818 



HYDRODYNAMICS IN SHIP DESIGN 



Srr. 77.26 



the designed speed, the afterbody mean chine 

 beam is 9.46 ft, slightlj^ less than Be . Strictly 

 speaking, Murray's data are not applicable to 

 the present case, because they are derived from 

 models with a constant rise-of-floor angle /3. 

 However, they are used here by taking as the 

 reference angle 13 the mean of the rise-of-floor 

 angles at the midlength section and at the 

 transom. This is 0.5 (18.25 + 3.75) or 11 deg. 



The speed coefficient, based on the mean chine 

 beam of the afterbody, is 



Cv = 



V 



= J'^'-'^''^ = 2.324 (77.vi) 

 \/32. 174(9 .46) 



The load coefficient, also based on the afterbody 

 mean chine beam, is expressed as C^ in Murray's 

 referenced paper but is represented by Cld in 

 the ATTC notation. It is 



C, 



W 

 wB^c 



19,000 



64.043(9.46)' 



= 0.3504 (77.vii) 



The dynamic-lift coefficient, assuming a con- 

 stant rise-of-floor angle of /3, is 



{Cdl)» — 



O.opV'B' 



2Cl 

 Cl 



This is on the basis that the entire weight W of 

 the boat is supported by dynamic lift. Data so 

 derived are certainly on the conservative side. 



The dynamic-lift- coefficient {Cdljo for a ri.se- 

 of-floor angle of /3 = is required for the resistance 

 calculations. To determine it, enter the lower part 

 of Fig. 53. B in Sec. 53.4 with the average rise-of- 

 floor angle /3 of 11 deg and the value {Cdl)^ of 

 0.1298. The derived value of {Col) a = 0.155. 



The sum of the friction resistance Rp and the 

 residuary resistance Rr is, the total drag force 

 opposing motion, represented as the sum of the 

 forces 7 and J in Fig. 13. C. However, as it is 

 not always practicable or possible to determine 



TABLE 77.g — Resistance Calculation for Full-Planing Tender Hull of Fig. 77.K bt Murray's Planing-Surface Data 

 The data referenced in the heading of this table are found in Fig. 53.B, Sec. 53.4. 



Col. B — From small table, Fig. 53. B of Sec. 53.4, top part 



Col. C— (Cic)o from lower part of Fig. 53.B. Enter with /3 = 11°, {Cld)h = 0.1298 



Col. D— X, ratio of wetted length L^s to beam /?c ; X = Lws /Be ■ From curves of Fig. 53. B, top part 



Col. E— [(Col. P)(Bc)]; Lws = XBc 



Col. F— [(Col. E)(Bc)] 



Col. G—S = (Lws)Bc/cos p 



Col. H-i2„ = VLws/" = '•i'287('t'^r = 3.1630(10s)L„. 



Col. I— From tables, SNAME Tech. and Res. Bull. 1-2 



Col. L— [(Col. G) (Col. J)] 



Col. U—Rp = Q.5pVS[WCf + 10'(AC;,)1 = 0.5(1.9905)[1.6889(24)12S[103Cf. + lO^ACf)] 



= 1635.7 (Col. L) 

 Col. N — From standard tables 

 Col. 0—Rr = L tan 9 = a tan e 

 Col. V—Rt = Rr + Rf = Col. M + Col. O. 



