## 5 Concluding Remarks  
A method to reconstruct the movements of a sailboat in order to get a reliable estimate of wave parameters, using GPS receivers, is presented. It is based on the combined approach of the Kin-VADASE and Moving Base Kinematic techniques. The proposed method was applied to the records collected onboard the ECO40 sailboat during a storm in the Western Mediterranean Sea. Three GPS antennas were deployed on the sailboat. Their positions were measured by means of a survey performed when they were installed. Therefore, the three-dimensional locations of the GPS antennas suffice to infer the three-dimensional position and attitude of the boat as a rigid body, hence to reconstruct wave parameters. A fourth GPS antenna could be considered to improve the reliability of the estimation of the position and attitude of the boat.  
Wave properties as derived on the basis of the estimated boat movements were compared to available wave data. It appears that the wave properties were calculated with a high degree of accuracy. Note that the main aim of this work was the estimation of wave parameters, hence the GNSS data analysis was not directly validated. Of course, the good agreement between estimated and available data may be viewed as an indirect validation of GNSS data analysis as well.  
In general, the techniques proposed in this paper appear to be suitable to estimate the 6 DOFs movements of sailboats navigating offshore, where onshore reference receivers or GNSS network cannot be used to correct GPS errors. The motion of the boat can provide quantitative information for many important practical applications, such as the improvement of autopilots, the analysis and the optimization of ship performances, and the estimation of local wave properties. Furthermore, it can be used to correct wind measurements carried out onboard sailboats.  
Conceptualization, P.D.G., M.C. ([PERSON]) and A.R.; Methodology, P.D.G., M.C. ([PERSON]), A.R., A.M., M.D.R., D.P., G.B., M.C. ([PERSON]) and P.S.; Software, A.R., A.M. and D.P.; Validation, P.D.G., M.C. ([PERSON]); Formal Analysis, P.D.G., M.C. ([PERSON]), A.R., A.M., M.D.R., D.P., G.B., M.C. ([PERSON]) and P.S.; Investigation, P.D.G., M.C. ([PERSON]), A.R., A.M., M.D.R., D.P., G.B., M.C. ([PERSON]) and P.S.; Resources, P.D.G. and M.C. ([PERSON]); Data Curation, A.R. and A.M.; Writing--Original Draft Preparation, P.D.G., M.C. ([PERSON]), A.R., A.M., M.D.R., D.P., G.B., M.C. ([PERSON]) and P.S.; Writing--Review & Editing, P.D.G., M.C. ([PERSON]), A.R., A.M., M.D.R., D.P., G.B., M.C. ([PERSON]) and P.S.; Visualization, A.R. and D.P.; Supervision, P.D.G and M.C. ([PERSON]).  
This research received no external funding.  
Figure 7: (**Top**) Comparison between the significant wave height measured onboard and the available wave data; and (**Bottom**) comparison between the mean spectral wave direction as estimated by means of the proposed method and the same quantity as obtained by the ECMWF data (red line) and Alghero wave buoy data (blue dots). The red dashed lines refer to four points of interest along the route (as shown in Figure 2).  
**Acknowledgments:** [PERSON] (IDRO-GEOTEC) is acknowledged for his help and expertise during the installation of the instruments. The skipper [PERSON] is also acknowledged for his contribution. A special acknowledgement is due to Leica Geosystem for providing the high-precision GPS receivers and to [PERSON] for providing the DICCA wave data.  
**Conflicts of Interest:** The authors declare no conflict of interest.