the width and depth of T7-surface 

 are estimated. Satisfactory solution is obtained by trial and error. 



From the eight available singularity distribution elements, we arbitrarily 

 chose Ej and E3 for the main hull. The only restraint imposed upon the opti- 

 mization is the required displacement volume. However, if the midship section 



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