When should the fog signal of a manned vessel under tow be sounded?

The correct answer is that the fog signal of a manned vessel under tow should be sounded after the towing vessel's fog signal. This is in accordance with the International Regulations for Preventing Collisions at Sea. The purpose of this sequence is to ensure clarity in communication between vessels and establish the position of the tow in relation to the towing vessel.

By sounding the fog signal of the manned vessel after the towing vessel’s fog signal, you maintain a clear and recognizable sequence that helps other vessels understand which sounds correspond to which vessels. This is particularly important in reducing the risk of collisions in conditions of low visibility like fog, where sound is the primary means of navigation awareness.

In contrast, if the manned vessel were to sound its fog signal simultaneously with or before the towing vessel, it could lead to confusion for nearby vessels trying to determine the positions and movements of both the towing vessel and the towed vessel. Additionally, sounding it only if requested by the towing vessel would not comply with the regulations designed to enhance safety, as it is important for the manned vessel to sound its signal as part of standard procedures in poor visibility.