How must vessels signal in case of restricted visibility as per Rule 35?

In situations of restricted visibility, vessels are required to use sound signals at regular intervals as specified in Rule 35 of the COLREGs. This regulation is designed to ensure that vessels can communicate their presence and navigate safely in conditions where visibility is significantly reduced, such as in fog, heavy rain, or darkness.

Sound signals are critical in these circumstances because they travel beyond visual range and can help prevent collisions. Each vessel type has designated sound signals it must use, and these signals serve to alert surrounding vessels to its presence, intentions, and movements.

While light signals can also play a role in communication, they are not specified in Rule 35 for restricted visibility scenarios. Displaying colored flags is not applicable for signaling in restricted visibility, and distress signals are reserved for emergencies, not routine rights of way or navigational communications. Therefore, utilizing sound signals is the appropriate method for vessels to maintain awareness and safety when visibility is compromised.