Wind-tunnel experiments on the aerodynamic interaction between two rigid sails used for wind-assisted propulsion

Wind-assisted propulsion has recently attracted attention as one viable option to drastically reduce pollutant emissions produced by ships. Despite its potential, there is still a substantial lack of understanding of the physical aspects proper of wind-assisted ships, leading to unreliable fuel-saving claims. In the context of the development of a performance prediction program for such type of hybrid ships, the research presented herewith deals with the aerodynamic interaction between two rigid sails. Wind-tunnel experiments were carried out on a single sail and on a two-sail arrangement, during which force and pressure measurements were taken on each sail. For the two-sail arrangement, two gap distances between the sails were investigated and the tests were performed at apparent wind angles ranging all typical sailing conditions. The results show that for an extended interval of moderate apparent wind angles the aerodynamic interaction has a positive effect on both sails. On the contrary, at smaller and at larger angles the interaction effects are detrimental for the downstream sail. The outcome of the present work indicates that the number of sails employed and their gap distance are important parameters to determine the aerodynamic interaction effects