Method for inspection of catenary anchor lines connected to a floating object

A method for measuring a line angle of at least one mooring line connected to a floating object, the floating object floating in a body of water, the mooring line being connected between the floating object and an anchoring body disposed in a bed of the body of water, in which the floating object is coupled to the mooring line by a line connector;

• the method comprising:
• defining at least three data points each associated with a respective location on the mooring line;
• on said at least three data points obtaining a respective value associated with the location on the mooring line;
• determining parameters of an equation describing an anchor line curve from the obtained values associated with the location on the mooring line for said at least three data points;
• calculating at a predetermined position on the mooring line a line angle of the mooring line from a derivative of the equation of the anchor line curve at the predetermined position based on the determined parameters,
• wherein the method further comprises:
• providing a group of sensors, comprising at least three sensors, each of the sensors configured for measuring the respective value associated with the mooring line on one of the at least three data points and for transmitting a signal of said measured value,
• wherein a first position sensor from the group of sensors is positioned on the floating object and comprises a GPS sensor;
• the method further comprising:
• determining a location of the center of an articulation of the line connector from the position of the first position sensor as a value of a first data point, and
• wherein a second sensor and a third sensor each comprise an ultra-short baseline, USBL, transponder, and are positioned at a respective second and third location on the mooring line, at least the second sensor being a position sensor and the values measured by the position sensor being associated with the respective location of the respective position sensor;
• wherein at least the second sensor and the third sensor are installed on predetermined locations on the mooring line by a remotely operated underwater vehicle, ROV, and
• the step of obtaining the values on the at least three data points comprises receiving from each associated sensor the signal of the respective measured value, and associating for each received signal the measured value with the location of the data point on the mooring line, wherein the location of the second sensor and of the third sensor, if the third sensor is a position sensor, is determined by:
• in response to a transmission by a USBL transceiver, receiving the measured signals from the respective USBL transponder by said USBL transceiver, the USBL transceiver being at a remote location,
• determining coordinates of the position of the second and third position sensors from the respective measured signal such that the coordinates of the second and third sensors are each referenced to a location of the USBL transceiver.