The correct answer is A) A dead reckoning (DR) plot should be started each time the vessel's position is fixed. A DR plot is used to estimate a vessel's position based on its course, speed, and time traveled since the last known position. It should be started or updated each time the vessel's position is fixed, either visually, by GPS, or by other means. This ensures the DR plot accurately reflects the current estimated position of the vessel. The other options are incorrect because: B) DR plots do not necessarily need to use magnetic courses, C) there is no requirement to replot the DR hourly, and D) while set and drift should be accounted for in the DR calculations, it is not a requirement that the DR plot itself must take set and drift into account.