29.1. Installation of Mooring Systems#
When looking at the requirements to ensure a robust installation method, the following aspects should be considered:
As discussed in session one, connection systems allow mooing lines to connect directly to the vessel hull and avoid winches on the vessel. This requires the use of In-line Mooring Tensioners and/or Pull-in Connectors.
The lay corridor needs to be surveyed and free of material.
During laying twist & snaking loss (snaking being movement outside of a straight line) needs to be reduced by keeping tension on the line while laying.
Pre-tension is required to reduce snaking loss and in the case of synthetic wires, to arrange pre-stretching to a defined level.
As an example, mooring chain twist may be limited to 0.5 degrees per link and/ or maximum 10 degrees over any 20 links and it good practice to lay out the chain before installing which ensures limited twist. The picture shows a chain laid out for the Prelude FLNG mooring.
Once laid, the position/ length is checked and cut-to-length can be performed, which ensures the line between anchor and fairlead has the length which was intended in the design.
Note
The moorings are often pre-installed, prepared for when the floater arrives to be hooked up. For pre-laying the mooring, sometimes Remote Operated Vehicles (ROV’s) are used: