916 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. X3.2 



TABLE X3.a — Reference Data for Standard Water 

 All data are for a water temperature of 59 deg F or 15 deg C and a latitude of 45 deg. All logarithms are to the base 

 of 10. 



Supplementing the foregoing, the head of standard salt water corresponding to a pressure intensity of 1.00 psi is 

 144/64.043 = 2.2485 ft. A head of 1.00 ft is equivalent to a pressure intensity of 64.043/144 = 0.4447 psi. 



The head of st.andard fresh water corresponding to a pressure intensity of 1.00 psi is 144/62.366 = 2.309 ft. Conversely, 

 a head of 1.00 ft is equivalent to a pressure intensity of 62.366/144 = 0.4331 psi. 



of Ships." In the meantime, ship designers re- 

 tained the round numbers of 36 and 35 previously 

 described. 



As model-basin practice became more refined 

 and as the use of Reynolds number and other 

 non-dimensional ratios increased, there arose a 

 need for accurate values of the mass density 

 p(rho) for salt water and fresh water, represented 

 by the ratio of the weight density or weight per 

 unit volume w divided by the acceleration of 

 gravity g. The round numbers for the ratios 

 64/32.17 and 62.22/32.17 were taken by many as 

 1.99 and 1.94, respectively. Others took 2.0 as a 

 round number for 1.99 and 1.0 as a round number 

 for 0.5p. The ratio of 1.99 to 1.94 is 1.026, which 

 corresponds to the sea-water specific-gravity 

 figure used in Europe for many years. 



The need for adopting a single reference tem- 

 perature for comparing the results of model tests 

 and for working up predictions of ship perform- 

 ance has led to the adoption of an international or 



ITTC standard, which is 59 deg F, 15 deg C. 

 This is a reasonable engineering average for the 

 waters of the world although somewhat low for 

 model-basin water in general. The latter averages 

 about 68 deg F, or 20 deg C. Ocean temperatures 

 range from about 86 deg F, 30 deg C, in the 

 tropics to about 28 deg F, —2.2 deg C, in the 

 polar regions. Temperatures in the open water 

 of the Great Lakes average about 47 deg F in 

 the seasons open to navigation. To permit ship 

 machinery to operate with reasonable efficiency 

 anywhere in the world a maximum injection-water 

 temperature of about 75 deg F, 24 deg C, should 

 be used. 



The standard reference temperature for water 

 is intended to be used only for analysis or com- 

 parison work. It is employed for making pre- 

 dictions only when no other temperature is 

 pertinent or is specified. If a ship is designed to 

 run primarily in the polar regions or in the tropics, 

 the values corresponding to the respective sea 



TABLE X3.b — Supplementary Data on Water 

 Characteristics of ocean water of D. W. Taylor and the U. S. Experimental Model Basin, at a temperature of 50 deg F, 

 10 deg C, as embodied in the 1910, 1933, and 1943 editions of "The Speed and Power of Ships" and other pubhcations. 



