Furthermore, in the context of enhanced PSC, the Japanese proposal for mandatory entry of limits to the deterioration of plate thickness in the hull structural plating thickness measurement report of the flag country was adopted as part of the 1997 revision of the SOLAS Convention. In this connection, in recognition of the diversity of technical elements involved in the safety evaluation of structural strength reflecting deterioration in plating thick-ness and the consequent need for careful study, basic re-search is now under way in this regard.
It has been increasingly observed that prior, well-planned maintenance, rather than repair after the discovery of any defect, serves not only to ensure the safety of a ship but also to reduce the overall maintenance cost and to ex-tend its useful life. Research is also being undertaken on techniques for the evaluation of the durability of hull structure taking account of deterioration over time, which are now noted as being essential for safe and reliable ships.
3-2 Fatigue and Corrosion of Hulls
Latest sophisticated analyses have revealed that the cracks in high tensile steel-built side longitudinals of large oil tankers, which occurred in the late 1980s, were fatigue cracks due to the concentration of stresses resulting from fluctuating wave pressure. This finding has led to a structural system to ease such stress concentration, which is now used in newly built large oil tankers for enhanced safety. At the same time, while previously available data on fatigue strength were collected from uncorroded plating, basic research is now under way to determine how fatigue strength varies in a corroded environment.
It was recently pointed out that corrosion in the crude oil tanks of double-hull tankers progresses more quickly than and in different forms from those in earlier tankers. R&D efforts are being made to have an accurate grasp of the situation to elucidate the mechanism of corrosion through both laboratory and at-sea experiments and to obtain hints on corrosion-preventive measures.
3-3 Monitoring of Hull Strength
One of the available methods to support safe navigation is the monitoring of hull strength. The IMO is discussing a Hull Strength Monitoring System and a Voyage Data Recorder (VDR). The latter has found its way into Article V (Safety of Navigation) of the SOLAS Convention, and some classification societies now issue special class notations for vessels equipped with a system of this kind.
Individual devices, such as monitors, for watching cargo stowage conditions are already installed and operated aboard existing ships. Attempts are now under way to develop more sophisticated systems including one for integrated monitoring of information on wave conditions, stresses arising in structural members and other relevant factors, and a method for high-speed communication of monitored information between ship and shore.
3-4 Modernization of Ship Operation and Establishment of Management Systems
Automating and enhancing the reliability of various systems on board in pursuit of further labor saving has been a subject of study over the last few years. However, especially aboard Japanese vessels, manning with a mixed crew of Japanese officers and foreign ratings is now a usual practice on account the high cost of Japanese sea-farers and the scarcity of skilled crew members. While the crew quality is a vital factor to safe navigation, experienced seafarers are no longer readily available as they were before, resulting in an urgent call for the development of a navigation system which would allow even unskilled seafarers to operate the ship safely. Now under study is a system which, using expert systems based on the knowledge of highly skilled seafarers in combination with various individual automation systems, would let anybody operate a ship readily and safely. Major requirements for such a system include simplicity, reliability and handling ease along with the incorporation of the latest in fuzzy logic and neural network theories. Also coastwise shipping, which plays an important role in domestic transportation, shortage of labor and aging of the existing workforce are posing grave problems, and research is also being made as to how state-of-the-art technology can be applied to these coasting vessels for the modernization of their service.
It is perceived hat safe navigation requires addressing software aspects as well, and in this context the IMO in 1994 adopted the ISM Code calling for the establishment of a ship operation management system; the code be-came effective in July 1998.
Under this new operation management system for ships, the shore versus on-board duties, responsibilities, authority and mutual relationship are unequivocally defined as is the requirement to install a Safety Management System (SMS) on board for the purpose of ensuring safe navigation and environmental protection.
In order to establish a feasible SMS, the shipping and shipbuilding industries have been engaged in joint research since 1998 to find out the most appropriate operation system for ships through definition of what an easy-to-operate ship is, from both hardware and software points of view.
