Apparatus for sensing movement of an object relative to a fluid

Disclosed is inter alia an apparatus (63) for sensing a movement of an object (10, 11) relative to a fluid (12, 13), e.g. for sensing relative movements of a surf board in water. A particular characteristic of the invention is that the housing (21) is mounted in fixed arrangement to a surface (20) of the object, the housing receiving a spring member (62) having a plurality of blades (25a, 25b, 25c, 25d), wherein each blade has an outer end (27) which is fixed to the housing, and an inner end (28) which is connecting to a center portion (65) of the spring, the plurality of blades defining a plane (73), wherein a plurality of strain gauges (26a, 26b, 26c, 26d) is positioned on the blades, and wherein a rigid pin (17) is mounted on the center portion of the spring member which is extending in a direction of a normal vector (74) of the plane and which is protruding from the surface (20) of the object and configured to dip into the fluid.