Catenary                          


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The name catenary refers to the shape of the anchor lines. This is the shape of a line hanging freely between two points. This shape can be described by the catenary equation. For a description of these equations, take a look at [Catenary equation].

The mooring lines hang at the corners of the semi sub unit and terminate horizontally on the sea bed. As a consequence of this shape, this system has long mooring lines compared to the water depth. A catenary mooring system uses the weight of the anchor lines as restoring force. In the occasion that the semi sub unit experiences an offset, the suspended weight of the anchor line increases because of the increase in length of the anchor line, resulting in progressively stiffening characteristics. Since the lines hang more or less freely in the water, the length and therefore the weight of the anchor lines increase rapidly with water depth.

Mostly the mooring lines for a catenary mooring system consist of chain. In deeper water the chain is partially replaced by steel wire to save weight. However since semi subs have a relatively low payload, this holds that the catenary mooring system is limited to a certain water depth. Beyond this depth other systems or other materials should be considered.

Figure 2.2: Steel Catenary Mooring

 


 

       

                                                                     

 

 

 

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Last modified: 10/16/06