The sea surface is a harsh environment, with many mechanical stresses, corrosion and wear. An unmanned surface vehicle has to withstand this environment for long periods of time. The Sailbuoy is designed and tested to withstand the environmental stresses of the North sea, cold, severe weather and little sunlight during the winter. Our extensive testing in these conditions has shown us that robustness is vital for a surface vessel to withstand months at sea. The Sailbuoy navigates satisfactorily in harsh environmental conditions and high sea state with impeccable performance. It tolerates obstacles and ice to some degree.