If a towing vessel and her tow are severely restricted in their ability to deviate from their course, what additional lights must be displayed?

When a towing vessel and her tow are severely restricted in their ability to deviate from their course, they must exhibit additional lights in addition to the towing identification lights. This is essential for ensuring that other vessels can clearly and accurately identify the status of the towing vessel and understand its limitations in maneuverability.

The requirement for additional lighting serves to enhance the visibility and acknowledgment of the towing situation to other vessels, especially during periods of reduced visibility or nighttime operations. This is in accordance with the International Regulations for Preventing Collisions at Sea (COLREGs), which emphasize the need for vessels that are constrained by their draft or conducting tow operations to show their status clearly to prevent accidents.

Simply displaying navigation lights or towing identification lights does not adequately convey the constraints experienced by the towing vessel, which is why additional lights are mandated. The combination of these lights informs approaching vessels that they must exercise caution and give way, as the towing vessel may not be able to maneuver out of the way.