harbors and to remote islands, are also steadily increasing in speed. New types of high-speed vessels developed by various shipbuilders, including fine hull-form catamarans and craft supported on fully submerged hydrofoils, are entering service on many of these routes.
2-3 Infrastructure
A plan to build up a system for high-speed physical distribution by sea is under study, in which the newly developed TSL would play a central role. The technical challenges involved include the realization of faster and more efficient cargo handling to match the speed of marine transport. When the TSL was put through cargo carrying tests in fiscal 1995, cargo handling experiments with test machines were carried out.
In order to realize a high-speed transportation system, it is not sufficient to improve the efficiency of cargo handling alone. Rather, an efficient link should be realistically established between marine and overland modes as part of a broader system, and in this connection research is being made on the possibility of relevant institutional reform as well.
3. Safety and reliability of ships
As marine disasters involving old large bulk carriers have occurred over the years, taking heavy tolls in human lives and valuable resources, the IMO and the IACS among others are discussing the safety of old vessels and ways to address this issue. Recent social developments in general are also contributing to the attaching of increasing importance to the safety and reliability of ships.
3-1 Tightened hull inspection and maintenance
To ensure safe navigation, regular surveys and hull inspections of bulk carriers and tankers have been tightened in terms of both scope and method. For bulk carriers, for example, the IACS in 1994 set forth specific guidelines regarding inspection, evaluation and repair. For tankers, classification societies have incorporated measures for enhanced inspection into their rules. It has been made mandatory for ballast tanks which will be heavily corroded or worn to be wholly painted, and increased consideration is given to the means of access for surveyors and inspectors, at building stage.
It has become well recognized that planned preventive maintenance of vessels, rather than repairing them after any defect is found, ensures their safety and eventually helps to reduce their maintenance cost and extend their useful lives. Attention is also focusing and studies are being made on the importance of other opportunities to enhance the safety and reliability of vessels, such as the feedback of repair experience at shipyards to the planning of inspections with priority on more vital aspects, and to the designing of new vessels and, concurrently, techniques for the assesment of ships' remaining life expectancies, taking account of their deterioration over time.
3-2 Corrosion fatigue of hulls
The cause of the cracks which occurred a few years ago in high tensile steel longitudinals on side shell of large tankers has been identified by sophisticated analytical techniques as resulting from fatigue transmitted from stress-concentrating areas, which in turn is attributable to the dynamic wave pressure. This finding is reflected in the structural designs of newly built tankers which feature deconcentration of such stresses with a view to greater safety. While previously available data on fatigue strength referred only to the fatigue of uncorroded steel, basic research is now under way on the variations of fatigue strength in a corrosive environment.
3-3 Monitoring of hull strength
One of the ways now attracting attention to support the safety of vessels in service is the monitoring of hull strength. The IMO is discussing a hull strength monitoring system for bulk carriers, and some classification societies give specific class notations to vessels equipped with hull strength monitoring system. One of the experimental TSL vessels (type A) is equipped with a monitoring system which monitors the acceleration of hull motion and stresses on main structural positions, and further, statistically
