Sec. 7'y.7 



HULL SMOOTHNESS AND FAIRING 



743 



Fig. 75. E Roughnesses and Discontinuities ox a 

 RuDDEB Horn and Ruddeb 



of appendages in general. Specific problems are 

 discussed in the sections following. 



There is no excuse, from the point of view of 

 hydrodynamics and propulsion, and little reason 

 from the structural standpoint, for fitting external 

 strut-arm pads with their bases projecting beyond 

 the fair surface of the ship. This is especially true 

 in an age which is blessed with welding and other 

 improved methods of attaching structural parts 

 to each other. At times the pads must be mounted 

 external to the shell, as on some wooden vessels. 

 The projecting edges are then reheved with a 

 large radius on the forward edge and along the 

 sides, supplemented by a long taper on the after 

 side of the pad. 



There appears to be no more excuse for leaving 

 exposed the heads and nuts of bolts connecting 

 the palms of rudder stocks and rudders, consider- 

 ing the infrequency with which they are disturbed 

 or removed. Certainly it is incongruous to smooth 

 and fair everything else in the vicinity but to 

 leave a half-dozen or dozen of these sharp- 

 cornered fastenings projecting into the flow 

 ISBSR, 27 May 1954, p. 10 of Advt]. In the same 

 fashion it is inconsistent to shape a strut or a 

 rudder section to some very special streamUned 

 form and then to plaster it with thick plates of 

 zinc which must make the water wonder what the 

 naval architect or shipbuilder expects of it. Fig. 

 75. E is a good illustration of what not to do in the 

 way of roughening the surface of a horn and a 

 rudder lying in the outflow jet of a propeller. 



75.7 Recessed Lifting and Mooring Fittings. 

 It is frequently the practice to apply a veritable 

 multitude of external padeyes, clips with lifting 

 eyes, and eyebolts to the shell plating in the run. 

 These permit the easy and quick attachment of 

 lifting devices and tackle for the handhng of 

 propeller blades, rudders, exposed shafts, and 

 other demountable underwater parts when in 

 dock. The practice is by no means limited to small 

 vessels, or to those of slow and medium speed. 

 Many, if not most of the fittings are under water 

 at the designed-load draft, particularly when the 

 stern-wave crest is taken into account. Individ- 

 ually, the pressure drag resulting from each of 

 these fittings is small, but collectively they 

 present a formidable impediment to the motion 

 of the ship. Furthermore, many of them throw 

 spray when underway. They give anything but a 

 neat, trim appearance to a run which is supposed 

 to embody everything that the naval architect 

 and the shipbuilder have learned about stream- 

 lining in the past several decades. 



The handling of aircraft on flight decks that 

 must remain smooth, and the tight fits of air- 



Floor Plate Takes 

 Lifting Load 



Alternative Recessed Liftinij Fitting 



Shell Plotinq | | 



- -J 1 I ~ 



3 '2 



Fig. 75.F Recessed Lifting Fittings 



