shipstamps.co.uk

The mythological treasure ship (Takarabune 宝船) is laden with treasure (Takara 宝). Says JAANUS: “The Chinese character BAKU 獏, a Chinese imaginary animal thought to devour (i.e. prevent) nightmares, is sometimes found written on the sail. Often auspicious cranes and tortoises are depicted in the sky and the sea. Although the origin of treasure-boat paintings is not clear, one Edo-period record indicates that they were started in the Muromachi period.

http://www.onmarkproductions.com/html/seven.shtml
Japan 1971 7/10y sg1277/78 1999 50y sg ?, scott?