The Cal 39 (Hunt/O'Day) is an American sailboat that was designed by C. Raymond Hunt and Associates as a racer-cruiser and first built in 1988. The design was originally marketed by the manufacturer as the Cal 39, but is now usually referred to as the Cal 39 (Hunt/O'Day) to differentiate it from the earlier unrelated C. William Lapworth-designs: the 1970 Cal 39, the 1978 Cal 39 Mark II and 1983 Cal 39 Mark III, which were all marketed under the same Cal 39 name.