Ship hazards are dangers that can be encountered while sailing, such as reefs, icebergs, and shoals. A REEF is a ridge of rocks or coral that lies just below the surface of the water, making it difficult to navigate around. An iceberg is a large mass of ice that floats in the ocean and can cause damage to ships if they come into contact with it. A SHOAL is a shallow area of the sea, which can cause a ship to run aground if it is not navigated around.