What is the purpose of an all-around light on an anchored vessel greater than 100m?

The purpose of an all-around light on an anchored vessel greater than 100 meters is to indicate that the vessel is anchored. According to the COLREGs, vessels of this size must display an all-around white light to ensure they are visible to other vessels in the vicinity, particularly at night or in low visibility conditions. This light serves as a navigational aid, signaling to other mariners that the vessel is not in motion and is secured in a stationary position. This is crucial for maritime safety, as it helps prevent collisions and allows other vessels to navigate safely around the anchored ship.

The other options do not align with the intended function of the all-around light. While signaling for help, notifying about navigation hazards, or visual decoration might have their own contexts in maritime operations, they do not apply to the specific requirement of indicating that the vessel is at anchor.