The growing demand for renewable energy has positioned Floating Offshore Wind Turbines (FOWTs) as a promising solution for harnessing wind energy in deeper waters. Unlike fixed foundation turbines, which are limited to depths of around 50 metres, FOWTs can operate in greater depths. However, this relatively new industry faces numerous challenges, with high costs currently limiting its large-scale deployment. While chains are widely used in mooring systems for the Oil & Gas industry, their required size and supply constraints for floating wind applications have made fibre ropes an attractive alternative. This thesis identifies several factors influencing the use of top chain in a hybrid mooring system, with a primary focus on determining the minimum required length for hook-up operations of semi-submersible FOWTs.

The relationship between the connection height of the top chain to the FOWT and the required top chain length, as well as the relationship between sea state variations and top chain length, were investigated through numerical simulations. Complications related to the depth below the sea surface, fibre elongation behaviour, and the overall performance of hybrid mooring systems were reviewed through existing literature. The dynamic behaviour of the top chain during the hook-up operation was analysed using OrcaFlex, with simulations performed in both frequency and time domains.

Dynamic analyses primarily focused on a dry chain link connection method, revealing that top chain lengths between 61 and 76 metres are required during hook-up operations. These lengths depend on wave conditions, connection height, and the installation vessel. The results showed that the required top chain length increases with wave height and period, while the length itself minimally influences its dynamic behaviour. For the lower segment of the mooring line, at least 10 metres of chain are required to prevent contact between the line and the rudders and thrusters of the installation vessel.

The study concludes that the top chain experiences minimal dynamic tensions relative to the static tension during hook-up, provided it includes sufficient sag and submersion. A bottom connection height offers the most benefits but necessitates a longer top chain during hook-up compared to a middle connection height. While fibre materials show promise as alternatives to chains, further investigation is required for their use in shallow waters. The dry chain link method is considered financially advantageous but it is expected to require the longest top chain length for hook-up operations compared to other methods. An in-depth analysis of applying pre-stretch to a 3-line mooring system is recommended to verify this assumption. These findings contribute to enhancing the economic feasibility of floating wind energy solutions, particularly for large-scale deployment.