Not Under Command (NUC)

A ship that, due to exceptional circumstances, is unable to manoeuvre as required by the International Regulations for Preventing Collisions at Sea (COLREGs) and therefore cannot keep out of the way of other vessels.

A vessel that is “Not Under Command” (NUC) is in a state where it cannot comply with the standard manoeuvring rules set forth in the COLREGs. This designation is outlined in Rule 3: General Definitions, part (f) and typically arises due to unforeseen or uncontrollable circumstances, such as a mechanical failure, loss of steering, or other critical issues that render the vessel incapable of responding to navigational commands. When a vessel is NUC, it is required to display specific signals to alert other mariners to its condition. These signals include two all-round red lights in a vertical line at night and two black balls in a vertical line during the day. The purpose of these signals is to ensure that other vessels in the vicinity are aware of the situation and can take appropriate action to avoid a collision or hazardous interaction. 

It is important to note that a vessel declaring itself NUC is not absolved of all responsibilities; it must still take reasonable measures to mitigate risks, such as anchoring if possible or using emergency propulsion. Additionally, other vessels are required to give way to a vessel displaying NUC signals, as it is considered to have restricted ability to manoeuvre. The concept of “Not Under Command” is distinct from “Restricted in Ability to Manoeuvre” (RAM), as the latter refers to vessels engaged in specific operations that limit their manoeuvrability, while NUC is typically due to an unexpected loss of control. Understanding and correctly responding to NUC signals is a fundamental aspect of safe navigation and adherence to maritime protocols.