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How are isolated-danger buoys marked to show safe water on all sides?

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lighthouse Lighthouse at Portsmouth, New Hampshire.

Isolated-danger buoys are specifically designed to mark a hazard that has navigable water on all sides. These buoys are identified by the following characteristics:

Coloring: They are painted with alternating horizontal red and black bands.1
Topmark: They carry two black spheres, one positioned above the other.1

These markings allow mariners to identify the danger and safely navigate around the buoy in any direction.12