Conclusions and further work
Accident statistics show that collision and grounding events are some of the most frequent causes of serious accidents at sea and therefore also the most important elements in any risk summation procedure for ships.
Collision and grounding safety is at present implemented in the maritime industry by compliance with prescriptive, history-driven rules and regulations used by designers and operators and verified by classification societies and Port State Control. Thus, the development of these rules is motivated by accidents and implemented to satisfy societal concerns following the event of past accidents.
However, rational risk based analysis procedures have been used with success in connection with design and approval of offshore structures and large bridges crossing international waterways. Therefore, it seems appropriate that the international shipping community should also standardise decisions concerning elements in risk acceptance criteria. That is, establish agreement on a general form of risk criteria such as Eq. (1) and then establish a suite of connected rational tools for
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Estimation of the grounding and collision probability
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Models for calculation of the resulting grounding and collision damage
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Analysis of the conditions of the damaged vessels
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Estimation of costs associated with the accidents
With such tools it is possible to facilitate increased collision and grounding safety through rational selection and development of different risk control options.
It has been the purpose of the present paper to demonstrate that the research community has developed much of the needed basic research work. What is still needed is a concerted effort to identify gaps in our knowledge and then to integrate this knowledge into risk based procedures for ship operation and ship design. The goal should be development of new rules based on international formal safety assessment analysis (FSA). A number of FSA analyses following the procedure described in Fig. 2 have been presented to IMO in recent years, see for instance Ref. [6]. Thus, the framework for collision and grounding risk evaluation exists. At present, it is the absence of agreed on, consistent, mathematically based analysis tools which makes the current risk analyses based on expert judgments and historically based comparisons somewhat subjective and often gives rise to discussions.
A framework for introduction of such rational procedures for grounding and collision safety exists within IMO and the classification societies.
The International Maritime Organization (IMO) is developing “Goal Based Standards” (GBS) for new ship constructions. By the concept of Goal Based Standards, IMO attempts to define certain “high level” goals that must be met. Since this effort is still at an early stage, the current discussions at IMO could be extended to the performance of ship’s structures in collisions and groundings.
Traditionally, IMO and various maritime administrations have not developed structural standards. Instead, they have relied on classification societies to develop such standards. The recent Common Scantling Rules developed by the International Association of Classification Societies (IACS) have resulted in new structural design codes for tankers and bulk carriers. The development of these common rules clearly shows the tendency of moving towards limit state design. Therefore, a logical future step should be to consider also the most important Accidental Limit States (ALS), including collisions and groundings, in these Common Structural Rules.