To determine the probability of grounding another mathematical model needs to be developed and similar risk control options studied. The procedure should include power grounding where the ship is running on a ground with forward speed but also drift grounding for disabled ships.
Models for calculation of the grounding probability Pg could be developed in a way similar to the method described above for ship–ship collisions, see Otto et al. [31]. The difference is that an obstacle, for example a rock, on which the ship grounds, is fixed in its position and that it is in most cases below the water surface. See Fig. 10.
Again ship traffic data needs to be collected for the number of ships and the spatial distribution in the vicinity of the most important coast lines, and a procedure should be developed for characterisation of these coast lines, i.e. distribution of rocks, bottom profile data, tide variations etc. As indicated in Fig. 10, for calculation of the probability of collision with an offshore structure and/or grounding, the collision model based on Eqs. (2) and (3) has to be augmented by an additional category of accident related to the probability that the vessel does not change course at bends on the shipping route, see Eq. (4), together with further categories related to drifting vessels due to steering machine failure or engine blackout. See [26] and [32].
Based on the principles for estimation of collision probabilities described above some procedures have been developed for calculation of collision probabilities in specific waterways where the ship traffic distribution is known. One such published procedure is the GRACAT software (Grounding and Collision Analysis Toolbox), see Friis-Hansen and Cerup-Simonsen [33].
Unfortunately, there are very few published procedures for calculation of the probability of grounding. This is an area in need for further research.
Possible risk control options related to reduction of the frequency of grounding events are similar to those given above for reduction of the probability of ship–ship collisions and contacts. Of course, the Electronic Chart Display and Information System (ECDIS) will mainly be effective in preventing grounding if it makes use of Electric Navigational Charts (ENC).