PRINCIPLES OF NAVAL ENGINEERING 



WATERLINES 



\ 



V B ^-~ _. 



DIAGONALS 



B 



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Figure 2-33.— Horizontal planes and half-breadth plan. 



forward and after perpendiculars is known as 6-foot waterline, an 8-foot waterline, a 10-foot 

 the middle perpendicular. waterline, and so forth. 



An actual body plan for a YTB is shown in 

 figure 2-32. Note the projection of the diagonals 

 on this body plan. 



HALF-BREADTH PLAN 



To visualize the half-breadth plan, we must 

 imagine the ship's hull cut horizontally in 

 several places, as shown in part A of figure 

 2-33. The cuts are designated as waterlines . 

 although the ship could not possibly float at 

 many of these lines. The base plane which 

 serves as the point of origin for waterlines 

 is usually the horizontal plane that coincides 

 with the top of the flat keel. Waterlines are 

 designated according to their distance above 

 the base plane; for example, we may have a 



The waterlines are projected onto the half- 

 breadth plan, as shown in part B of figure 2-33. 

 Since the hull is symmetrical, only half of the 

 waterlines are shown in the half-breadth plan. 

 Diagonals are frequently shown on the other half 

 of the half-breadth plan. 



SHEER PLAN 



To visualize the sheer plan, we must imagine 

 the ship's hull cut vertically in several places, 

 as shown in part A of figure 2-34. The resultant 

 curves, known as buttocks or as bow and but- 

 tock lines , are projected onto the sheer plan, 

 as shown in part B of figure 2-34. The center- 

 line plane is designated as zero buttock . The 

 other buttocks are designated according to their 



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