Question 40

The Correct Answer is B. **Explanation for B (Correct Answer):** Option B depicts a topmark of two black spheres, one above the other. According to the International Association of Marine Aids to Navigation and Lighthouse Authorities (IALA) maritime buoyage system (specifically System A and B, which share the same isolated danger mark), this topmark identifies an **Isolated Danger Mark**. An isolated danger is a small area, such as a wreck or a rock, which has navigable water all around it but is too deep or far from the main channel to be marked by a lateral buoy. The mark is typically black with one or more red horizontal bands. **Explanation for Incorrect Options:** * **A:** Option A shows a topmark of two black cones, points meeting at the center (a 'diamond' shape). This identifies an **East Cardinal Mark**, indicating that the navigable water is to the east of the mark. * **C:** Option C shows a topmark of two black cones, points downward. This identifies a **South Cardinal Mark**, indicating that the navigable water is to the south of the mark. * **D:** Option D shows a topmark of a single red sphere. This identifies a **Safe Water Mark** (or Mid-channel Mark), indicating that the surrounding water is navigable and the mark should generally be passed close aboard (it does not denote a specific danger).