moor

To moor a vessel is to hold it in position using anchors, lines, or both, rather than relying on propulsion. A moored ship remains stationary relative to the seabed or a fixed structure, regardless of tide, current, or wind direction within safe limits. This is distinct from anchoring alone, which typically uses a single anchor and chain; mooring often involves multiple point attachments and is intended for longer stationary periods or higher holding security.

Moorings fall into two main categories: anchor moorings, which use one or more anchors with chain or rope to the seabed, and fixed moorings, which attach to permanent installations such as bollards, pilings, buoys, or quay structures via lines or cables. A ship moored to a dock or pier uses springs, breast lines, and stern lines; a ship moored in open water may use multiple anchors deployed in a pattern to resist directional forces. The number and weight of anchors, plus the length and composition of ground tackle, depend on water depth, holding ground, vessel displacement, and expected weather exposure.

Common holding grounds and failure modes

Success in mooring depends heavily on bottom composition. Sand and mud provide good holding; clay is excellent. Rock, shale, or hard pan offer poor holding unless anchor flukes can find ledges or crevices. Organics and silt are unreliable. An anchor may drag if ground tackle is undersized, if holding ground is poor, if wind or current exceeds design parameters, or if line or chain has parted. Dragging is both a navigational hazard and a financial liability; the vessel owner is responsible for damage caused by a drifting moored ship.

Swinging room is critical in open-water moorings. A vessel on a single anchor swings in a circle with radius equal to the scope, the ratio of deployed chain or rope length to water depth. Insufficient swinging room increases collision risk with nearby vessels or hazards. This is why designated mooring fields exist in harbors, where swinging circles are pre-calculated and vessels are assigned specific positions.

The term moor comes from Middle English and Old English mor, related to Germanic roots meaning fen or bog. The metaphorical shift to securing a vessel likely reflects the image of tying something firmly to resistant ground, though the exact semantic path is obscure. In maritime usage, mooring is also used as a noun to mean either the act itself or the physical installation of anchors and lines used to hold a vessel.