Which of the following is considered a prohibited signal?

The selection of continuous sounding with fog-signalling apparatus as a prohibited signal aligns with maritime safety protocols. In the context of COLREGs (International Regulations for Preventing Collisions at Sea), specific signals are designated for particular situations to ensure clarity in communication among vessels and to avoid misunderstandings.

Continuous sounding with a fog-signalling apparatus can create confusion because it has a specific meaning in instances of low visibility, such as fog. It's important that vessels maintain a clear distinction between the different sound signals that communicate intentions or status. Continuous blasts could readily be interpreted in ways that are not intended, making it difficult for nearby vessels to ascertain the situation or the actions required to be taken, particularly in busy waterways.

On the other hand, signals like a single short blast, a series of rapid blasts, and a single long blast serve clear purposes under specific circumstances. For example, a single short blast indicates a vessel's intent to pass another vessel on its port side. Meanwhile, a single long blast generally denotes maneuverability or indicates the presence of a making-way vessel. Each of these sound signals is recognized and can be understood by other vessels in order to maintain safe operation and prevent collisions. The clarity of these signals is why they are permissible as opposed to continuous sounding