684 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 73.9 



(b) Simpson, G., "The Naval Constructor," New York 



and London, 4th ed., 1919, p. 59 



(c) Baker, G. S., SD, 1933, Vol. I, Fig. 7, p. 14 



(d) Hughes, G., "Model Experiments on Twin-Screw 



Propulsion, Part I", INA, 1936, pp. 145-158 and 

 Pis. XVI-XX. Four bossings with very small 

 termination angles are shown on PI. XVII. 



(e) Eggert, E. F., SNAME, 1939, Fig. 52, p. 329, shows 



the bossing sections of EMB model 3383, stern S-Sj 



(f) Van Lammeren, W. P. A., Troost, L., and Koning, 



J. G., RPSS, 1948, Fig. 54, p. 99 



(g) Baker, G. S., INA, 1952, Fig. 13, p. 109. This shows a 



bossing symmetrical about the bossing plane, with 

 a termination slope angle of 21 deg. 

 (h) De Rooij, G., "Practical Shipbuilding," 1953, Fig. 

 252b on p. 105; Fig. 561 on p. 241; Figs. 562 and 

 563 on p. 242. 



When shaping the bossing termination, the 

 propeller deserves all the edge clearance which can 

 be afforded ahead of it, consistent with proper 

 support of the propeller bearing and adequate 

 rigidity of the bossing structure. 



The actual termination, inboard of the barrel 

 portion around the propeller bearing, deserves as 

 much attention with respect to fining as the 

 termination of a shaft strut. This is much more, 

 incidentally, than has often been accorded it in 

 the past. The sections through the bossing term- 

 ination in Fig. 73. G, developed by the Newport 

 News Shipbuilding and Dry Dock Company for 

 the S. S. Talamanca and class, indicate what can 

 and should be done in this respect. They afford 

 the propeller full opportunity for doing its best 

 in the water trailing abaft the bossing. It is not 



surprising that the vessels to which these bossings 

 are fitted have given over two decades of successful 

 and satisfactory service. It is adequate proof that 

 large apertures, small slopes in the bossing flow- 

 planes, and sharp trailing edges are compatible 

 with strength, rigidity, and ease of fabrication. 



The cantilever rigidity of the heavy frame 

 carrying the propeller shaft bearing must certainly 

 be adequate. Nevertheless, some ships have 

 carried excessively blunt terminations in the 

 past which spoke only too eloquently of a struc- 

 tural design that almost crowded out the hydro- 

 dynamic design. 



The designer must decide whether the cylin- 

 drical or conical barrel which houses the shaft and 

 the propeller bearing should attach to the bossing 

 tangentially or radially. It is possible to favor 

 structural, mechanical, and other considerations 

 provided the flow over the entire bossing surface 

 is free from eddies, crossovers, and abrupt 

 changes. For example, if the plane of the bossing 

 termination is offset from the shaft axis, as in 

 Figs. 36.D and 73. G, the reentrant angle at the 

 bearing hub should be not less than 90 deg. 

 Further, the bossing surface on the "full" side 

 need not project much beyond the bearing hub. 



The design rules set down in the foregoing for 

 long, straight bossings at the stern apply also to 

 those which might be fitted for twin bow pro- 

 pellers on an icebreaker, or for bow and stern 

 propellers on a ferryboat. 



Short bossings are used primarily to fair an 



Shell PiQt 



Fig. 73, G Twjn-Sorew Bossing Tisbmination Casting fob S. S, Talaimnca and CijAss 



