These notices seem to be rather belated but proper steps.
5] The number of watertight bulkheads, as already explained here, was specified by Nippon Kaiji Kyokai on the basis of the extensive experience and actual records accumulated for many years by the shipbuilding industry, and the requirements of various countries around the world were found to be very similar to those of Japan. The Japanese classification society recognizes the omission of watertight bulkheads if the hull strength is deemed similar to that required by its rules, but it does not mean that the society makes precise three-dimensional hull strength calculations which may sustain such recognition.
If the total number of bulkheads is reduced, resulting in a longer hold length, a situation will emerge where, in the case of loading in alternate holds with iron ore or other cargo with large specific gravity, the maximum shearing stress generated by the longitudinal bending of the hull and the bending stress at the lower end of the side frame become remarkably great and, furthermore, the bend of the double bottom, the bending stress in the athwartships direction generated in bottom shell plating, and the shearing stress at the extremities of floor plates will increase. Not a small number of bulk carriers with five holds whose dead weight exceeds 50.000 tons as in the case of the Bolivar Maru, have experienced damage in cargo holds attributable to the extra length of such holds, and the relationship between the number of watertight bulkheads and the ship's hull strength has been in the process of theoretical investigation. The smaller the number of watertight bulkheads, the more convenient cargo handling operations, but should a vessel suffer damage in the hull all at once, there might be even cases where vessels would be able to survive, if thy were fitted with more bulkheads (since they restrict the ingress of water), it would sink because of a lack of sufficient bulkheads.
With regard to respect for human lives, there should be no difference in weight between passengers and crew members and, from this point of view, we consider that the concept of subdivision permeability should not be confined only to passenger ships engaged on international voyages but extended to cargo ships. On the other hand, in the case of oil tankers suffering damage to cargo oil tanks, as a result of collision or grounding, leading to a spill of loaded cargo oil, the resulting damage to ports and harbors may be greater in proportion to the size of the watertight compartment so affected. The number of watertight bulkheads should, therefore, be carefully determined not only from the viewpoint of convenience for cargo work but also from the aspect of damage cases.
6] The survey of ships has traditionally been conducted on the basis of specified intervals. The rate of operation of vessels has recently improved in a drastic manner, accompanying a dramatic increase in hours under way as compared with those ten years ago, which resulted in more wear and tear of structural members.
It follows that the inspection of ships conducted according to hours under way is reasonable and the introduction of more strict standards of inspection, such as the requirement of internal tank inspections as part of intermediate surveys, is one way.
