Abstract
In order to estimate the construction cost of floating offshore wind turbines (FOWTs) more precisely than before, it is necessary to calculate the installation time of FOWTs more precisely. Therefore, we proposed a model to estimate the installation time of FOWTs by dividing the offshore construction into major processes and quantitatively evaluating the efficiency of each installation process. On the basis of the Cost Breakdown Structure (CBS), the total offshore installation time can be formulated as the sum of the installation time of the following five processes: (1) pre-anchoring, (2) verification of anchor ultimate holding capacity, (3) towing, (4) mooring, and (5) other operational processes. This study introduces “installation time per mooring line” as a benchmark for measuring efficiency. First, the model proposed in this paper is applied to an FOWT demonstration project in Japan and the efficiency of the installation processes is analyzed. It is found that the installation time per mooring line for (2) verification of anchor ultimate holding capacity and (4) mooring were reduced by 69% and 95%, respectively, from the initial time. The proposed model is also applied to a large wind farm and the authors conduct a sensitivity analysis. It is concluded that the installation time for (1) pre-anchoring is the most strongly affected by the number of mooring lines per FOWTs. The installation time for (1) pre-anchoring was 1.6 times longer than that of (2) verification of anchor ultimate holding capacity and eight times longer than that of (4) mooring. This study revealed that (1)pre-anchoring and (2) verification of anchor ultimate holding capacity are expected to have a large impact on cost reduction and improve efficiency.