Sec. 1^.1 



FIXEID-APPENDAGE DESIGN 



681 



Not More Thon 

 About 



Direction of Motion 



Fig. 73. E Boat-Tail Strut-Arm Section for High 

 Speed 



The open ditch made by the shaft may be large 

 enough so that the water clears the strut arm 

 altogether. 



It is often possible to place a fixed single-arm 

 strut abaft the propeller and to use it as the 

 forward or fixed portion of a compound rudder. 

 The forward edge of the rudder blade is close 

 behind or is mounted inside the after edge of the 

 strut arm. 



73.7 Appendages for the Arch-Stem ABC 

 Design. Sec. 67.16 describes the general con- 

 siderations governing the design of appendages at 

 the after end of the ABC ship with the arch-type 

 stern, as well as some of the details. A few addi- 

 tional notes are added here to cover certain 

 features illustrated subsequently in the following 

 drawings: 



(1) Contra-struts abaft propellers, Fig. 73. F of 

 Sec. 73.8 



(2) Short bossings for propeller shafts. Fig. 73. H 

 of Sec. 73.9 



(3) Large propeller, built up by welding, with 

 flange connections to shaft, and twin rudders 

 abaft twin skegs. Fig. 74.L of Sec. 74.15. 



The arrangement developed for the first pre- 

 liminary design and indicated schematically in 

 Figs. 73. F and 74.L embodies: 



(a) An integral forward bolting flange, propeller 

 hub, and after shaft or propeller journal of steel, 

 eliminating all taper fits, keys, threads, propeller 

 nuts, and the like 



(b) An after shaft or propeller journal which is 

 short and of large diameter, with adequate stiff- 

 ness to prevent bending and to insure reasonably 

 uniform loading of the bearing surface 



(c) Separate propeller blades, bolted to the shaft- 

 hub-journal combination with circular flanges, 

 studs, and nuts in the orthodox fashion for a 

 built-up adjustable propeller 



(d) As an alternative to (c), separate propeller 

 blades which are removable but not adjustable. 

 Eliminating the pitch-changing feature and the 

 necessity for circular blade flanges may make the 



built-up propeller more simple and sturdy, with 

 a smaller hub diameter. 



(e) As an alternative to (c) or (d), separate 

 blades of alloy or corrosion-resisting steel. These 

 may be solid or, as in an Italian proposal, may 

 be of hollow cellular construction, with welded 

 parts of steel plate [SBSR, 1 Oct 1953, p. 459]. 

 Each blade may have its own root palm or flange, 

 welded to the steel hub and to the adjacent palms, 

 or the blades may be welded to short stubs, made 

 integral with the hub, illustrated for the quad- 

 ruple-arm strut hub in Fig. 73. F. 



(f) A propeller-bearing sleeve which is mounted 

 in its housing at an angle approximating that of 

 the slope of the propeller journal when all parts 

 are in place 



(g) A propeller-bearing sleeve which is withdrawn 

 aft from its housing, to afford ample clearance for 

 the propeller journal when installing the propeller 

 assembly or removing it from the ship 



(h) A propeller journal surface of heavy chrome 

 plating with a ground finish, thus eliminating a 

 bronze sleeve which might cause corrosion of the 

 propeller journal and the hub 

 (i) A strut hub of cast steel with the usual internal 

 circumferential lands for carrying the shaft- 

 bearing sleeve. To the outside of this hub are 

 cast four short arms, curved in contra-fashion to 

 permit the inner or shaft ends of the strut arms, 

 fabricated from heavy rolled plate, to be butt- 

 welded to them. The fillets at the forward and 

 after ends of the strut-arm connections at the 

 hub are incorporated entirely in the short arms, 

 cast integral with the hub. 



(j) A readily removable exposed rotating pro- 

 peller shaft, attached by bolted flanges to the 

 flanged propeller hub at its after end and to the 

 flanged stern-tube shaft at its forward end 

 (k) A rotating shell forward of the propeller to 

 cover the bolted flange and to serve as a fairing 

 into the propeller hub 



(1) A fixed conical cap of suitable shape and pro- 

 portions abaft the propeller-bearing housing or 

 strut hub, forming the after end of the stream- 

 lined assembly comprising the rotating shell, the 

 propeller hub, the strut hub, and the tail fairing 

 (m) A suitable means of inducing adequate water 

 flow through the propeller bearing for lubrication 

 and cooling. A flared rope guard at the forward 

 end of the strut-bearing hub and a large hole in 

 the after end of the fixed fairing cap, opening into 

 what would be a separation zone or a swirl core 

 abaft the hole, should be sufficient for this purpose, 



