Introduction
Objectives
The primary objective of this site is to describe the theoretical foundation for the collision and grounding frequency analysis so that interested user of IWRAP MK II may understand the basic theory behind the program.
It is assumed that the reader assumes a level of mathematical and probabilistic skills to gain full benefit of this site.
History
During the period 1998 to 2001, state-of-the-art software for grounding and collision analysis was developed within the ISESO_Project at the Technical University of Denmark.
The ISESO_Project was followed by a project named BaSSy. IWRAP MK II constitutes a reduced version of the collision and grounding analysis program, the BaSSy ToolBox (GRISK), developed through the BaSSy_Project.
The page History of IWRAP gives a more thorough description of how IWRAP has developed over time.
Risk Model
To quantify the risks involved with vessel traffic in specified geographical areas, rational criteria for prediction and evaluation of grounding and collision accidents have to be developed.
This implies in principle that probabilities as well as the inherent consequences have to be analysed and assessed.
This site (IWRAP) not only defines the theoretical background for the collision and grounding analysis, but it also summarises and discusses the background for the so-called causation probability.
A method for evaluating the collision and grounding frequency of vessels operating on a specified route is outlined.
In order to identify the frequency of experiencing any collision or grounding in a given area involves first a specification of the routes and the associated traffic on the routes.
Subsequently, the collision and ground frequency may be obtained by looping over all vessels operating on the route.
| IWRAP MK II program calculates grounding and collision frequencies, it does not include the consequence analysis. |
One of the benefits of the formulated procedure is that it allows comparisons of various navigational routes by assessing the relative frequencies of collisions.
Causation Probability
The applied model for calculating the frequency of grounding or collision accident involves the use of a so-called causation probability, that is multiplied onto a theoretically obtained number of grounding or collision candidates.
| The causation factor models the probability of the officer on the watch not reacting in time given that he is on collision course with another vessel (or alternatively on grounding course). |
The numerical value of the causation probability is not a unified value but often varies for different geographical locations.
The applied value of the causation probability is therefore typically adjusted by a calibration to registered data.
On the basis of a literature search the present document summarises some of the causation probabilities that have been applied in different studies.
Some of the factors that are of importance when assessing the causation probability are also identified.
Bayesian Network for ship-ship collision
Moreover, a Bayesian Network model for ship-ship collision is formulated for an analytical estimation of the causation probability.
The obtained result agrees well with that obtained from statistical analyses of data.
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Source: IWRAP Mk II, Basic Modelling Principles for Prediction of Collision and Grounding Frequencies, (draft working document), Rev. 4, 2008.03.09, Peter Friis-Hansen, Technical University of Denmark. |