Sec. 72.10 



DESIGN FOR CONFINED WATERS 



667 



Station 20 at Extreme After End of 



Station at Forward End of Hul 



-^ Ratio = 0.0432 



Rise of Floor ^ 

 about .J-S deq 



Fig. 72. E Body Plan of Hillman Pushboat with Sthaight-Element Frame Sections 



for any other type of shallow-water vessel running 

 at moderate speed. 



The reentrant angles in the forebody sections 

 forward of Sta. 2.5 prevent the flare from becom- 

 ing excessive in way of the bow wave. At the 

 same time they provide support for a wide deck 

 with its pushing pads (or for passenger accommo- 

 dations or cargo). Forward of and abaft Sta. 2.5 

 the section lines lie approximately normal to 

 the lines of flow as the water from ahead passes 

 under the vessel. In the afterbody, the extension 

 of the nearly vertical side down to a long hori- 

 zontal knuckle, lying at an appreciable distance 

 below the DWL, prevents leakage of air to the 

 propeller region, well inboard from the side. The 

 craft depicted in Figs. 72. E and 72. F was in 

 addition fitted with two Kort nozzles, shown in 

 outline only in the latter figure, which served as 

 additional shields against air leakage. Although it 

 was not possible to arrange for a flow test of a 

 model of this vessel in the TMB circulating-water 

 channel, it appears that the water flow along the 

 afterbody would likewise move easily under the 

 section lines shown. 



72.10 Bow Shaping. Shaping the bow and 

 the entrance is a much more difficult operation on 

 a shallow-water craft with a B/H ratio of from 

 4 or 5 to 10 than on a deep-water vessel, with a 

 ratio of 2.5 to 3.5. The large beam-draft ratio, 

 coupled with the usual requirements for wide 



decks in a vessel which must carry most of its 

 useful load above the main hull, produces the 

 large flares in the entrance shown on the body 

 plans of Figs. 72.A through 72.E. 



If the length is not restricted, the designed 

 waterline slopes in the entrance and run can be 

 made acceptably small, despite a large maximum 

 beam. This helps greatly to counteract the effect 

 of heavy flare in the entrance sections. The 

 entrance slope of the DWL for the Mary Powell 

 was only about 6.5 deg; that of the New York 

 about 5 deg. The maximum run slopes were 

 13.8 deg and 15.5 deg, respectively. 



A scow, sled, or spoon bow lets most of the 

 water flow easily under the bottom but when 

 the bed clearance is reduced nearly to nothing, 

 the bow must also let it flow easily around the 

 sides. Further, something approaching the shape 

 of a vertical skeg is required forward on a vessel 

 with this type of entrance to provide a stabilizing 

 or fulcrum effect for assistance in steering and 

 turning. This is the reason for the V-shaped fore- 

 foot of the Hillman design of Fig. 72.E. A. R. 

 Mitchell recommends that on full-bodied ci'aft 

 of this type the slope of the DWL forward be not 

 less than 28 deg, because at a lesser angle more 

 of the water flows around the sides and not under 

 the bottom [INA, Jul 1952, p. 148]. 



He further recommends that to facilitate this 

 under- the-bottom flow "... stem in profile should 



Fig. 72. F Outboard Profile of Hillman Pushboat 



Both Figs. 72.E and 72.F are adapted from drawings kindly furnished by the Hillman Barge and Construction Company 

 of Pittsburgh 



