To reduce the environmental impact of the maritime sector, the International Maritime Organization (IMO) has established emission limits and ambitious sustainability targets. While superyachts are currently exempt from many of these regulations, they must align with IMO’s objectives to establish the yachting industry as a responsible sector and adapt to the increasing application of these emission limits. Focusing only on new builds is not sufficient to meet ambitious targets, and sustainable refit of existing yachts is also essential. This applies not only to motor yachts but also to sailing yachts, which face unique challenges due to limited space which further complicates integrating alternative fuels like methanol or hydrogen, given their lower energy density. Despite various studies exploring alternative energy solutions, there remains a research gap in understanding the trade-offs associated with different energy configurations installable in a refit to minimize energy demand and emissions. To address this, an assessment model that evaluate technical feasibility, emissions, docking time, and Total Cost of Ownership (TCO) for different energy configurations is developed. Results from the assessment model, applied to two Royal Huisman sailing yachts of different size across various owner profiles, reveal that integrating alternative energy solutions requires significant reductions in energy demand. Feasible configurations range from using a single fuel HVO configuration for conservative owners to hybrid solutions involving HVO and methanol for more open to changes owners. Ultimately, owners willing to implement various energy reduction methods can achieve several feasible and sustainable configurations.

This thesis presents a data-driven design approach for emission reduction using bunker delivery notes (BDNs) to help support the revised IMO strategy to achieve net-zero greenhouse gas emissions by international shipping close to 2050. This research supports the Horizon Europe’s Digital Twin for Green Shipping (DT4GS) project which focuses on the development of digital twins (DTs). Part of this project involves the development of a DT-supported method for the design and retrofit of ships. DTs are a promising approach for supporting maritime decarbonization efforts due to their simulation and big data handling capability. Despite the abundance of shipping data and growing digitalization, the potential of using ship operational data for decarbonization efforts remains not fully exploited. A data-driven method such as a DT could fill this gap. However, as DTs, by definition, require real-time connection between a physical entity and the digital representation, developing a true DT for new-build alternatively fueled ship designs remains a challenge. This research thus starts by looking into retrofitting using data from existing ships.

A design framework is proposed to construct digital models to support a DT for retrofitting purpose. The proposed framework is tested on a case-study using a 300-meter bulk carrier. Since January 2019, operational ship data is collected through BDNs, a mandatory data collection method for ships of 5000 GT and above, adopted by the IMO. Constructing a DT based on BDNs is considered to be convenient as it provides a solid source of operational data in the future.

First, the available data from the BDNs is preprocessed using an adopted framework based on data science literature. The resulting 5,678 data points are used for the construction of a model representing the bulk carrier and a model representing the green ship technologies part. A fuel consumption model is constructed to represent the bulk carrier. It utilizes a gray-box modeling approach, consisting of a white-box resistance model and a black-box artificial neural network. Both models incorporate environmental-dependent inputs. The investigated green ship technologies for the potential retrofit are represented by various wind-assisted ship propulsion (WASP) systems, namely a towing kite, a DynaRig sail, and a Flettner rotor. These systems are modeled using a white-box modeling approach, together with available wind data. Using an adopted integration framework, based on the propeller-engine matching procedure, both representations are combined into one green ship digital model.

An environmental assessment is performed using the IMO's EEXI and CII assessment tools, respectively evaluating the design and operational aspects of the potential retrofit. Additionally, a financial assessment is conducted using the payback period. Results showed the design implications and emissions reduction potential of implementing such systems which will guide the retrofit decision by the ship's owner.

Facing the critical challenge of reducing greenhouse gas (GHG) emissions in the maritime industry, this thesis explores the potential of smart control systems using Reinforcement Learning (RL) for autonomous sailing. Traditional controls for sailing fall short in navigating the complex, dynamic conditions of maritime environments. RL has shown to be effective for continuous control applications in these types of conditions, however, primarily in simulated environments. Therefore, this study aims to show the potential of RL for autonomous sailing control (ASC) by means of a small scale project. A fast-time simulation of an Optimist is used to train the sailing controls required to reach an upwind target. The controls are then transferred to a robotized Optimist in a real-world environment to test the transferability of the simulation trained controls. First, the reality gap, or modelling error, between the simulation and real-world environment is quantified to be able to assess the performance of the used techniques to bridge the existing gap. The sim-to-real techniques of Domain Randomization (DR) and the addition of observation noise (ON) are applied during the training process. To test the effectiveness of the trained RL controls, the best performing ones in the simulation are selected and tested in the real-world environment. The performance of the RL controlled Optimist is compared to state-of-the-art controls in robotic sailing. Their performances are measured and compared by means of success rate and a physics-based metric that calculates the efficiency of the sailboat to use the power of the wind to propel itself, called the energy ratio. The results show that the RL controls are highly successful in the sailing simulation, however, the transfer to the real-world remains a major challenge. DR does improve the sim-to-real transfer, resulting in an agent that is able to reach a 100% success rate throughout 12 runs in the real-world environment.

Due to the IMO regulations on emissions, Wind Assisted Propulsion Systems have become more and more interesting for shipowners. One of those Wind Assisted Propulsion Systems is the VentoFoil from Econowind. However, to enable the decision of the shipowner on whether and where to place VentoFoils on board, this research aimed to construct a VentoFoil Adoption model, assessing the environmental and financial consequences of specific VentoFoil placement options. With this, the main research question is: ‘What is the impact of VentoFoil placement on ships from a ship owner’s perspective?’ The VentoFoil Adoption Model for Econowind required a Technology Adoption Decision-support model that could operate within a short computational time while incorporating an adaptable weather matrix. During the literature study on the existing models regarding WASP models, a research gap was identified. The gap primarily lies in integrating low-fidelity force modelling with financial decision support.

The VentoFoil Adoption model was constructed with a baseline calculation in which no VentoFoils were placed onboard. This baseline included the hull resistance and the wind forces on the deckhouse for all possible wind directions and speeds. After that, the VentoFoils were placed on deck, for which the VentoFoil forces were added with respect to the baseline calculations. The VentoFoil forces were calculated including the interaction between the deck and the VentoFoils, using a turbulent separation layer. The interaction between the deckhouse and the VentoFoils was simulated using a triangle shape in which the wake is turbulent. Lastly, the interaction between the VentoFoils was included using a parametrized wakefield in which the apparent wind angle changed based on the distance between the VentoFoils. From the resulting polar plots, the financial and environmental benefits of VentoFoils are illustrated. Fuel savings are achieved when sailing at reference speed and lower power, and increased cargo yield is realized at higher speeds with reference power. This is dependent on the weather probability matrix.

To demonstrate the practical application and effectiveness of the model, a case study was performed using the VentoFoil Adoption Model on the Magritte, a bulk carrier currently sailing with two 16-meter VentoFoils. From a shipowner’s perspective, the conclusion was made that two 30-meter VentoFoils would in the long term be more cost-effective. For most combinations of fuel price and cargo yield, the payback time of the case at reference power and thus higher sailing speed was lower, making it the favourable operational decision.

A validation using the ‘validation square method’ was performed on the method used within the VentoFoil Adoption Model. The empirical performance validity was investigated by comparing the results from the sea trial data of the MV Sunnanvik and the results from the model. The results are within a reasonable range.

The answer to the main research question can be found with the model. Multiple placement options can be inserted, giving the benefits and costs for well-considered decision-making of the ship owner on whether and where to place VentoFoils on board.

There is uncertainty as to whether the stability criteria in the Dutch regulatory framework for commercial cruising vessels are safe and obtainable for the current Dutch commercial sailing fleet. Therefore, this paper aims to determine a suitable set of intact stability requirements for monohull sailing vessels operating under the Dutch flag, striking a balance between safety and practicality. A literature review was conducted to identify potential stability risks and the state-of-the-art of sailing stability criteria. Models of representative vessels in the Dutch sailing fleet have been defined to study the practicality and safety level of various stability criteria in more detail. It is concluded that the current criteria are not obtainable for sailing yachts designed to sail at large heel angles. Moreover, it was found that the current criteria cannot identify vessels that can be vulnerable to squalls or waves. Therefore, a new set of criteria is proposed, which is more practical for vessels in the Dutch commercial sailing fleet, whilst providing an improved measure of safety.