Question 24 AB01 - Able Seafarer

The Correct Answer is D A lighted safe water mark is designed to indicate that there is navigable water all around the mark (e.g., mid-channel or landfall). To aid in its identification during daylight hours, it is fitted with a distinctive topmark. According to the IALA (International Association of Marine Aids to Navigation and Lighthouse Authorities) Maritime Buoyage System, **safe water marks are distinguished by having a single red sphere (spherical topmark)**. This topmark sits atop the mark and is highly visible. Here is why the other options are incorrect: * **A) A red and white octagon:** Buoys or marks are generally identified by shapes (cylinder, cone, sphere) or colors, not a specific geometric shape like an octagon. Octagonal shapes are not standard distinguishing features in the IALA system for this type of mark. * **B) Red and white retroreflective material:** Safe water marks are colored red and white stripes, and they often use retroreflective material to enhance visibility at night under searchlight. However, the retroreflective material *aids* visibility generally; it is the **spherical topmark** that is the specific primary identifier fitted to the mark to establish its *function* (safe water) during the day, regardless of whether it is lighted or not. * **C) A sequential number:** While buoys are often labeled, the number or letter is used for charting and specific identification within a waterway, not as the primary characteristic that identifies the **category** (safe water) of the mark. The unique identification feature for a safe water mark's purpose is its topmark.