Developments in Theory of Bulbous Ships 



A circular streamlined body of L/D = 4 has been used as a basic model 

 which has later been utilized for different purposes as: the submerged body of 

 a hydrofoil supported catamaran ship, as the ballast keel of sailboat tests and 

 later as a bulb for Turkish fishing boat model tests. 



Bulbs as large as one third the length of the model were tried and interest- 

 ing results were obtained, which however not published has served to inspire 

 the visitors to Turkish Tank, to promote new strides in chapters of wave re- 

 sistance of ships with bulbs. 



The action of the bulb as to its characteristic of producing suction can be 

 visualized by the head-on trim it causes on the surface ship. This suction be- 

 comes highly distinctive when it is towed under a flat bottomed pontoon, or near 

 the water surface. 



The pictures of a fish form circular body of L/D = 3 taken at different 

 speeds are shown in Fig. 1. 



Fig. 1 - Fish form circular body- 



It is noted that, at speeds lower than (the critical Froude number for depth), 

 a wave trough is produced immediately after the bow wave of the fish, which 

 moves aft as the speed is increased. This trough, the focal point of suction 

 when coincides with the bov/ wave of the ship is swallowed in it. The effect be- 

 comes more pronounced as the bulge nears the surface. At greater speeds a 

 sheet of water covers the top and the centre of the suction moves further aft 

 over the tail. 



The ships which are sensible to trim, when fitted with bulbs, have some- 

 times indicated increased resistances, at certain speeds, due to dive in of their 

 bow, resulting from the suction produced by their bulbs, consequently increased 

 bow waves, instead of reduced ones. This will mean a wrong shape, size and 

 position of the bulb. This complex interaction of bulb and ship necessitated 



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