Ships have recently been getting larger and larger in size due to the rapid development of shipbuilding technology and the increase of the quantity of cargoes transported. Because large-sized ore carrier entering the port of Pohang are getting larger, shipping companies and cargo owners ask the minimum of under-keel clearance to be permitted. At the present time the maximum size of ships entering Pohang port is the deadweight tonnage of 250,000 and will be larger more than it in the future.
Author and other pilots in the port of Pohang have experienced that when large-sized ore carriers are approaching No. 10 berth of Pohang port, they tend to turn to the left rapidly whenever the astern engine is used, the phenomenon of which is quite different from the text book of maneuvering, saying that the ship's head turns to the starboard.
In viewing this, this paper is to look into the causes of the phenomenon considering the conditions of occurrence at that time. That is, we are just trying to suggest the possible causes of rapid left-turn preceded by astern engine, based on the situation at that time. As a result the following can be concluded. The main factor is lower under-keel clearance. The left-circle discharging current caused by reverse turn of propeller does not flow under the hull bottom. Rather, it hits and is accumulated at the sea bottom. The repelling force by the accumulation of discharging current is much larger than the later force of the right-circle discharging current. The factors of increasing the repelling force are thought to be the block coefficient of ship's stern, the speed used at that time, the engine order used, and the thrust produced from the engine. And also the bank effect can be considered because of the short distance between the ship's side to the pier.
In future study the test of the water tank is needed according to the various under-keel clearances, ie. h/d.