Electromagnetic boat speedometer having removable electrodes

An electromagnetic speedometer suitable for use in a boat including a hull having an upper interior surface and a lower exterior surface in contact with a body of water, the hull containing a plurality of spaced through openings, comprising:

• (a) a plurality of electrode assemblies arranged adjacent to respective through openings in the boat hull, each of said electrode assemblies including
• (1) a penetrator valve mounted on the hull upper surface and surrounding a respective through opening;
• and
• (2) an electrode supported by each penetrator valve for insertion and removal from the respective through openings in the boat hull, said electrodes each having a tip at one end to engage the water when said electrodes are inserted into the respective through openings, said penetrator valves permitting removal of said electrodes and cleaning of the electrode tips when the boat is in the water while preventing water from entering the boat;
• (b) an annular coil adapted for mounting on the boat hull upper interior surface and having an inner diameter extending beyond the through openings in the boat hull, said penetrator valves and said electrodes being arranged in spaced relation within said inner diameter of and separate from said annular coil, said annular coil being configured to establish an electromagnetic field in the water large enough to allow a speed measurement to be made by said electrodes substantially away from boundary layer influences resulting from movement of the boat hull;
• and
• (c) a velocity measuring circuit including a plurality of conductors, respectively connected with other ends of said electrodes, said velocity measuring circuit generating a velocity signal in response to speed measurements from said electrodes.