The 9.30-metre sailing yacht Neptunus was one of the first generation fibreglass sailing yachts built around the 1960s for an American client. Three types were produced: the 12.50-metre Bonito series, the William Tripp designed 9.30 and 11.30-metre sailing boats, and a series of a larger type, Javelin, of the same designer William Tripp, ranging between 10 and 15 metres. The fibreglass hull and superstructure were produced at Werkspoor in Utrecht. The carpentry and the installation of the engine were done at the Kaag.