The increasing size and mass of offshore wind monopiles (MPs) present significant challenges for the conventional installation methods, primarily due to limited crane capacities. Vessels with sufficient crane capacity to install future generation XXL MPs, exceeding 3000 t, are scarce and expensive. This creates a need for alternative installation methods that allow the use of existing equipment.

Buoyancy-Assisted Installation (BAI) offers a promising solution to this challenge. Buoyancy has the potential to generate additional lift during the upending and lowering phases of monopile installation, thereby reducing the effective load on the crane. That could enable existing vessels to install larger monopiles without exceeding their crane limits, or requiring costly vessel upgrades.

While current BAI methods mainly explore the use of end caps to seal the MP and generate buoyancy, these caps introduce operational risks. Failure of caps can lead to the monopile sinking, costly delays, and safety hazards such as equipment damage or risk to nearby personnel. Therefore, this thesis specifically investigates the feasibility of using inflatable buoyancy bags for BAI. The use of buoyancy bags is attractive due to their light weight, their adjustable buoyancy through inflation or deflation, and their safety provided by redundancy when using multiple bags.

The research follows an engineering design process. It includes a hydrostatic MP stability study and the development of four buoyancy bag concepts. These concepts were evaluated through a Multi-Criteria Decision Analysis (MCDA), leading to the selection of the most promising configuration. This concept was further investigated through numerical simulations using OrcaFlex and OrcaWave, assessing hydrodynamic performance across various wave conditions and MP upend angles.

Results show that the proposed buoyancy bag configuration can reduce crane loads significantly. The study concludes that buoyancy-assisted upending with external bags could provide a feasible solution for installing monopiles whose weight exceeds the available crane capacity.