172 VARIATIONS OF SHAFT HORSE-POWER, ETC., 



D = Diameter of propeller in feet. 



P = Pitch of propeller in feet. 



T. S. = Basic tip speed (3 blades) in feet, of propeller. 



V = Actual speed of vessel. 



e. h. p. = Effective (tow-rope) horse-power for v. 



The power required to deliver e. h. p. where no cavitation exists is expressed by — 



I.H.P.rf = I.H.P. X K-^ lo'- 



where Z depends for its value upon the value ^ h p ' ^^^*^ ^ ^^ ^^^ thrust deduction factor. 



The revolutions corresponding to the actual conditions of resistance are found by the fol- 

 lowing equations: — 



. = Apparent shp= 5 ^ ^ p ^^^ 



where S is the basic apparent slip and A^. and A^ are factors depending upon the values 

 of V and v. 



It should be borne in mind that slight variations in the form of blade have only slight 

 effect upon the efficiency so long as the same projected area is retained, but do have a consid- 

 erable effect upon revolutions ; therefore we should be prepared to find but small differences 

 between the estimated and tank powers if both methods are correct, but considerable varia- 

 tion in the revolutions as the propeller used by Commander McEntee had blades of the 

 Taylor form, while the standard blade form used by me, as already pointed out, is an oval. 



In determining the block coefficient to use for basic apparent slip, the open water (where 

 the propeller is not covered by the limits of the load water plane of the ship) correction is 

 applied for Hulls 2132, 2133 and 2134, directly to the standard block as ordinarily obtained 

 for hulls of the given length, beam and displacement; while for Hull 2135, which had ab- 

 normally full after body lines, this same correction has been applied to an increased stand- 

 ard block, this block being 0.80 in the first three cases and 0.85 in the latter, the correspond- 

 ing open water blocks being 0.532 and 0.61. 



The work of analysis and estimate follows, the estimated and tank powers and the esti- 

 mated and tank revolutions being placed in parallel columns. 



Hull Characteristics. 



L.B.P. = 400' Nom. B.C. =0.7716 D <C 0.7 H. ;. 



B = 57.3' B -^ L.B.P. = 0.1433 Stand S.B.C. for V = 0.532 



H = 26' Stand. B.C. for K = 0.80 Stand S.B.C. for V 



Displ. = 13137 Est. Stand. B.C. for (Hull 2135) =0.61 



i^ (Hull 2135) =0.85 i? = 1.27; for 2135 = 1.41 



Basic Condition of Propeller. 



P.A. ^ D.A. (3 blades) 0.266 



D 16.583' 



p 14.75' 



T.S 5,900 



PXR ..- ■•■■■ 1.671 



