## 5 Testing and Navigation
### Achievements  
A comparison of the SeaLeon and Breizh Tigresse performance is of great interest, since the mechanical design of the two vessels had important differences. In the span of one week, the Breizh Tigresse travelled 230.0 NM in terms of VMG while Sealeon sailed 922 NM in 28 days for a weekly average of 230.5 NM. For SeaLeon, the launch date was chosen with a particular attention to the weather forecast. The drone made its best 24 h performance on the first day, with 55.8 NM travelled for a speed average of 2.32 knots at the top speed of the velocity polar diagram (Table 6). A Froude similarity was applied and demonstrated that SeaLeon should have been expected to be 12% faster. However, the average performance for both vessels was close despite the difference in size. In practice, this is partly due to the more efficient hull of Breizh Tigresse and the fact that SeaLeon was slightly underpowered, as it inherited the same sail plan as Breizh Tigresse despite an 80% higher displacement. During the mission, the Breizh Tigresse showed a top speed of 6.6 knots, while SeaLeon achieved a top speed of 6.0 knots. This may be explained by the surfing qualities of the first hull. A good behavior in rough conditions and the ability to keep the trajectory under control may influence the choice of hull design to avoid high hydrodynamic loads. However, such performances are too rare to be conclusive. It is interesting to note that during the SeaLeon's mission, the currents had a significant impact on its route. Figure 7 shows the sea surface water velocity on 28 August 2018. The limit between the Grand Banks and the Flemish Cap can be seen with the Labrador current from the north to the south in light green while engag  
\begin{table}
\begin{tabular}{c c c c c c} \hline
**TWA\(\backslash\)TWS** & **10** & **15** & **21** & **32** & **40** \\ \hline
**0** & 0 & 0 & 0 & 0 & 0 \\
**30** & 0.64 & 0.74 & 0.83 & 0.95 & 1.03 \\
**45** & 0.83 & 0.95 & 1.07 & 1.22  
To the east of the Flemish Cap, between longitudes 42\({}^{\circ}\) W and 45\({}^{\circ}\) W, a deviation of the Gulf Stream towards the north can be observed. The current in this area can reach 1.4 m/s, twice the average VMG of SeaLeon. In fact, the Gulf Stream trajectory matches the SeaLeon trajectory towards the North well at that position in time. The same trajectory pattern was also observed at the same location by [PERSON] with OpenTransat in 2019 ([[https://track.opentransat.com](https://track.opentransat.com)]([https://track.opentransat.com](https://track.opentransat.com)), accessed on 08/29/2021). It is, therefore, quite possible that, although the SeaLeon deviated by almost 200 NM north of its route, it was still under control until 20 September 2018, 41 days after its launch. The deviation towards the north visible on Figure 4 would only be due to the vigorous influence of the Gulf Stream. In fact, between 7 and 13 September, SeaLeon resumed its course towards the next waypoint with constancy. Given the strength and unsteadiness of the Gulf Stream, it is difficult to equate the erratic nature of the trajectory of the sail drones in this area with a system failure. Nevertheless, after 3 September, the VMG over 24 h fell by between 30% and 47%, even though the Gulf Stream is supposed to be favorable on average, particularly in this area. With regard to the realized performance, the project can be considered to be very successful. Following up on previous attempts, originally with the Breizh Spirit in 2011 and 2012, then Breizh Tigresse in 2015, Sealeon improved the performance with a new record in time and distance covered by an autonomous sailboat in 2018. The SeaLeon's voyage lasted 76 days before the final remote communication at LAT 45\({}^{\circ}\)30\({}^{\prime}\)30\({}^{\prime\prime}\) N, LON 34\({}^{\circ}\)32\({}^{\prime}\)30\({}^{\prime\prime}\) W. At the time, this was a record of endurance. After its last position report on 14 October, it was found on February 21 st at Trahan Strand near Castletownpe, County Cork, Ireland.