Provided are a floating structure fluid dynamic force use system and a wind-propelled vessel which uses the system whereby it is possible to compensate for overturning moment due to fluid dynamic force and to alleviate both tilting and size increases of a floating structure. A floating structure fluid dynamic force use system (1) comprises an assembly (12) which extracts energy from wind or water, and a floating structure (13) which supports the assembly (12). The assembly (12) comprises a wind receiving part (10) which receives fluid dynamic force, and a support column (11) which supports the wind receiving part (10). The assembly (12) is positioned with the center of gravity (15) thereof below the water line and is supported to be capable of tilting in an arbitrary direction upon the floating structure (13).

A method is described for steering of an un-manned ocean vessel (10), where the vessel comprises a hull (12), a self-tacking wing sail (16) for propulsion, a keel (18) for direction stability and a rudder (20). The method comprises the steps: to set the rudder (20) and the sail (16) so that the vessel (10) holds a stable direction with regard to the wind at a given rudder deflection, a) to check the position of the vessel (10) with the help of an electronic steering system (22) on board, and if it is registered that the vessel (10) is not getting any nearer its destination, b) adjust the rudder (20) to set a new, arbitrary course, where the course is chosen from among a number of pre-determined course changes, c) check again the position of the vessel (10) with the help of the electronic steering system (22) and if it is registered that the vessel (10) has got nearer its destination, d) to let the vessel (10) continue on the same course, and e) to repeat said check of the position of the vessel (10) and the steps a) to d) at regular intervals.

A hollow kite control bar is provided with means for sliding access to the bar for one or multiple lines or groups of lines. Each line has one end towards the kite and the other towards the bar. The length of each line between the kite and the bar can be adjusted by pulling into and releasing from the bar, which length or lengths can be locked at multiple positions in one or more locking means fixed to the bar. The excess line length pulled in is automatically held inside the bar.

A hollow kite control bar is provided with means for sliding access to the bar for one or multiple lines or groups of lines. Each line has one end towards the kite and the other towards the bar. The length of each line between the kite and the bar can be adjusted by pulling into and releasing from the bar, which length or lengths can be locked at multiple positions in one or more locking means fixed to the bar. The excess line length pulled in is automatically held inside the bar.