The subject of the invention is a hydroelastic cetreboard.

Depending on its functionality, the underwater fin of a vessel is named centreboard; it protects the boat from excessive drifting. The boat design may also include a keel fin which, additionally, with its relatively big weight, ensures righting moment to prevent boat heeling. There are solutions, allowing for variable settings of centreboard, ballast or stabilising fin profile pitch by mechanical regulation of its position with regards to the boat hull (and, thereby, to the water flow around the hull). There are also solutions, enabling changes of the centreboard profile shape by means of the steering mechanism - then the lift force direction changes in result of an appropriate transverse profile of the centreboard (e.g., with the, so-called, trimtab), leaving the pitch unchanged. Sometimes, certain solutions are applied which combine both mechanisms. Changes in pitch or transverse shape profile of the centreboard are used to control the level and direction of the lift force on the centreboard, e.g., during tack changes when sailing into wind.

In Polish Application No. P.299745, an elastic centreboard of an enclosed vessel has been described, the centreboard mounted on the trailing edge. It employs roll and pitch of the boat to increase her speed.

An elastic centreboard for wind-surfing is known from Application No. EP00117231. The flexibility of the design solutions results from direct fixing to the boat, which ensures centreboard movement.

The purpose of the invention is centreboard design to reduce boat drift and indirectly increase boat speed, while being simultaneously resistant to overloads at mounting sites to the boat hull.

The hydroelastic centreboard, acc. to the invention, includes, at least, one profile, supported on, at least, two girders, preferably cylindrical. The area of the middle part of the profile, between the girders, is characterised by lower rigidity from that in the areas between the front girder and the leading edge and between the rear girder and the trailing edge.

Preferably, the profile is made of a flexible material and preferably constitutes filling of cross-section of the centreboard panel. Preferably, the area of the profile between the girders is made of a flexible material with more flexibility than areas of the profile between the front girder and the leading edge and between the rear girder, and the trailing edge. In another preferred embodiment, within the area between the girders, the profile width has been reduced to make a narrowing. Along the narrowing of the profile structural elements have been added to support the external, elastic coating of the panel in order to shape the panel cross-section in such a way as ensure laminar water flow along the panel. The elements supporting outer flexible panel coating also limit the maximal panel deflection, closing in result of deformation of the gap between them, thus hindering further deflection.

Preferably, the profiles are based on cylindrical girders in a manner allowing them to rotate freely around the girder at the point of support. Also preferably, the centreboard panel interior is filled with easily shaped flexible material to prevent water entry, and the outer walls of the centreboard are made of flexible material. In another preferred embodiment, the interior of the centreboard panel is filled with foamed polypropylene, preferably preventing water entry, further centreboard panel was coated with a flexible epoxy-glass laminate allowing for changing the shape of the profiles.

Because of the irregular shape of the profile, deflection calculations for a given boat type are done by means of computer software, using the finite element method. The desired effect, including the shape and deflection degree, is obtained by the method of successive approximation.

The panel profile rigidity is distributed along the profile cross-section, supported by the girders, while the girder layout is such that, under the effect of the pressure difference on both sides of the panel, it will change its shape, bellying into the lower pressure side. From the centreboard ferrule, connecting the girders with the hull, two girders supporting profiles of flexible material. The inside of the centreboard has preferably been filled up with material, preventing from water entry, moreover, the centreboard has preferably been coated with elastic material, allowing for profile shape changes.

The centreboard structure is characterised by elasticity, the forces of which counteract shape changes. The lift force, increased with regards to the stiff (non- steerable) solution, counteracts drifting of a sail boat, when sailing into wind, while the lack of the necessity to control the shape or position of the centreboard with regards to the hull to increase its performance, simplifies sailing. The centreboars also suppresses the dangerous boat heeling, thus increasing the safety and comfort of sailing.

The subject of the invention is presented in the following examples which do not limit in any way this invention in the drawing in which fig. 1 presents a hydroelastic centreboard in oblique, lateral view with the front wall of the centreboard, not shown on the drawing, fig. 2 presents the centreboard profile at rest with equal pressures on either side of the panel in cross-section, while fig. 3 presents the centreboard profile in deflection under pressure difference in cross- section.

Embodiment

The hydroelastic centreboard includes between coatings 11 of panel 1 inseparably fixed on ferrule 2 four profiles 4, rested on two girders 3. The area of the middle part of the profile 4, between cylindrical girders 3, is characterised by rigidity lower from that on the areas between the front girder 3 and the leading edge 6 and between the rear girder 3 and the trailing edge 5. Profile 4 is made of elastic material and constitutes filling of the cross-section of panel 1 of the centreboard. Within the area between the girders 3, the profile 4 width has been reduced to make a narrowing 8, and along the narrowing of the profile 4 structural elements 9 have been added to support the external, elastic coating 11 of the panel 1 in order to shape the panel 1 cross-section in such a way as ensure laminar water flow along the panel 1. Structural elements 9 also limit the maximal deflection value of panel 1, under the influence of deformation, and gaps 10 between them close, hindering further deflection. The profiles 4 are rested on cylindrical girders 3 in such a way as to ensure their free rotation around the girders 3 at the support point. The interior of panel 1 of centreboard if filled with easily shaped elastic material preventing the water entry.

Elastic coating 11 is made of elastic epoxy-glass laminate.

Because of the irregular shape of the profile, deflection calculations for a given boat type are done by means of computer software, using the finite element method. The desired effect, including the shape and deflection degree, is obtained by the method of successive approximation.

Unlike the known engineering solutions, the presented solution does not require any external steering mechanism for its functionality. Under the effect of water pressure, impacting the centreboard and creating over- and underpressure on it (in resuly of water flow) - the transverse profile deflects in such a way as to increase the induced lifting force. The deflection extent of the centreboard cross- section increases with rising lifting force, the level of which results from the pressure difference on either side of the panel, while, simultaneously, this deformation is counteracted by the internal forces of the structure elasticity which, when the pressures on both sides of the panel are equalised, bring back its shape to the resiting position (or significantly reduce its deflection).