When must a sailing vessel keep her course and speed?

A sailing vessel must keep her course and speed when being overtaken because the vessel being overtaken is the one that has the right of way according to the rules of the road. This is crucial since the overtaking vessel has the responsibility to maneuver safely around the other vessel. Maintaining course and speed ensures predictability and allows the overtaking vessel to assess the situation and make necessary adjustments safely.

In the context of sailing, the rules state that when a vessel is being overtaken, it does not alter its course or speed, allowing the overtaking vessel to navigate safely without conflicting with the actions of the sailing vessel. This adherence to maintaining speed and direction is essential to prevent accidents and ensure safe navigation in busy waters.

Other scenarios listed in the options do not impose the same obligation on a sailing vessel. For instance, while on a close haul, a sailing vessel might need to adjust her sails or course depending on wind conditions. In open waters, vessels are generally expected to be mindful of traffic but do not have an obligation related to overtake maneuvers. When anchored, a vessel has no obligation to maintain speed or course because it is no longer actively navigating.