Sec. XI. 6 



SYMBOLS AND THEIR TITLES 



913 



Pressure 



lb in^, psi, psig — pounds per square inch; above 



atmospheric or gage pressure, unless otherwise 



specified 

 lb ft^, psf — pounds per square foot 

 psia — pounds per square inch, absolute 

 atm — atmospheres of pressure, in units of roughly 



14.7 lb in' 

 kg cm" — kilograms per sq cm, in units of roughly 



14.2 lb in' 



Moment or Torque 

 in-lb — inch-pound 

 ft-lb — foot-pound 

 kg-m — kilogram-meter 



Angles and Arcs 

 deg — degrees of arc 

 rad — radians, 360/ (2 tt) 



Power 



h — horse, a unit of power, in English units unless 



otherwise specified 

 hp — horsepower 



bhp — brake power, in English horses 

 ehp — effective power, in English horses 

 ihp — indicated power, in English horses 

 php — propeller power, in English horses 

 shp — shaft power, in English horses 



Time and Rate 



us — micro second, one millionth of a second 



ms — millisecond 



sec — second 



min — minute 



hr — -hour 



fps or ft per sec — foot (feet) per second 



fpm or ft per min — foot (feet) per minute 



cfs — cubic foot per second 



cfm — cubic foot per minute 



cms — cubic meter per second 



ops — cycles per second 



gpm — gallon per minute 



hz — hertz, frequency of 1 cj^cle per second 



rps — revolutions per second 



rpm — revolutions per minute 



mph — miles (generally geographical) per hour 



mps — meters per second 



kt — knot, one nautical mile per hour 



Temperature 



deg — degree 



deg C — degree Centigrade 



deg F — degree Fahrenheit. 



X L6 Circular Constant Notation. The several 

 symbols of the circular constant notation of 

 R. E. Froude and G. S. Baker are listed here, 



with the non-dimensional formulas which express 

 their values as multipliers of well-known 0-diml 

 numbers. Following these are the dimensional 

 forms, as applied to English units of measurement. 

 It is important that consistent units be em- 

 ployed in the formulas listed hereunder, as well 

 as in all other pure formulas, containing physical 

 concepts only. For example, in the English 

 system of measurement, units should be lb, ft, 

 and sec. The same value of g should be used for 

 all the expressions. 



@ Length-Displacement Constant. The ratio 

 of the length L of the ship to the length of the 

 side of a cube having the same volume of dis- 

 placement F or V as the ship. 



® Speed-Displacement Constant. The ratio of 

 the speed V of the ship to the speed of a wave with 

 a length equal to half the length of the side of a 

 cube having the same volume of displacement V 

 or V as the ship. 



V 



2ir2 



= V4ir 



VgV 



= 3.545F, 



© Resistance Constant. One thousand times 

 the ratio of the resistance R to the displacement 

 weight W, divided by the square of the speed- 

 displacement constant ®. Here W = wV. 



lOOOfi ¥'^ 



w v 



_9_ 

 At 



lOOOff V 



wV V' At 



= 39.79Cj 



where Ct is the total specific resistance coefficient 

 based on ¥^^^ as the reference dimension. 



(L) Speed-Length Constant. The ratio of the 

 speed V of the ship to the speed of a gravity wave 

 of length equal to half the length L of the ship. 



© 



3.545F„ 



(p) Speed-Prismatic-Length Constant. The ratio 

 of the speed V of the ship to the speed of a wave 



