Question 24 RVR01 - Master of Unlimited Tonnage

The Correct Answer is A. **Explanation for A:** Option A correctly identifies the arc of visibility for a red sidelight (port light) under both the International Regulations for Preventing Collisions at Sea (COLREGs) and the Inland Rules. The regulation (Rule 21, Definitions) specifies that sidelights must show an unbroken light over an arc of the horizon of **112.5 degrees** (or 10 points of the compass), fixed to show the light from right ahead to **22.5 degrees abaft the beam** on its respective side. In the provided illustration (D023RR, which is standard navigation test material), arc 'A' typically represents this $112.5^\circ$ arc of visibility for the port (red) sidelight, starting from dead ahead and extending $22.5^\circ$ past the beam. **Explanation for Incorrect Options:** * **B is incorrect:** Option B typically represents the arc of visibility for the sternlight, which covers an arc of $135^\circ$ (or $67.5^\circ$ on each side of the stern) and does not cover the forward part of the vessel. * **C is incorrect:** Option C usually represents the arc of visibility for the masthead light (or steaming light), which covers an arc of $225^\circ$ (or $112.5^\circ$ on each side of dead ahead). This arc is too wide for a single sidelight. * **D is incorrect:** Option D typically represents the arc of visibility for the green sidelight (starboard light), which covers the same $112.5^\circ$ arc as the red light but on the opposite (starboard) side of the vessel.