2.3. Ship behavior, mooring loads and tsunami situation, according to the captain׳s report
The duration of this investigation has been established as 4200 s between 14:46, when the earthquake occurred, and 15:56 when the first tsunami wave hit the VLCC, because the ship׳s captain ordered main engine actuation frequently after 15:56 and had both anchors released. Table 3 summarizes the situation regarding the ship׳s behavior, the mooring lines and the tsunami around the VLCC in a time series, which has been put together using the captain׳s report and those from the crew. From the description in Table 3, one breast line and one spring line (L19 and L20), which were comparatively short lines, were broken by the large ship motions during the earthquake, and all the stern lines were slacked. The berth master and the ship׳s captain ordered and tried to conduct emergency ship unberthing. However, they decided to remain at the berth (mooring harborage) because it was too late to do that. Thus all the mooring lines, 18 lines, were tensioned before the tsunami hit. First, the violent negative tsunami wave (wave goes out) began, and then the positive tsunami wave hit the VLCC. The VLCC moved forward with upward movement from the positive wave. The tsunami height rose until the platform of the loading arm sank. During the tsunami strike, the mooring lines were broken sequentially, from the stern lines to other lines, by the ship׳s forward movement. In addition, the ship׳s forward movement caused a big noise due to friction between the ship׳s hull and fenders. Then the captain ordered the crew to use the main engine as full astern engine to reduce the ship׳s extreme forward movement. After that, the ship stopped, and moved backward rapidly. Furthermore the captain ordered full ahead engine. Table 4 shows the situation of mooring lines breakage for each line. It is recognized that there are two types of mooring line breakage. The first type is immediate line breakage from the large ship׳s movement, and another type is line breakage after reaching the limit of the winch brake, at which point the line is pulled out of the drum.