Boat operators should have which of the following on board?

The correct answer is C. Nautical charts and related documents.

Nautical charts are essential for safe navigation, as they provide detailed information about waterways, including depths, hazards, and traffic routes. While the other options may be useful, having charts and related documents is a fundamental requirement for boat operators to ensure safe navigation. If you have any more questions or need further clarification, feel free to ask!