Stanley Gibbons gives that she is a kogge (cog), but all the images of kogge types vessels carried only one mast, that I believe she is a HULC or as given on http://www.shipsonstamps.org/Topics/html/kogge.htm a HULK also given as a HOLK.
Around 1400 AD the cog had developed and changed so much that it was a new ships type called HULC, and this type developed during the 15th century and could have up to three masts as seen on the stamp.
Used as merchantmen and man-of-war in Northern Europe, the oldest type had a rocker bottom rising to narrow ends.
By the 14 century, had a keel with a stern and sternpost.
She became later flat and wide. Probably clinker planked initially, carvel by the 15th century.
Hinged stern rudder as early as the 12th century. Loose super structure or castles forward and aft by the 13th century.
By the 14th century, decked. Castles incorporated into the hull construction by the 15th century and at that time built with several decks and a flat stern.
Rigged with up to 4 masts, the fore and main mast setting square sails, the after two masts setting lateen sails.
Reported length 15 – 33 meter, capacity 1.200 tons.
The Norwegian stamp has a symbol of a salted and dried codfish.
Norway 1960 25 ore sg502, scott ?
Source: From Aak to Zumbra, A Dictionary of the World’s Watercraft.