## 1 Introduction  
Nowadays, the safest and most reliable way to combat the greenhouse effect is the one that goes through renewable energies. The main objective is to replace the current energy model, which is fundamentally based on fossil fuels, with energy from clean and renewable sources to reduce the carbon footprint [1, 2]. In this sense, notable advancements are being made in all the renewable energy production forms and particularly in photovoltaic and wind energy, both onshore and offshore [3, 4, 5, 6]. In particular for offshore wind energy, it is vital to take advantage of the potential energy available by locating the turbines in regions with stronger and more consistent winds. Normally, these conditions occur in deep waters. In these scenarios [3], the employment of floating offshore wind turbines (FOWTs) is more suitable and cost-effective in respect to the fixed structures. Currently, several prototypes or demo projects have been installed worldwide and have demonstrated the viability of different floating structures solutions (e.g., spar, semi-submersible, and tension leg platforms). For instance, the Hywind Scotland Pilot Project, installed in 2017, was the first pre-commercial floating wind park with five large turbines of 6 MW in array formation. Wind Float Atlantic was the second pilot project, with turbines of 8.4 MW--the largest ever installed on a floating platform [7]. The current and forecasted growth of the FOW sector drives the need to develop reliable and dependable station-keeping systems. In this regard, this technology continues to be the subject of importance to deep research aimed at reducing its operating and, mainly,maintenance costs toward improving its economic competitiveness and ensuring a safe working environment. Therefore, these systems must be capable of enduring all damage and degradation mechanisms that can be derived from the environment: corrosion, marine growth, harsh conditions (storms), etc. This requirement leads to getting significant efforts underway to develop more effective and efficient methods of inspecting and monitoring mooring lines to detect early stage signs of degradation and to predict failure. The first aspect is carried out by regular in-service inspections of mooring systems as part of the integrity management program. However, this methodology is generally costly and redundant; offshore inspection requires support vessels, crew, and equipment at a substantial daily rate. In contrast, the monitoring techniques provide the necessary information and the required periodic measurements to assist the structural-health monitoring (SHM) system in the tasks of extracting the fault-sensitive features from the measured signals and using them to analyze the system's condition [8]. The foremost mooring-line monitoring technologies include sonar probes, inclinometers, load cells, and fiberoptic sensors [9; 10; 11]. Some authors have also suggested ultrasonic guided waves and acoustic emissions as potential solutions. However, each one of these techniques has serious drawbacks that need to be tackled. The low reliability, accuracy, and robustness, and the limited load range of the load cells or the calibration difficulty to relate angle and mooring-line load in inclinometers or the expensive fiber optic technology are some examples of these disadvantages. Instead, mooring-line failure detection based on positioning systems is an attractive alternative with several advantages, such as (i) being highly cost effective, with minimum hardware and installation costs, (ii) having sensors located in safe areas, and (iii) requiring no wireless transmissions. The basic idea of this technology is to compare the measured position with the predicted position, which is based both on current meteorology and oceanography conditions, and the position offset is related to line damage [12].