## 1 Introduction  
The development of drones has allowed the non-invasive monitoring and exploration of remote areas on Earth. To monitor the oceans using unmanned vehicles, autonomous underwater vessels (AUVs) can be deployed below the sea surface, and while their ability to navigate at different depths allows them to be covert, their construction is expensive to sustain the water pressure. As an alternative, unmanned surface vehicles (USVs) such as the wave glider can monitor the ocean at the air-water interface [1, 2]. In the past few years, autonomous sailboats have gained interest as a USV, since they provide a low-cost, sustainable solution to monitor the oceans using a silent propulsion system. In fact, the sailboat is particularly attractive to monitor marine mammals [3, 4] because it is nonthreatening to animals. There have been a number of initiatives to design and optimize the sailboat for various missions. Saildrone commercialized a 7 m long vessel with a rigid sail. Its average speed is on the order of 2 knots [4, 5]. Moreover, a number of competitions were initiated in the past 10 to 15 years. Originally, missions were short, and early competitions were held on lakes. In 2005, the Microtransat Challenge was launched with the ambitious goal to cross the Atlantic Ocean using robotic sailboats with a maximum length of 2.4 m to prevent damage to other vessels. Two classes exist: fully autonomous designs, in which communication to the sailboat is not allowed, and the unmanned division that allows data to be sent to the boat. Since then, 27 autonomous sailboats have attempted the challenge; however, none have successfully completed it. A single boat, the SB Met, completed it in the unmanned division. In 2015, the Faculty of Engineering at Dalhousie University participated in the Microtransat for the first time, in collaboration with Ensta-Bretagne to create the Breizh Tigresse. The hull chosen was that of the Breizh Spirit, a vessel that was developed by Ensta-Bretagne. New sails and rigging were mounted on the hull. New controller electronics were fabricated to replace the system that was damaged in the Breizh Spirit's previous mission. In comparison to the Breizh Spirit, the major difference was that the Breizh Tigresse was powered with a non-rechargeable battery pack. The Breizh Tigresse was launched 5 NM off the coast of St. Margaret's Bay in Nova Scotia. She sailed under control for approximately 10 days, and at this time a significant change in her behaviour led us to believe it had sustained damage, potentially from a cargo ship that crossed its path. After the 2015 attempt with the Breizh Tigresse, the team at Dalhousie designed a new sailboat that was targeted to withstand ocean conditions and collisions for over three months. The objective of this paper is to describe the design procedure for the SeaLeon. A few autonomous sailboat designs have been documented in the literature. In [6], the authors described a sailboat design intended for short missions; therefore, the design did not have to withstand harsh conditions for long periods of time. In [7], the authors described the design, development, construction and demonstration of a small, robotic research vessel propelled by both wind and motor. The two-meter vessel was capable of speeds of up to five knots under sail and six knots using an electric motor without the need for human interaction. A controller was described to manage the navigation, and the length of the boat was 1.38 m. More recently, a sailboat controller design for the Microtransat was documented in [8]. Furthermore, in 2010, to develop a robust sailboat deployed for long-term missions, a model of the robot was developed in [9] and utilized real environmental conditions to optimize the sailboat characteristics. While the design was described, an analysis of the performance during its mission was not included to optimize the different characteristics of the sailboat. A robust mechanical design is necessary to withstand rough water conditions or harsh weather.