Sec. 45.20 



FRICTION-RESISTANCE CALCULATIONS 



123 



The daily increments, when taken from the 

 proper "box" of Table 45.g, have to be multiplied 

 by the number of days in each operational con- 

 dition and then added to give the ApCp for the 

 effects of items (1) and (2) in the summary. The 

 locality fouling factor is then applied to this sum 

 (by multiplication) to cover the effect of item (3) . 

 The upper row of boxes in Table 45. h is left open 

 until such time as data are available to determine 

 values of the locality factor which are reasonably 

 correct, and until such time as additional ports 

 in the Western Hemisphere can be listed. 



As for item (4) of the summary, it is perhaps 

 not wise to introduce a set of ship-size and ship- 

 speed parameters into the fouling roughness pre- 

 diction procedure until the effect of these param- 

 eters is fully proved for roughnesses in general. 

 If and when so proved, the variation in A^Cf 

 with Reynolds number R„ will probably resemble 

 the variations in ACp shown by the lines C-C 

 and D-D of Fig. 45.E. 



Judging from the work done recently on this 

 project, it appears hopeless to expect that a single 

 rule, table, graph, or reference, and certainly not 

 a rule of thumb, will furnish adequate prediction 

 data for fouling on ships of all sizes and types. 



operating in all seasons and in all waters of the 

 Avorld. Nevertheless, there is a definite demand 

 for a simple guide which will give the answer 

 in one operation, as it were. 



As an interim measure a set of graphs prepared 

 and published by E. V. Lewis [The Log, May 

 1948, pp. 50-52] serves as a means of determining 

 by inspection a suitable value of AfCf{10^) for 

 any one of three given operating conditions. 

 Lewis' data are reproduced in Fig. 45.K, supple- 

 mented by data derived from the trials of three 

 ships, the U. S. destroyer Putnam (DD 287), the 

 U. S. battleship Tennessee (BB 43), and the 

 Japanese destroyer Yudachi. The two former sets 

 of data were used by Lewis; the latter data were 

 not. According to information received subsequent 

 to the date of the reference [unpubl. Itr. of 15 

 Aug 1955], curve B was actually based on the 

 British Admiralty peace-time standard for ships 

 operating in tropical waters, involving a 0.5 per 

 cent per day increase in friction resistance [INA, 

 1943, Vol. 85, p. 2]. Curve A was based on the 

 British Admiralty standard for temperate waters, 

 with a rate of 0.25 per cent per day increase in 

 Rp , raised somewhat and given some upward 

 curvature because of the shape of the curve for 



Line B is for ships 



which enter a numbei 



of ports where severe 



foulincj 



encountered 



2J 



Line A is for ships 



on overoqe vo^aqes - n 



between tcmperote 



ports with Qveraqe 



rotes of fouling . g 



Line C is for ships having 

 unusuall'y short stoys in port 

 or trodino reoulorlij between ^— 

 ports free from foulino or ports 

 havinq a scourinq action 

 I I \ L_l I L 



6 7 8 9 



Months Out of Dr\jdock 



Fig. 45.K Graphs op E. V. Lewis fob Specific Fouling Resistance Allowances, with Curves fob Thbee 



Ships 



