What kind of buoy would you use to denote a safe passage?

The can buoy is the correct choice for denoting a safe passage. Can buoys are typically used in navigational systems to mark channel edges or indicate safe areas for vessels to navigate through. They are usually cylindrical in shape and painted green, which aligns with the IALA (International Association of Lighthouse Authorities) system for buoyage.

In this context, their role is to guide mariners safely through hazardous or shallow areas by indicating where the safe water is located. Thus, the presence of a can buoy signifies a safe passage or channel for boats to follow.

In contrast, other types of buoys serve different purposes. Flashing buoys, for instance, often provide indication of hazards or specific locations but are not solely dedicated to marking safe navigation. Nun buoys, while they also mark channels, typically have a conical shape and indicate the port side of a channel as vessels approach from the sea. Bell buoys are used to signal areas of danger or mark certain positions but do not specifically denote safe passage. Each buoy type plays a specific role in maritime navigation, with the can buoy directly indicating safe channels for vessels.