Which of the following is a method of calculating excursion?

Calculating excursion involves understanding the total horizontal distance that a vessel deviates from its intended track or course. The method that encompasses a systematic approach to this calculation is the fraction of the Water Current Ratio (WCR). This method accounts for the influence of currents on the vessel's path, enabling a precise assessment of how much the vessel may have strayed due to environmental factors.

Using the fraction of the WCR allows operators to quantify excursion in a standardized manner, which is especially relevant when navigating in areas where currents can significantly affect a vessel’s trajectory. This can enhance situational awareness and improve decision-making by providing data that can be compared against established parameters or thresholds.

While other methods like direct measurement, visual estimation, and GPS tracking may provide data relevant to a vessel's position and movement, they do not inherently focus on the calculation derived from the effect of environmental factors relative to the vessel’s intended course in the same structured way that the fraction of the WCR does. Therefore, choosing the fraction of the WCR as the method of calculating excursion is appropriate due to its analytical rigor in accounting for the dynamics of navigation.