Under what rule is the visibility of vessels determined?

Rule 5 and Rule 19 of the COLREGs address the concept of visibility in the context of navigation and avoiding collisions. Rule 5 emphasizes the importance of maintaining a proper look-out by sight and hearing as well as by all means available, which is crucial in determining visibility conditions and assessing the risk of collision. It requires vessels to be vigilant and aware of their surroundings, accommodating various visibility scenarios, such as fog, rain, or darkness.

On the other hand, Rule 19 specifically outlines the conduct of vessels in restricted visibility. This rule mandates that vessels navigate with extreme caution when visibility is impaired, indicating that they must take appropriate measures to avoid collisions when they cannot see other vessels. Hence, both rules work together to govern how vessels should operate under varying visibility conditions. Given this context, the option stating that visibility is encompassed within both Rule 5 and Rule 19 captures the comprehensive approach of the COLREGs towards navigating safely in different visibility situations.