Navigation General · Aids to Navigation — Isolated Danger Mark
An isolated danger mark (black with red band, two black spheres topmark) indicates:
- ASafe water all around
- BAn anchorage
- CA traffic separation lane
- DA danger of limited extent with navigable water all around it✓ Correct
Explanation
An isolated danger mark is placed on or near a small hazard (e.g., a wreck or rock) that has navigable water on all sides. Its two-black-sphere topmark and black/red bands warn the mariner to give it a wide berth.
Authority: IALA Maritime Buoyage System
Practice the full Navigation General bank
Free spaced-repetition quizzing across 2190 USCG exam questions — it schedules your reviews so the ones you miss come back until they stick.
Related Navigation General questions
- Dead Reckoning
A vessel departs a known position at 0800 on course 090°T at 12 knots. What is the DR position at 1100?
- Time-Speed-Distance
Using the 60 D = S × T formula, how long will it take a vessel traveling at 15 knots to cover 45 nautical miles?
- Time-Speed-Distance
A vessel travels 90 nautical miles in 6 hours. What is the vessel's speed?
- Dead Reckoning
Which of the following is the best definition of a Dead Reckoning (DR) position?
- Set & Drift
A vessel steers 000°T at 10 knots for 2 hours. The observed position shows the vessel is 4 nm east of the DR position. What is the set and drift of the current?
- Set & Drift
A current has a set of 225°T and a drift of 2 knots. Over 3 hours, how far and in what direction will this current displace a vessel from its DR position?