## 1 Introduction
The design requires a strong sail capable of propelling the sailboat, as well as a solid hull that can maintain buoyancy while carrying the sailboat's system devices. In [10], a rigid free-rotating sail was considered as a method of withstanding harsh weather conditions while maintaining sailing performance. They designed the rig using a Vortex Lattice Method combined with a Velocity Prediction Program to maximize aerodynamic performance. Furthermore, in [11], the authors described the Roboat ASV based on the commercially available Laerling 3.75 m sailboat type. The model focused on safety and stability. In [12], the boat used a mono-hull with a passive keel and large foam thickness to ensure that the boat maintained buoyancy if flooded. In comparison to previous work, in this paper, the mechanical design is specifically intended to optimize the sailboat's robustness, and considers the extended mission duration for a transatlantic crossing from west to east. To account for the harsh ocean conditions, an analysis is completed to ensure that the boat is self righting. Further, as is explained, the configuration of the sail, rigging and rudder is intended to reduce energy consumption. To extend the mission time, an efficient controller is essential. The integration of the controller includes a choice of sensors and actuators as well as the programming of a low-complexity navigation on a low-power processor. In [13], the sensors and actuators were taken into consideration to optimize the vessel performance. A data logger stored timestamped information on sensor readings as well as information about the working of the system. This allowed the performance and behavior of the system to be studied post testing. Similarly, in [14], a simulation of the vessel controller was performed in Matlab. More recently, [PERSON] et al. utilized machine learning algorithms [15] to optimize their path planning. In [16], careful analysis of the tacking in different wind conditions was documented. Compared with traditional research into sailboats based on acquiring wind speed and direction by a large wind sensor and controlling the system by a velocity polar diagram, to further increase the speed and motion agility, the authors propose an alternative way based on the Force Polar Diagram (FPD). As is shown, the SeaLeon's controller attempts to realistically represent how a sailor controls the rudder and sail depending on the wind conditions using very low energy sensors and actuators, and a set of waypoints programmed into the boat's memory manages the vessel's path. In [17], the focus is on hybrid energy management, and takes into consideration instantaneous energy supply for the motors and adjusts the rudder and sails accordingly. In [6], the sailboat uses solar panels as the main power supply along with a direct methanol fuel cell as backup power. Solar panels are a popular method of supplying energy for sailboats designed for longer missions. The same design was used for the Peruugas [12] and for the ASV Roboat [6]. In this work, a non-rechargeable energy-efficient battery source is compared to alternative solutions relying on solar energy to justify our choice and extend the lifetime of the drone. The rest of this paper is organized as follows. In Section 2, the navigation system characteristics are reviewed; in Section 3, the mechanical design is described; in Section 4, the electrical system, including the real-time controller, and the energy supply are proposed; in Section 5, a test procedure and a trajectory definition taking into account the risk of collision and the weather conditions are presented; finally, in Section 6, conclusions are provided.