Since the exploitation of wind as a renewable energy resource, jack-up vessels equipped with more than three independent legs are increasingly employed to transport and install the components of offshore wind turbines. By lowering the movable legs the vessel is able to elevate the hull from sea water level. In elevated position the vessel provides a stable platform to perform installation activities. The legs are equipped with spudcans which serve as foundation of the vessel. The elevating process consists of a preload phase to ensure sufficient capacity to withstand operational and possible storm conditions. The preloading of four-legged jack-ups is performed by alternately applying vertical loads on diagonally opposite leg pairs, up to achieving a stable condition in which nearly constant load levels can be held by each leg. The aim of this research is to develop a 3D model to asses the preload duration of the jack-up vessel Aeolus in cohesive soil. The viscous behaviour of cohesive soil, like clay, influence the acting leg load during preload of the jack-up vessel. The shear strength of clay is a function of strain rate meaning that resistance increases due to viscous effects with increasing penetration rate. During spudcan penetration the shearing resistance is high but will reduce significantly when penetration is stopped as the viscoplastic resistance diminishes. Together with the onset of isotach soil behaviour this causes the loads to redistribute between the legs occurs. In this study it is assumed that sufficient preloading is achieved when the leg load reduction is limited to 400 ton / 15 min. To satisfy this criterionmultiple load cycles of each leg pair are performed. Site specific geotechnical data and information on the structural stiffness of the Aeolus have been available for this research and allowed for an accurate analysis of the processes during the preload procedure. The Soft Soil Creep (SSC) model is used as constitutive model and accounts for viscous effects by formulating irreversible strains by means of viscoplasticity. The soil at the project site is classified and the constitutive model is calibrated based upon the available soil test results. The structural behaviour of the vessel is captured via a simplified beam configuration representing the deck structure and legs, the stiffness of the beams is verified using the results from a so-called predrive analysis. The extension of the legs is established bymeans of negatively pre-stressed node-to-node anchors. Simulations of a single spudcan penetrating at various depths and penetration rates are performed to identify the extent of viscous strain rate effects fromthe results. With the developed 3D model Small Deformation Finite Element analyses of the preload procedure are performed. The leg loads and penetrations are monitored and compared to jacking data fromthe actual project site. The processes in the soil and structure are analysed and the influence on the preload procedure and preload duration is identified. For both type of simulations six different case-calculations are performed addressing variation in the initial spudcan depth, the OCR, the penetration rate, the permeability and the type of preload procedure. The simulations indicated that the penetration of a spudcan influences the penetration of an adjacent spudcan, this reciprocal influence of the spudcans emphasizes the importance of onemodel comprising all spudcans in the same 3D soil domain. The developed model slightly overestimates the spudcan penetration and underestimates the total preload duration. Simulations of the overshooting preload procedure and an alternative preload procedure are performed with the FE model. For the soil conditions used in this research, both the overshooting and the alternative procedure are effective in reducing the number of preload cycles to satisfy the preload criterion. Compared to the normal preload procedure, it is expected the overshooting procedure improves the preload duration. For the alternative procedure however, the duration of a preload cycle increases significantly and consequently the procedure does not improve the preload duration. Using a lower spudcan penetration rate during the normal preload procedure is also effective in reducing the number of preload cycles but significantly increases the elapsed time to complete the preload procedure. The above conclusions have been made on the basis of the model results, which is calibrated for the soil conditions at the specific project site.