Question 33 OSV02 - Mate - Offshore Supply Vessels

The Correct Answer is B **Explanation for Option B (67.5°):** Option B (67.5°) is correct because it aligns with the rules specified in the International Regulations for Preventing Collisions at Sea (COLREGs) and the corresponding Inland Rules (which generally mirror the International standard for navigation lights). * Rule 21 defines the characteristics of lights. * A **Stern Light** is defined as an all-round white light placed as nearly as practicable at the stern, showing an unbroken light over an arc of the horizon of **135 degrees** and positioned to show the light from dead astern to **67.5 degrees** on each side of the vessel. * $67.5^\circ$ (starboard side) + $67.5^\circ$ (port side) + $0^\circ$ (dead astern) = $135^\circ$ total arc. **Why the other options are incorrect:** * **A) 22.5°:** This is the angle of overlap between a sidelight and the masthead light (or the angle that the sidelights *must* show forward of the beam), but it is not the arc for the stern light on one side. * **C) 112.5°:** This is the required arc of visibility for a **Sidelight** (from dead ahead to $112.5^\circ$ aft on its respective side) or the arc for the **Masthead Light** (from dead ahead to $112.5^\circ$ aft on each side). It is the total arc for a sidelight, not the half-arc for a stern light. * **D) 135.0°:** This is the **total** arc of visibility for the stern light (from port to starboard). The question asks for the degrees shown **on each side** of the stern.