Offshore Catenary Mooring Line Tension & Profile Calculator

A catenary mooring line relies on the weight of heavy chain hanging in a natural catenary curve to provide restoring horizontal stationkeeping forces as a floating vessel drifts.

The line lifts off the seabed when the vessel surges away, generating an increasing horizontal restoring force without requiring mechanical winching.

The catenary parameter a = H / w represents the radius of curvature at the lowest horizontal point.

Maximum tension always occurs at the highest elevation (the vessel fairlead): Tmax = H + w·h.

The grounded portion lying on the seabed acts purely horizontally on the drag-embedment anchor.

Suspended length s indicates the minimum line length required before the anchor experiences vertical uplift.

Touchdown distance gives the horizontal location where chain contacts the seafloor.

• Chain weight: Heavier chain provides stiffer restoring force but increases platform vertical payload payload.
• Water depth: In ultra-deepwater (> 1,000 m), heavy catenary chains become inefficient, requiring taut synthetic polyester rope systems.

• Stationkeeping design for drilling semi-submersibles and production FPSOs.
• Mooring line tension checks per API RP 2SK and DNV-OS-E301.

• Assumes flat horizontal seabed and homogeneous line without clump weights or buoyancy buoys.