Translated articles
Analysis of the accident of the MV Nakhodka. Part 1. Estimation of wave loads*
IWAO WATANABE1 and HIDEOMI OHTSUBO2
1 Ship Dynamics Division, Ship Research Institute, Ministry of Transport,6-38-1 Shinkawa, Mitaka, Tokyo 181-0004, Japan
2University of Tokyo, Tokyo, Japan
Abstract： MV Nakhodka collapsed and broke in two on January 2, 1997 in the Sea of Japan, giving rise to a serious and disastrous oil spill on the coastline of Japan. During the inquiry into the cause of the accident, one of the main tasks of the inquiry committee was to identify the external loads which made the ship structure collapse. Among the several possible scenarios for the accident, after careful examination, the wave loads in the heavy weather at the time of the accident were taken to be the most plausible cause. The results of that research are described in two papers, and the present paper deals with the way in which wave loads on the Nakhodka at the moment of the accident were estimated. We first describe the details of the accident such as the location, the sea condition, the loading condition, and the ship's heading speed. Then the static loads resulting from the distribution of the cargo weight and the buoyancy are given to show that the static bending moment at the time of the accident caused extreme sagging. Next the wave loads in the irregular waves, calculated by the nonlinear time domain simulation program SRSLAM, are presented. It is shown that the bending moment in the waves reaches 1087 800KN*m at maximum SS 6.9, which is where the hull girder collapse took place. It was concluded
that the ship broke in two because the bending moment exceeded the hull girder strength which had been reduced due to corrosion, taking into account conclusions derived from the research dealing with the structural strength aspect. We also discuss the stochastic significance of the estimated value and nonlinear nature of the peak distribution, in addition to the effects of the ship speed and wave heading on the wave load estimation.
Key words： Nakhodka, wave load bending moment hull girder strength
Address correspondence to： I. Watanabe
Received for publication on Dec. 24, 1998; accepted on Jan. 26, 1999.
* This article is based on an article that appeared in Japanese in the Journal of the Society of Naval Architects of Japan, vol. 183 (1998).
Introduction
A Russian tanker, the Nakhodka, sank in the Sea of Japan after collapsing and splitting her hull in two in heavy weather near Oki Island on January 2, 1997. The accident caused extensive damage to the environment of the coastline along the Sea of Japan due to spilled cargo oil.
It was not Japan's responsibility to investigate the cause of the accident because it took place outside Japanese waters. It was felt necessary, however, to clarify what had happened to the ship, and what measures would be effective in stopping such an accident happening again. An inquiry committee1 was established by the Ministry of Transport immediately after the accident, in conjunction with a Russian committee, to investigate the cause of the accident and to learn what measures would be effective.1
Several possible scenarios for the accident were considered in the early stages of the inquiry. One was that a heavy wave load in heavy seas forced the ship to collapse. The others were a collision with an unidentified floating object, or an explosion of cargo oil ignited by a collision. During the course of the investigation, due consideration was given to every possibility and it was concluded that insufficient supporting evidence was found for the explosion or collision scenarios, taking into account the crew's observations and the astronomically small probability of the ship colliding with a floating object in the middle of the ocean.
After intensive examination of the shipwreck and the sea conditions, the committee reached the conclusion that the most probable scenario was that the ship collapsed because of wave loads in the heavy seas exceeding the hull girder strength. This paper describes how the committee estimated the wave loads and reached its conclusion. 2 The structural strength aspect is dealt with in the second report. 3.4
