Furthermore, the stresses at the lower ends of side frames in the middle portions of both holds were considerably great in value, raising the possibility of creating cracks if combined with poor workmanship. In such circumstances, it is presumed, the inside of ballast tanks underwent corrosion more than expected during her service for three years and three months, and stresses were concentrated in corroded and, as a result, worn parts of steel structural members of the hull; those resulted in a fracture near the No. 2 cargo hold. The state of the fracture of the hull cannot be inspected and, but such causes as the improper workmanship of the bell mouth in the No. 1 fuel oil tank and the failure of welding work, in addition to a suspicion of irregularity in the use of steel products, may, singularly or in combination, have led to the fracture. It is, hence, impossible to determine the cause of the accident in question.
The act of the Second Engineer, examinee, cannot be said to have formed a cause contributing to the occurrence of the accident in question.
We are of the opinion that we cannot determine whether the acts of the Manager Director of Ishikawajima - Harima Heavy Industllies Co, Ltd. and the Senior Managing Director of Japan Line Ltd., both disignated persons in the marine accident, contributed to the occurrence of the accident.
In relation to the occurrence of this casualty, items deemed necessary to prevent a recurrence of this type of accident are as follows:
1] When designing and constructing vessels with new structural features which are not specified in standards, highly accurate calculations should be made until after sufficient operational data on this type of ship are gained, in addition to prudent consideration given to stowage and cargo weight. In the age before the emergence of such large-sized ships as found in the present days, shearing stresses were generally small in value and, as a result, they did not seem to be considered that important. With recent large-sized vessels, the plate thickness has not grown in proportion to the size of the vessel and it is often the case that shearing stress reach an excessively large value. From now on, special attention should be paid also to the value of shearing stresses when designing a large-sized vessel.
2] External forces, particularly those exerted by waves and swells, have not been sufficiently understood in some respects and, in order to have more accurate methods to calculate hull structures, it is required to proceed with experimental and theoretical studies to examine all the aspects of the external forces caused by waves and swells through such methods as measurement in relation to actual vessels, experiments on model ships and application of structural analysis.
The casualty in question occurred in heavy weather conditions which may be encountered in the winter North Pacific Ocean every year. There are people who cite, as causes of accidents, unimaginable huge external forces exerted by waves and swells or tremendous forces other than waves and swells, or weak spots somewhere in the hull which could not be thought of from the ship's structure and size. Putting away an accident under a veil of 'immeasurability ' without much consideration may result in shouldering unnecessarily disastrous consequences of an accident on her crew members and not contributing to the clarification of the cause of this type of casualty.
