An outboard motor for small watercraft, such as a pleasure boat, has a capability of changing between a forward shift position and a reverse shift position by causing a lower part of the unit to rotate in small increments and move along an arc formed by a ratchet plate secured above the propeller assembly. The radar receiver comprises a receiving antenna positioned at a predefined distance from the transmitting antenna. Oil flowing down from an oil return passage provided in the cylinder block and oil flowing down from a blow-by gas passage, flow downwards from an upper end of the oil guide groove and return through an opening to an oil pan. Each lens provides an optical power that is part of a net optical power of the series of lenses when a patient views through the phoropter.