Abstract: A buoy is provided with first and second fixed hydrodynamic surfaces (15,16). When the buoy is towed through water by a tether (17), the first hydrodynamic surface (15) generates a downward force that reduces with increased speed through the water. The second hydrodynamic surface (16) generates an upward force that increases with increased speed through the water so that the buoy dives up to an upper critical speed through the water speed and rises beyond said upper critical speed through the water. The downward force of the first hydrodynamic surface (15) overcomes the buoyancy of the buoy at a lower critical speed through the water above, which the buoy dives. The hydrodynamic surface (15) comprises first fins (15) mounted on an outer casing (1) of the buoy and are spaced angularity and extend parallel to the center axis of the buoy which is substantially aligned with the direction of towing.

Abstract: A buoy is provided with first and second fixed hydrodynamic surfaces (15,16). When the buoy is towed through water by a tether (17), the first hydrodynamic surface (15) generates a downward force that reduces with increased speed through the water. The second hydrodynamic surface (16) generates an upward force that increases with increased speed through the water so that the buoy dives up to an upper critical speed through the water speed and rises beyond said upper critical speed through the water. The downward force of the first hydrodynamic surface (15) overcomes the buoyancy of the buoy at a lower critical speed through the water above, which the buoy dives. The hydrodynamic surface (15) comprises first fins (15) mounted on an outer casing (1) of the buoy and are spaced angularity and extend parallel to the centre axis of the buoy which is substantially aligned with the direction of towing.