In poor holding ground, only the weight of an anchor matters in good holding ground, it is able to dig in, and the holding power can be significantly higher. An anchorage location may be chosen for its holding ground. Holding ground may be fouled with obstacles. Some bottom materials hold better than others for instance, hard sand holds well, shell very poorly. Different types of anchor are designed to hold in different types of holding ground. Holding ground is the area of sea floor which holds an anchor, and thus the attached ship or boat. The ratio of the length of rode to the water depth is known as the scope (see below).
The vessel is attached to the anchor by the rode (also called a cable or a warp) It can be made of rope, chain or a combination of rope and chain. Modern anchors for smaller vessels have metal flukes which hook on to rocks on the bottom or bury themselves in soft seabed. Semi-permanent mooring anchors (such as mushroom anchors) and large ship's anchors derive a significant portion of their holding power from their mass, while also hooking or embedding in the bottom. Permanent moorings use large masses (commonly a block or slab of concrete) resting on the seabed. Anchors achieve holding power either by "hooking" into the seabed, or mass, or a combination of the two.
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