Surfboard speed indicator - has eddy current meter and impeller-driven rotating magnet and electrically conducting detector bell

摘要

The device is contained in a cylindrical housing (1, 2) and is inserted in the surfboard (15, 16). It is covered by a transparent screen (5) through which the indicator needle is viewed. An impeller (13) connected to a shaft (12) protrudes from the bottom of the surfboard. A magnet (10) is fixed to the other shaft end and is covered by a non-magnetic, water tight isolating wall (4). The revolving magnet causes eddy currents in the electrically conducting bell (9) attached by an axle (8) to the indicator needle and held by a restoring spring (11). This assembly forms an eddy current meter whereby the needle rotation is proportional to the surfboard speed. The speed is read off the scale (6).