Effect of cross water currents on a representative navigational ship in Egypt

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Ass. Lecturer, Civil Engineering Department, Faculty of Engineering, Shobra, Banha University (EGYPT) E-mails: msalama@eng.cu.edu.eg, moteleb@nwrc-eg.org, gelsaeed@feng.bu.edu.eg, mabolhars80@yahoo.com DOI: 10.7813/2075-4124.2013/5-4/A.40 ABSTRACT For studying the effect of cross water currents on navigational ships, a representative design ship was chosen based on statistical analysis of the available data for ship units along the River Nile within Egypt. In this study, a distorted scale model of 1:80 in the horizontal direction and 1:20 in the vertical direction was designed. A wooden ship, which is specified as the geometrical model of a design representative prototype ship was tested in a rectangular flume inside the north experimental hall of the Hydraulics Research Institute (HRI). The aim of this study is to develop a set of dimensionless curves, as shown in Appendix (B). The main benefit of these curves is to produce the transverse movement of the representative design ship. This movement should be utilized to check that the navigational ship doesn’t go out of its permitted maneuvering lane, according to the specifications given by (PIANC & IAPH, 1997). Hence, this result can be used to accomplish suitable designs of outfall structures, the proper design of guide pier downstream barrage components, or to verify the safe navigable path through bends. This is all to provide operational traffic safety for passing ships along the River Nile within Egypt. Key words: Safe inland navigation; cross water currents; transverse flow velocity; representative ship; ship transverse movement 1. INTRODUCTION The subjected ship area under the water surface level, which is mainly called the draught, can be considered as the most effective factor for ship stability against the transverse velocity components from any field of cross water currents. These cross currents can be encountered at river crossings, stream bends, intake and outlet structures of water plants, inlets of branched canals, and in the approach zones to navigation locks. This instability in ship navigation while passing through these previously mentioned fields is because of the generated hydrodynamic forces due to acting transverse flow velocity components. Such velocity components could affect ship navigation by complete lateral drift across its course which may reach two times the ship width and/or rotation in the vertical ship axis, (Ross, G., 1984). As a result of this shift in the ship’s course, collision hazards with other nearby passing ships may arise. For this reason the permissible cross velocity on the ship is limited to 0.3 m/s (Novak 1996; Romisch 1998; Linke & Zimmermann, 2001). Therefore, the studies in Egypt, (HRI 1997; HRI 1999; and HRI 2001), took this value as a reference without proper studies taking into consideration the River Nile’s circumstances. The present study deduced that the lateral transverse movement of the navigational unit and its rotation doesn't depend on the above mentioned value, but other different factors should be taken into consideration to ensure safety for navigational ships along the River Nile in Egypt such as: the ship’s parameters (mass, width, length, draught, and speed), the fairway’s characteristics (depth, width, and velocity), and the cross water current field conditions, such as distance to the ship, width, inclination, and magnitude. Consequently, a total of 135 experimental tests were carried out to develop a set of dimensionless curves. These curves involved representative ship parameters (width, draught and speed), fairway specifications (depth and width), and the magnitude of the transverse flow velocity component and its inclination to the flow direction. However, it was very difficult to study and simulate both the rudder angle effect and the behavior of the ship model while moving against stream. This simulation also wasn’t easy (PIANC, 1992; Anthony F. Molland, 2011) due to the following reasons: the effects of time-scale distortion due to Froude scaling between velocity and distance ratios, human judgment, and available tools and equipments through this study. Nonetheless, the negligible effect of the rudder angle will produce the maximum deviation of the ship which of course becomes its critical deviation value. This is all to produce the transverse movement of the representative ship and make sure that the navigational ship doesn’t leave its maneuvering lane.