Since the oil price collapse at the end of 2014, operators in the offshore industry experience a decline in revenues and a need for downsizing. Simultaneously, the wind industry is growing every year, as an increasing amount of companies and consumers are investing in green energy. This creates opportunities for Heerema Marine Contractors (HMC), as they have ample experience in offshore installations, operations and maintenance. Currently, in most cases a Jack-Up Vessel (JUV) is used to install offshore Wind Turbine Generators (WTGs). With the exception of Hywind, a wind farm of floating wind turbines commissioned with a Semi-Submersible Crane Vessel (SSCV) near shore and thereby protected from large waves, there is little experience in installing large WTGs with a floating vessel in offshore sea states. Current trends in Offshore Wind Farm (OWF) development are the upscaling of WTGs and installations in deeper waters, both resulting in more complex operations. In the current market however, there are many installation operators with lower priced JUVs. Therefore, to compete and make it economically viable for HMC to enter this industry, HMC must be able to install WTGs at a faster rate than the rate of conventional installation vessels. The main objective of this master thesis is to determine the economic and technical feasibility for HMC to enter the offshore wind industry as an installation operator. First, the attractiveness of the offshore wind market is analyzed. For the analysis of the offshore wind market as a business environment the theoretical framework ‘PESTLE’ is applied. Through the application of the ‘Porter’s Five Forces’ model, the competitive position of HMC as an potential entrant to the offshore wind market is analyzed. Second, insight is gained under which conditions it is economically feasible to use a SSCV for the installation of 10 MW WTGs. Different logistical methods are compared in terms of installation time and installation costs, as a function of site particularities, and by comparing the use of a JUV, a purpose-build installation vessel and a SSCV. As the installation of WTGs makes up a significant percentage of the total costs of a project, the workability of the installation vessel is of great importance. To address the technical feasibility, this thesis aims to quantify the influence of wave forecast on the workability of installing a fully-assembled 10 MW WTG with a SSCV. The offshore wind market in the North Sea as a business environment is evaluated to be attractive. Additionally, there is a large potential for building new OWFs in the North Sea and governmental support is significant and assumed to be stable in the future. The trends that OWF development moves into deeper waters and further offshore, as well as the increase in size of wind turbines are all positive for floating installation vessels with larger crane capacity, as many JUVs have reached their maximum capacities. Although the barriers to enter the OWE industry are high, the power of the OWF developers is significant and the price competition among installation operators is fierce, the threat of alternative WTGs becoming mainstream is small due to economies of scale and the enormous potential of new OWF development. It is recommended to enter the market with a HMC SSCV and focus on the installation of extra-large WTGs (≥10 MW) and thereby succeed in the offshore wind market by specialization. Based on the current ECN Tool (version 2.1) and the assumptions made, it is economically feasible to use an SSCV for the installation of completely pre-assembled wind turbines in a large OWF (>1500 MW). In the scenario used in the ECN Tool, the duration of the WTG lift, installation and the SSCV sailing to the next TP should be less than six hours. According to the industry, a great concern is the movement of the SSCV during the set-down, and thereby making it a complex operation with impact loads that are more difficult to predict. Wave forecasting is the key that can take away this concern, however it is still an ‘unproven innovation’ in the industry. With the use of a 2 minute wave and motion forecast, the waiting on weather for the ‘WTG lift’ and ‘WTG set-down’ on the TP can be reduced from 28 hours per turbine to 7 hours for the ‘WTG lift’ and 48 minutes for the ‘WTG set-down’. Subsequently, based on a 2 minute wave and motion forecast, the impact load on the bottom of the tower and the TP can be reduced by 13 % by choosing an optimal sea elevation for the set-down moment. As the average waiting on weather time is relative high for installing the third blade and lifting the WTG, it is furthermore recommended to investigate the influence on wave radar forecast on these steps. The implementation of wave radar technology during the installation process, is to be investigated further.

HeeremaMarine Contractors (HMC) owns and operates several semi-submersible crane vessels (SSCV) used for offshore heavy lift operations. Throughout the engineering phase of a (dual crane) heavy lift, dynamic lift models are generated by combining bodies with their hydrodynamic properties, inertia and spring-dashpot elements. The models represent the mass-spring system of a heavy lift over the different lift stages during a topside installation. These stages characterize the free floating, load transfer, free hanging and set down
phases.

Hook load fluctuations are governed by the relative vertical motion of the load and the crane boom tip. At the load transfer phase this motion is governed by both the motion of the vessel and the barge, whereas for the free hanging phase it is mostly effected by the motion of the vessel. To achieve safe and successful projects, an accurate prediction of the load and motion responses is essential while advising offshore personnel about the lift to perform. At the moment an inconsistency exists between predicted load fluctuations and offshore
crane measurements. This is the main reason for this research.

Until now a simplified spring-damper system is used to incorporate the hoist wire reeving system of a crane.This simplification is not fully justified and three goals are set up to model this in a more detailed manner. Firstly, the driving parameters of the load-crane-vessel system are assessed. Secondly the dynamic behavior of the wire reeving system is captured in a numerical model in Simulink. Finally, the dynamic load fluctuations of the model are compared with offshore measurements to both validate the model and analyze the results.

The dynamical model of the load-crane-vessel system is solved in the time domain and it consists of two parts. The first part considers the sheave and wire system of the crane. An equation of motion is derived for each sheave where dry friction is taken into account and leads to a stick-slip effect. This friction originates from the sheave bearings and from the bending friction of the steel wire rope that runs over it. When a load is raised, the stress in each rope part increases from the winch to the dead end. With a lowering operation the effect is the opposite. Due to stick-slip this force difference remains in the crane wires after the operation. The friction factors of the sheaves in the numerical model are tuned with steps observed in offshore load measurements during crane operations.

The second part of the model imposes the measured vessel motions to calculate the motion of both crane boom tips and the topside. This is performed by applying their influences as external forces on the free bodies. With the relativemotion the response of the hoist wire forces is determined. A coupling of these two parts can be made by removing the element of the hoist wire in the imposed motion model and replacing it by a pair of two nonlinear forces determined fromthe sheave wire model. These forces have an opposite sign and
are equal in absolutemagnitude and phase.

The effect of friction on dynamic hook load fluctuations is also consideredwith inputs of different amplitudes and frequencies. The hook load fluctuations at the measuring sheave are lower than applied fluctuations in the model when friction is taken into account. The simulated force at the measuring sheave is better represented with higher load fluctuations as the stick condition is exceeded earlier.