When should a vessel sound a continuous bell signal according to the navigation rules?

A vessel should sound a continuous bell signal when navigating in fog as a means of signaling its presence to other vessels in the vicinity. The use of sound signals is crucial to ensure safe navigation in low visibility conditions, such as fog, where visual cues are limited. The continuous bell indicates that the vessel is either at anchor or is approaching a situation where communication of its status is necessary for the safety of all marine traffic. This sound signal helps to prevent collisions by making the presence of the vessel known to others that might be navigating nearby.

In scenarios like approaching a dock or when anchored in a congested area, sound signals may vary. For instance, vessels nearing a dock typically use a different set of sound signals to communicate their intentions, while being anchored does not necessarily require a bell signal unless in a congested area. The situation of another vessel approaching from behind would also not warrant a continuous bell sound but might call for different signals to indicate actions like maneuvering or giving way.