782 



HYDRODYNAMICS IN SHIP DESIGN 



Sec. 76.18 



ously heavy load can be built up on the immersed 

 area of such a bulkhead by dynamic action of the 

 water, even at low speeds. Indeed, a vessel with 

 only a portion of its bow caved in, but with a 

 hole by which the dynamic pressure at that point 

 is transmitted to the boundaries of the flooded 

 portion, can develop high dynamic loads on those 

 boundaries, indicated by diagram 1 of Fig. 76. K. 



A vessel damaged in this manner can and should 

 be towed with the undamaged end foremost, 

 even to the extent of towing stern first, without 

 benefit of the steering effect of a rudder at the 

 trailing end. A photograph of a large tanker 

 without a bow, being towed in this manner, is 

 reproduced in Shipbuilding and Shipping Record 

 [5 Jun 1947, p. 559]. Under these conditions the 

 propeller is permitted to free-wheel, if practicable. 

 A combination of square leading and trailing 

 ends, such as might be encountered on a transom- 

 stern destroyer with its bow broken off, may 

 result in some yawing or weaving during a towing 

 operation. However, if the damaged vessel is 

 towed with its good end foremost, the holding 

 bulkhead should remain intact and the ship 

 should stay afloat. 



If the bow is damaged or missing, and it is 

 desired to bring the vessel home under its own 

 power, a rather blunt false bow is found adequate. 

 Straight sides and an entrance slope of 45 deg. 



sketched at 4 in Fig. 76. K, should suffice for 

 reasonably rapid travel. If head seas are likely 

 to be encountered, a rake to the false bow sides — 

 any amount that is found practicable up to 15 

 deg or so — pays for itself in easing the impact 

 loads on the flat surfaces. Because of the flat 

 sides on the temporary bow, it can be expected 

 that the wavegoing loads on the hull, at reduced 

 speed, will be at least as large as on the undamaged 

 vessel at normal speed. 



With a well-constructed false bow of the type 

 illustrated in diagrams 3 and 4 of Fig. 76. K and 

 in reasonably smooth water, it should be possible 

 to make at least one-third the speed to be expected 

 with the undamaged vessel. In fact, vessels have 

 made ocean crossings under their own power 

 with false bows very much blunter than the one 

 depicted in diagrams 3 and 4 of the figure. 

 One such ship was the U.S.S. Selfridge (DD 357), 

 which had its bow blown off in the South Pacific 

 during World War II. Fig. 76. L shows the vessel 

 in a floating dry dock with the false bow com- 

 pleted. A photograph of the vessel under way in 

 this condition is reproduced in the Bureau of 

 Ships (U. S. Navy Department) Journal for 

 May 1953, page 12. 



76.18 Floats for Pontoon Bridges. A varia- 

 tion of the box-shaped, load-carrjdng barge or 

 fighter is the moored float intended to support 



Hydrostatic Pressure 

 on IrrtQct Bulkhead is 

 Auqmented b-; B'ynomic Pressure 

 +Ap Developed at Blunt Bow 



Biacjrame 1,2, and 4 Represent Plan Views 

 at About the Surfoce Waterline 



Any Rake up to 

 15 deo IS Probably 

 of Benefit in 

 RouQh Woter 



Fig. 76. K Schematic Design for Tempor-vry Bows of Damaged Vessels 



