A Barge is a type of ship built since the 17th century. They are vessels with round bow and a long, narrow and shallow construction built and named 'barge'.
There are many different forms, and so there are 'subspecies' (amongst others: boltjalk, fairs and Eastern Sea Barge).
They were built of wood, iron and later steel. The iron barges were specifically for the Wadden Sea and coastal transport built and therefore were larger(80 to 140 tons).
The swords on the side, you need to keep ship on course. As a flatboat has very little depth you can not make good use of the resistance of the water. When there is wind from the side, you will be pushed aside very quickly. So you cross swords in the water to prevent it.