A ship's anchorage is a point at sea where it may lower its anchor. Anchorages are locations where anchors are lowered and used, whereas moorings are often connected to buoys or something similar. The places generally feature circumstances conducive to secure mooring as well as protection from weather and other risks. Many anchorages are near islands that function as protective barriers against high seas and strong winds. Anchorages can be divided up into two general types: natural anchorages and man-made anchorages. Natural anchorages include beaches, jetties, and reefs. Man-made anchorages include buildings, ships, and even oil platforms. The type of anchorage will determine what kind of anchor is required. For example, if the anchorage is composed of very smooth rocks, then a rock anchor should be used instead of a chain or cable anchor. On the other hand, if the place is a sandy beach with waves over 3 meters (10 feet) high, a grommeted steel cable with a solid ball at each end would be appropriate. The depth of water around an anchorage is important because anchors need to be able to sink down through the surface of the water to the bottom without breaking apart under their own weight. If the water is too deep, they will not be effective. On shallow waters, anchor chains could be dangerous because they could drag across the surface and hurt someone.