Question 332Navigation General

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In both regions of the IALA buoyage system, which topmark shown in illustration D022NG below is used on a special mark?

Diagram for USCG Navigation General: In both regions of the IALA buoyage system, which topmark shown in illustration...
A A
B B
C C
D D
AI Explanation

The correct answer is D. The IALA buoyage system (International Association of Marine Aids to Navigation and Lighthouse Authorities) specifies that a special mark, which is used to indicate a feature or location that is not a channel, must have a topmark in the shape of a single yellow X, as shown in illustration D022NG. This topmark configuration (option D) is the one used on special marks in both regions of the IALA system. The other options are incorrect because they do not match the topmark required for special marks under the IALA guidelines. Option A shows a single sphere, option B shows two cones, and option C shows a single cone - none of which are the correct X-shaped topmark for special marks.

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Official Resources
USCG Navigation Rules (COLREGS) 33 CFR Navigation Rules USCG National Maritime Center
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