As offshore wind turbines (OWTs) grow in size and are installed in deeper waters, the use of traditional jack-up vessels for installation faces increasing limitations. Semi-submersible crane vessels (SSCVs) offer a promising alternative; however, their floating nature introduces complex dynamic behaviour that can adversely affect installation operability. This thesis investigates the operability of single blade installation using an SSCV.


A numerical model was developed in OrcaFlex to simulate the relative dynamic behaviour between the hub of a bottom-fixed 15 MW OWT and the root of a suspended blade on an SSCV, during the alignment phase of the blade installation. The analysis focuses on the Thialf, an SSCV from the Heerema Marine Contractors fleet.


The relative motions of the OWT hub and blade root were assessed through modal and time domain analyses under environmental conditions representative of a Baltic Sea site. Results show that wave induced motions dominate the system’s dynamic response. Hub motions were strongly amplified when wave peak periods approached the natural frequency of the turbine, while blade root dynamics were governed primarily by vessel motion and the coupling between vessel response and the pendulum behaviour of the suspended blade.


Sensitivity analyses demonstrated that operational parameters, including vessel draught, suspension length, and tugger configuration, significantly affect the system’s dynamic behaviour.


Operability was evaluated using limiting criteria consisting of a maximum displacement threshold and a maximum outcrossing frequency. The analysis revealed that operability is restricted under conditions of hub resonance, vessel resonance, or coupling between the vessel and the pendulum behaviour of the suspended blade, and that the choice of limiting criteria strongly influences the overall operability.


SSCVs can perform comparably to jack-up vessels in moderate sea states, where vessel motions remain limited. In more demanding conditions, however, amplified dynamics and resonant responses may induce excessive motions that render the installation inoperable. The applicability of SSCVs for OWT installation must therefore be evaluated with respect to both site specific environmental conditions and the operational configuration. With careful tuning of the installation setup, SSCVs can provide a viable alternative under favourable conditions.