Sec. 74.7 



MOVABLE-APPENDAGE DESIGN 



715 



on "Steam Tug Design" [London, Jul 1946]. It is 

 still used by aeronautical engineers in propor- 

 tioning the rudders of dirigibles. 



Based upon the data in the references listed 

 earlier in this section and upon the ratios given 

 in Tables 74. a and 74. b, a few general rules are 

 formulated for use in the preliminary design 

 stage of a ship: 



of the turn are somewhat shielded from cross 

 flow by the ship ahead of them, those on the 

 outside of the turn are exposed to a greater degree 

 of cross flow. One may say that, for a first approxi- 

 mation, an average of these effects forms a good 

 estimate. 



The total absence of diagrams showing the 

 rudder profiles, the ship or large-appendage pro- 

 files, and the relative positions of the movable , , . , , , r ^, r^ ■ ,• • 



, , , , 1 , ,, ,. J. u- J 11 w A rudder, to be fully effective, must lie m a 



rudder blades and the adjacent ship render all . ^ r, i ■ > ■ n ,. 



irujjj. fiuiju -iu f region of flow which is tree of greatly reduced 

 published data of the kind shown m the references , . , ,. , , n 



., , ■ 1 • xu- i- ii-- 1 velocity, eddies, and reversed flow 



cited previously in this section as something less ,, s t,t , • ,, „ , , „ 



,, f 1 T f J. -J. j-u J. 1 1 i 1 • (b) JNo mechanically propelled vessel, regardless 



than useml. In tact, it appears that only by taking /, , ,,, ,. . ,, ' ^ , 



, P , , n , , . , .1 01 type, should have a ratio ot rudder area Ar to 



account ot these features, which govern the , , , , ^.^rs „ V 



,. c fi\ J.U J. r ii, rectangular underwater area L(H) smaller than 



proportion ot (1) the transverse force on the ,^ ,».. ,.,„ -, 



jj i ^o\ xu i i. 1 X r xi_ J l.D per cent. A minimum of 1.7 per cent might 



rudder to (2) the total transverse torce on the end , , , , ,, ,„^„ , ,, ^ -r. ,; , , , 



J. ,, , . ,, . . • , ■ r X, be better; the 1953 table of r. Mandel shows a 



ot the ship, can the major inconsistencies of the . . ,. , „ 



t-T 1, J X ui u 1 J minimum ot 1.9 per cent, 



published tables be cleared up. / s rr,, ,. i , , , , 



Tx ■ Ml XI, X r xv, 1 X- X 1 1 11 (c) I he percentage ot rudder-blade area over- 

 It is possible that further analytic study should , . f ,, ,„ ■ , , ,, ■, 

 , . , ,, J ,.,,, J • 1 1 lapping the propeller outflow let at the ruader 

 be given to a method, little-used m modern naval ., • , ; , , , ,- ,, rr^, • . 



,.,, J. ... ,, .1111 position should be as large as practicable. I his is 



architecture, ot proportionmg the movable-blade •„, ,■ , ,• ,^ 



r XI- jj X xi. -J X- f xi especially true tor vessels operating at a i „ value 



area ot the rudder to the midsection area of the ,,, ,„ , ,. „ ,,. ii,-, 



,. ■-^ X- r -vTr T HT Ti 1 • ■ -innr^ less than 1.0 and lor flows past the rudder which 

 ship. Quotmg from W. J. M. Rankine m 1866 , , r, • ,i , „ ■,, ^ 



ran^Tii itrru x • x u- u -u xi_ i x A,r are suspectcd ot being Weak, With large positive 

 [SIP: That eminent shipbuilder, the late Mr. , , .,. , „ ^ ^ ,i 



T u ITT J J XT- u jxi. J? xi 11 wake velocities and small speeds ot rudder ad- 



John Wood, made the breadth of the rudder ,, . ., , , , ■, ... 



, /oxu r xi- X r XI. I.- ji mi.- X xi J -ii vance. It is possible, as stated previously in 



l/8th ot that ot the ship. 1 his meant that, with „ „.„,,, ,, „ n -,. 



J xi. r J J I. X 1 X XI ^ i-j J^ Sec. 74.3, that a strong flow, with a large 



a depth ot rudder about equal to the draft, the i ,. , , , , „ , , 



,1 , ,, u X r. inr X- xi_ -i spced ot ruddcr advancB aud a Small overlap, has 



rudder length was about 0.125 times the mid- , ^ . . r^ . ,■, , , r , 



,- , m, . xu J f 1 X- xi more benencial effect than large overlap of the 



section beam, i lus method of selecting the proper ,, . « , ,, n 



J, .. iA/~.iJii-i-ii same rudder m a weak flow, 



rudder area is given by A. Caldwell m his book . ,s rr^, , ,. , , ,, 



(d) ihe percentage ot cutaway area and the 



TABLE 74.b-RATios of Rudder-Blade Area Aj, to ^^^^^ ^f cutaway length to ship length he within 

 Length-Draft Product (LH) for Merchant-Type rather narrow limits for the average vessel. If 

 Vessels the cutaways are adequate, the exact ratios 

 The rudder area is considered to be that of the movable appear not to be major factors in its maneuver- 

 blade only. The proportions given are for ships with single ability. 



rudders. ^^-j fp^jj-^ rudfjgj-g fgr large ships may have a 



~ combined blade area as great as 0.03L{H). A 



baseplane clearance of 0.5 ft appears to be ade- 



Liners, large, fast and high-speed 1.6-1.8 quate for any deep-water vessel, regardless of size. 



Passenger and cargo ships, large, medium-speed 1.6-2.0 (f ) When adequate draft is available and multiple 



Tankers, large, fast and medium-speed ... 1.7-2.1 rudders are used, the aspect ratio is made rather 



Passenger and cargo ships, small, slow-speed . 1.7-2.3 jarge, to give the greatest coverage across an 



a g s ps, as / " ■ outflow jet or the maximum pressure abaft a skeg. 



River steamers, fast 1 . 7-2 .0 



Cargo ships, normal, medium-speed 1.7-2.5 74.7 Determining the Proper Areas of Various 



Auxiliary vessels for national defense 1.9-2.4 /^ x i o _i; t^u • xi- j • xu- 



^ /. „ ^ „ „ „ o Control Surfaces. There is outhned m this 



Cargo ships, small; coasters 2.0-2.3 . ..... 



Cross-channel ships, required to maneuver in section a new procedure for determimng, as a 



harbors 2.0-2.2 second or third approximation, the required area 



Sailing ships, large 2.0-2.5 of the movable blade of a control surface. The 



Ferryboats for harbors, fishing vessels .... 2.5-4.0 method as described here apphes to a steermg 



w'^kh°^t''^^ 11 4. r\\ n rudder in a vertical plane but it is essentially the 



Inland waterways craft, for confined waters '. '. 4^0-8.0 ^^me for a control surface mounted on a surface 

 — ship or submarine in any other plane. 



