Question 117Navigation General

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Which topmark shown in illustration D023NG below identifies an isolated danger?

Diagram for USCG Navigation General: Which topmark shown in illustration D023NG below identifies an isolated danger?
A A
B B
C C
D D
AI Explanation

The correct answer is B. The topmark shown in illustration D023NG that identifies an isolated danger is a single black sphere. This is in accordance with the International Association of Lighthouse Authorities (IALA) Maritime Buoyage System, which specifies that an isolated danger mark should display a single black sphere as the topmark. The other answer choices do not correctly identify the topmark for an isolated danger mark. A, C, and D represent different topmarks used for other types of navigational marks, such as cardinal marks or safe water marks, but not for isolated danger marks.

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