A watercraft structure comprising: - a hull; - a lifting surface connected to said hull and immersed at least partially in water, said lifting surface adapted to generate a lift force suitable for supporting said hull, said lifting surface comprising a movable portion arranged to rotate relatively to said watercraft, between a position of higher lift and a position of lower lift; - an actuating mechanism arranged to actuate said movable portion between said positions of higher and lower lift, said actuating mechanism comprising: - a containing volume comprising a first chamber at a pressure P a and a second chamber at a pressure P b divided by a septum, said septum having a first face having surface S a and oriented towards said first chamber and a second face having surface S b and oriented towards said second chamber; - a reference channel hydraulically connected to said second chamber, said reference channel being in communication with the external environment by a reference opening that, in use, is constantly below the level of the water and is oriented in motion direction; - a compensation channel hydraulically connected to said first chamber, said compensation channel being in communication with the external environment by at least one respective compensation opening located at a greater higher with respect to said reference opening, said or each compensation opening being oriented in motion direction; said actuating mechanism being configured in such a way that: - when P a ∗ S a > P b ∗ S b there is a relative movement between said septum and said chambers (141,142) arranged to reduce the volume of said second chamber and for making the rotation of said movable portion towards said position of higher lift; - when P a ∗ S a < P b ∗ S b there is a relative movement between said septum and said chambers (141,142) arranged to reduce the volume of said first chamber and to produce the rotation of said movable portion towards said position of lower lift; - when P a ∗ S a = P b ∗ S b there is no relative movement between said septum and said chambers (141,142), and said movable portion does not rotate; said watercraft structure characterized in that said actuating mechanism comprises an auxiliary reference channel hydraulically connected to said second chamber and communicating with the external environment by an auxiliary reference opening that, in use, is constantly above the level of the water, in such a way that the pressure P b in said second chamber is equal to ( P w + P atm)/2, where P w and P atm are, respectively, the water pressure and the atmospheric pressure at the height of said actuating mechanism. - a hull; - a lifting surface connected to said hull and immersed at least partially in water, said lifting surface adapted to generate a lift force suitable for supporting said hull, said lifting surface comprising a movable portion arranged to rotate relatively to said watercraft, between a position of higher lift and a position of lower lift; - an actuating mechanism arranged to actuate said movable portion between said positions of higher and lower lift, said actuating mechanism comprising: - a containing volume comprising a first chamber at a pressure P a and a second chamber at a pressure P b divided by a septum, said septum having a first face having surface S a and oriented towards said first chamber and a second face having surface S b and oriented towards said second chamber; - a reference channel hydraulically connected to said second chamber, said reference channel being in communication with the external environment by a reference opening that, in use, is constantly below the level of the water and is oriented in motion direction; - a compensation channel hydraulically connected to said first chamber, said compensation channel being in communication with the external environment by at least one respective compensation opening located at a greater higher with respect to said reference opening, said or each compensation opening being oriented in motion direction; - a containing volume comprising a first chamber at a pressure P a and a second chamber at a pressure P b divided by a septum, said septum having a first face having surface S a and oriented towards said first chamber and a second face having surface S b and oriented towards said second chamber; - a reference channel hydraulically connected to said second chamber, said reference channel being in communication with the external environment by a reference opening that, in use, is constantly below the level of the water and is oriented in motion direction; - a compensation channel hydraulically connected to said first chamber, said compensation channel being in communication with the external environment by at least one respective compensation opening located at a greater higher with respect to said reference opening, said or each compensation opening being oriented in motion direction; - when P a ∗ S a > P b ∗ S b there is a relative movement between said septum and said chambers (141,142) arranged to reduce the volume of said second chamber and for making the rotation of said movable portion towards said position of higher lift; - when P a ∗ S a < P b ∗ S b there is a relative movement between said septum and said chambers (141,142) arranged to reduce the volume of said first chamber and to produce the rotation of said movable portion towards said position of lower lift; - when P a ∗ S a = P b ∗ S b there is no relative movement between said septum and said chambers (141,142), and said movable portion does not rotate;