HYDRODYNAMICS IN SHIP DESIGN 



Sec. 77.17 



20 



25 



45 



30 35 40 



Lenqth, ft 



The Upper Curve Represente Good Practice for Planinq Croft as of 1953. The Lower Curve Is for Hioh-Speed 

 Ploninq Hulls [ Phillips-Birt.D., "Motor Yacht and Boat Desiqn," Coles, London, 1953, p. 147] 



Fig. 77.H Relationship of Length to Beam for Planing Craft in General and High-Speed Planing 



Hulls in Particular 



Sect., 12 Jan 1955, PI. 5]. Two other chine plan- 

 forms are shown m SNAME RD sheets 116 and 

 .147. 



The shape and position of the chine line in 

 elevation (as projected on the centerplane) have 

 a certain influence upon the shape which can 

 be or is given to the transverse sections. Con- 

 versely, the shape given to the sections has a large 

 effect upon the curvature and position of the 

 chine, with respect to the at-rest waterplane. 

 Little information is available in the literature, at 

 least so far as actual or optimum characteristics 

 are concerned, relative to the height of the chine 

 above or below the designed waterline, its shape 

 and curvature, the amount of chine exposed when 

 the vessel is at rest, and so on. To correct this 

 situation in some degree the graph of Fig. 77.1 

 shows the position in profile of the chine line for 

 some representative planing craft. The chine-line 

 elevations are laid down on a constant length of 

 at-rest waterline, divided into 10 equal station 

 spaces, numbered from forward aft. The height 

 of the chine above or below the designed waterline 

 is given in per cent of the L^i, . 



The following comments are furnished con- 

 cerning the behavior of the boats represented in 

 the diagram: 



A. Luders 18-ft tender. A very satisfactory Uttle 

 craft. When planing it rides high on its extreme 

 after end, with its forefoot out of water. A cross 

 breeze acts to blow the bow off course, making it 

 necessary to meet the puffs with the helm. With 

 such a high chine forward the volume abreast it 

 is considerably reduced. Large weights must be 

 concentrated aft. This produces a planing hull 

 which rides high but it reduces the pay-load 



capacity. It is suitable principally for small boats. 



B. Huckins 33-ft pleasure criiiser. These hulls have 

 consistently run at high speeds. They have excel- 

 lent planing quaUties and are safe in heavy 

 weather. 



C. U. S. Coast Guard 40-ft utihty boat. This craft 

 has good rough-water behavior but is somewhat 

 wetter amidships than a similar boat with a round 

 bottom. 



D. Motor torpedoboat, Lwl = 66.5 ft. This craft 

 has low resistance and excellent performance in 

 smooth water but it pounds very heavily in 

 rough water. 



E. EMB Series 50 parent form. This was designed 

 many years ago and is not a particularly good 

 planing hull. It pounds in rough water. 



F. U.S.S. PT 8. A good performer in rough water 

 but has high quiet-water resistance. Undoubtedly 

 its form could be improved by better section 

 shapes. 



G. German S-boat of World War II; chine eleva- 

 tion not shown in Fig. 77.1. The V-bottom design 

 of these craft was 112 ft long on the at-rest 

 waterline and at 42 kt the T", was 3.97. The chine 

 crossed the DWL at Sta. 2.58. Its elevation at 

 the FP, Sta. 0, was +0.0375Ln.i,; at the AP, 

 Sta. 10, it was -0.017L„.i, [U. S. Naval Technical 

 Mission in Europe Rep. 338-45 of Aug 1945 

 (copy in TMB library)]. 



From the foregoing it appears that the planing 

 boats with records of good performance, especially 

 in rough water, have relatively high chines 

 forward. This of course means that the forward 

 sections can be and are made finer, mth large 

 rise-of-floor angles. Considering these factors and 



