A wingsail structure for a wind-assisted propulsion arrangement of a marine vessel, the wingsail structure comprising: - a wingsail frame comprising: ∘ a rigid or semi-rigid main wingsail having an aerofoil shape with a leading edge, a trailing edge, a top end and a bottom end, and side walls (211; 212) extending therebetween, ∘ a rigid or semi-rigid flap having an aerofoil shape with a leading edge, a trailing edge, a top end and a bottom end, and side walls (221; 222) extending therebetween, ∘ at least one upper coupling member and at least one lower coupling member connecting the main wingsail and the flap, - a foundation arranged to be fixed to a body of the vessel, the foundation being associated with the wingsail frame such that the wingsail frame is rotatable in respect to the foundation via a first vertical axis of rotation, wherein the upper and lower coupling members (130; 140) are configured to: - bring the main wingsail and the flap to a first unfolded standing position, and - bring the main wingsail and the flap towards one another to a second folded standing position (IIa; IIb) to reduce generated forces and the space required by the wingsail frame on board of the vessel, and where the main wingsail and the flap are in an overlapping position when looking in a transversal plane when in the second folded standing position, and wherein the wingsail structure further comprises a tilting arrangement configured to bring the wingsail frame from the second folded standing position (IIa; IIb) to a third tilted position (IIIa; IIIb) in respect to the foundation. - a wingsail frame comprising: ∘ a rigid or semi-rigid main wingsail having an aerofoil shape with a leading edge, a trailing edge, a top end and a bottom end, and side walls (211; 212) extending therebetween, ∘ a rigid or semi-rigid flap having an aerofoil shape with a leading edge, a trailing edge, a top end and a bottom end, and side walls (221; 222) extending therebetween, ∘ at least one upper coupling member and at least one lower coupling member connecting the main wingsail and the flap, ∘ a rigid or semi-rigid main wingsail having an aerofoil shape with a leading edge, a trailing edge, a top end and a bottom end, and side walls (211; 212) extending therebetween, ∘ a rigid or semi-rigid flap having an aerofoil shape with a leading edge, a trailing edge, a top end and a bottom end, and side walls (221; 222) extending therebetween, ∘ at least one upper coupling member and at least one lower coupling member connecting the main wingsail and the flap, - a foundation arranged to be fixed to a body of the vessel, the foundation being associated with the wingsail frame such that the wingsail frame is rotatable in respect to the foundation via a first vertical axis of rotation, wherein the upper and lower coupling members (130; 140) are configured to: - bring the main wingsail and the flap to a first unfolded standing position, and - bring the main wingsail and the flap towards one another to a second folded standing position (IIa; IIb) to reduce generated forces and the space required by the wingsail frame on board of the vessel, and where the main wingsail and the flap are in an overlapping position when looking in a transversal plane when in the second folded standing position, and - bring the main wingsail and the flap to a first unfolded standing position, and - bring the main wingsail and the flap towards one another to a second folded standing position (IIa; IIb) to reduce generated forces and the space required by the wingsail frame on board of the vessel, and where the main wingsail and the flap are in an overlapping position when looking in a transversal plane when in the second folded standing position, and wherein the wingsail structure further comprises a tilting arrangement configured to bring the wingsail frame from the second folded standing position (IIa; IIb) to a third tilted position (IIIa; IIIb) in respect to the foundation.