Another mooring used is the concrete sinker. These are used when a jetting cone can't be jetted far enough into the river bottom. The biggest cause of this are rocks. The sinkers are dumped over the side. In some areas chain is used in place of the wire-rope. This is usually where the wire-rope wears out quickly. If a buoy is set with a chain moor, a concrete sinker must be used instead of the jetting cone.