Mooring | Materials | Application | Program | Links | ||||
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Many semi-subs are anchor moored. Max operating depth with steel chain anchor lines is roughly around 3000m. This is limited due to decrease in restoring efficiency and horizontal stiffness of the line due to the large portion of strength required to overcome its own weight.
In recent years many rigs are being deployed with synthetic mooring lines. These lines, such as polyester and dyneema, offer the same strength for a 1/10th of the weight. This allows for smaller rigs to engage in operations in much deeper waters than previously thought possible. Utilizing synthetic materials allows a rig to be moored with a taut leg system. Here the restoring force is gained from the mooring lines, as opposed to a catenary system, where the restoring force is gained from the mooring line weight.
With synthetic lines the industry has switched to using suction piles. These can withstand higher uplift angles which reduces the spread radius and thus the watch circle. |
Taut and catenary mooring lines
Suction anchors for a preset mooring system |
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Inert Catenary
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Examples | ||||||||
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FPSO
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