In which situation would you NOT use Parallel Indexing?

Parallel indexing is a navigational technique used with radar to maintain a safe distance from navigational hazards or to follow a specific course while accounting for any lateral drift. This method relies heavily on having identifiable radar landmarks, as these are critical to establish a reliable reference point for tracking the vessel’s position relative to the planned path.

The correct choice is the situation where there are no identifiable radar landmarks. Without these landmarks, you cannot effectively apply parallel indexing as there would be no fixed points to measure your distance and course against. This would render the technique useless, as you would lack the necessary contextual information to monitor your position accurately.

In contrast, clear radar landmarks and heavy vessel traffic both provide conditions under which parallel indexing can be beneficial. Clear radar landmarks allow for precise calculations, while heavy traffic may necessitate the heightened situational awareness that parallel indexing provides. High visibility conditions, although they offer benefits for other navigation techniques, do not directly negate the use of parallel indexing but rather enhance it by making radar targets easier to identify.