Sec. X3.2 MECHANICAL PROPERTIES OF AIR AND WATER 917 



TABLE X3.C — Standard Characteristics op the Water Used in Several Model Basins in North America 

 The basin water is assumed to be at an average temperature of 68 deg F, 20 dcg C. 



♦Taken from TMB Hydromechanics Work Instruction 20-25 of 3 Apr 1950. 



temperatures expected in service are used. If, 

 however, these service temperatures are not 

 known or are not specified in advance, all ship 

 powers derived from model tests are worked up 

 for "standard" salt water or fresh lake and river 

 water at 59 deg F. 



The adoption of this standard temperature 

 made it possible to prepare standard reference 

 data for water, to be employed in all model-basin 

 and ship-design work. For establishing these data, 

 the following general principles were laid down: 



(a) The ratios between the several sets of values 

 should be consistent 



(b) The "standard" values should be as close as 

 practicable to the actual average physical values 



(c) Round numbers would not be necessary, with 

 modern desk-type calculating machines available 

 everywhere 



(d) New "standard" values should be extended 

 to five (5) significant figures, to achieve con- 

 sistency, not only for sea level but for all other 

 levels 



(e) The data would cover most of the model and 

 ship activities in America if calculated for 

 sea level and for Great Lakes level. Similar calcu- 

 lations for other lake levels could be made as 

 desired. 



Table X3.a lists the reference data described 

 in the preceding paragraphs. For reference pur- 

 poses there are given in Table X3.b the corre- 



TABLE X3.d— Mass Density op FRESH WATER, Embodying Variation With Temperature 

 The values are in English engineering units of slugs per ft^ They correspond to those adopted by the American Towing 

 Tank Conference in 1939 and published in SNAME, 1939, p. 416. To convert them to pounds weight, multiply by the 

 local acceleration of gravity g. 



There are given hereunder the gravity constants, or values of the acceleration of gravity g, in ft per sec-, for sea level 

 at si.\ values of latitude. These data apply also to Table X3.e. 



15 deg 

 32.101 



25 deg 

 32.120 



35 deg 

 32.145 



45 deg 



32.174 



55 deg 

 32.203 



65 deg 

 32.229 



