Lang 



The primary objective of this paper is to describe the basic 

 characteristics of an S 3 so that it can be compared with other types 

 of ships for various types of applications. To do this, the drag and 

 power, stability, motion in waves, and automatic control characteris- 

 tics will be discussed. 



DRAG AND POWER 



In calm water, ship speed is a function of drag, and is there- 

 fore limited by the installed power. The maximum speed may be less 

 in the higher sea states, since speed may be limited either by ship 

 motion or by increased drag due to waves. In the case of monohulls, 

 speed limitations in the higher sea states can be severe. 



In order to compare the drag and power of a wide variety of 

 ship forms, sizes, and speeds, the following equations are used : 



D 



drag coefficient = 



power = 



displacement Froude number = F^ = 



Vgv/3 g^/e 



A. V A 



hull efficiency = E = — — — = -=- . y 



A f A 1 _Af ' 1 



range = R = g- . q . ^r^ «— . E . 



SFC 



where D = drag, V = displaced volume, p = mass den- 

 sity of water, V = speed, 77 = propulsive efficiency, g = accele- 

 ration of gravity, A = V p g = displaced weight, A f = weight of 

 fuel, and SFC = specific fuel consumption = weight of fuel consum- 

 ed per unit power per unit time. The units used may be any consis- 

 tent set. The term Cp is the frictional drag coefficient, and is 

 assumed to be purely a f function of Reynolds number ; the term D f 

 reduces as the size or speed increases. The term C D is the 



residual drag coefficient ; it includes the wave drag and all other 

 sources of drag except frictional drag, and is assumed to be purely 



552 



