What type of sound signal does a towing vessel use in a situation where it is constrained by its draft?

In situations where a towing vessel is constrained by its draft, it is required to signal its presence and intentions to other vessels. The correct sound signal in this case is one prolonged blast followed by two short blasts.

This specific combination of sound signals is established in the International Regulations for Preventing Collisions at Sea (COLREGs) and serves to communicate effectively with other vessels. The prolonged blast indicates that the towing vessel is making its position known, while the two short blasts signify that it is constrained by its draft and may not be able to maneuver as freely as other vessels. This is critically important for navigation safety, as it alerts nearby vessels to take caution and be aware of the towing vessel's limited ability to change course or speed.

In this scenario, other sound signals do not convey the same information required for a towing vessel in this specific situation. Thus, the use of one prolonged blast followed by two short blasts is necessary to ensure that the navigating situation is clearly understood by other mariners.