It is a collective name of a great number of the Rhine vessels beginning from the 16th century. The oldest picture of an aak is represented in the work 'Wonsam Prospekt' from Cologne (1530). It was a 'Keulche (Cologne) Aaken' - a small clinker-built cargo ship with a half-rounded hatching deck, flat-bottomed and without fore- and sternposts. The ship's bottom with the help of bow and stern pieces at both ends flatly and obliquely raised beginning from the waist. This aak had no side sheet anchors and carried a simple sprint sail and a forestaysail. Variations of such type of a ship were Samoreusen, Bonder, Dorstensche, Aaken, Neckaraaken. All of them were clinker-built and only in the 18th century on some of them a sternpost appeared. A slope flat bottom formed the bow of the ship. The short bowsprit gave possibility to carry a jib and usually aaks' rigging was similar to rigging of coastal vessels. Large aaks, for example, Bonder, had two masts and the mizzenmast was placed in the back part of the deckhouse.