During the work on digging a short cut in the Kongeå river in 1945, the machine hit a structure of sturdy wood. Some of the timbers were salvaged, and three of them brought to the museum in nearby Ribe, where they initially were interpreted as parts of a bridge.
In 1964 they were recognised as ships timbers, and sent to the National Museum of Denmark for documentation and analysis. Untill then the find spot was only very roughly known, but at this time one of the workmen from 1945 reported more details. The timbers had been found by the village of Gredstedbro, about 6 km east of the mouth of the Kongeå rivers in the Vadehavet between the islands Fanø and Manø. A search for the ship was then launched, but failed to relocate it.
The find consisted of a frame, a stem or sternpost fragment and a part of the keel. All were made from oak that had retained its shape astonishingly well without any conservation treatment. The frame was made from one naturally V-shaped piece of wood. One of the arms was well preserved, while the other had broken off. The well preserved side had notches for 7 clinker strakes, the other only three. About every second notch had a 2.5 cm hole with a treenail for fastening of the planks. The surfaces in the notches were cut at an angle, which means that the frame had been placed near either the stem or stern. The frame had a tear-drop section minimizing the contact beween the frame and the planking. Above the keel the frame was 26 cm moulded and 12 cm sided, while the preserved length was 1.8 m. The original length of the arms must have been 2.2 - 2.3 m.
The stem or stern fragment was 1.13 m long. Its lower end consisted of a horizontal scarf like the one in the Nydam ship, while the upper was broken off. Along the inner edge was a rabbet 1.8 cm deep and 4 cm wide. In the rabbet were holes from the nails which had kept the garboards in place. The distance between them was 19 - 21 cm.
The keel fragment was 2.03 m long and broken lengthwise along the centre line. Along the preserved outer edge was a rabbet, 1.8 - 2 cm deep and 5 cm wide, with clinker nail holes spaced 18.5 - 20.5 cm. Original dimensions of this part of the keel had been a width of 16 cm and a height of 10 cm - i.e. a wide and low keel. The underside was very worn, which indicates that the ship had often been pulled ashore.
The dimensions of the timbers are similar to those of the Nydam ship, and thus the ship itself might have been of comparable size, roughly 20 - 25 m long.
The Gredstedbro ship could have complete when found, but how much of it has been left remains an open question.
The dating of the treenail from the Gredstedbro ship to 610 AD, confirms the typological dating without narrowing it. The C14 dating of the treenail to 610 AD has a margin of 100 years to each side, and here it is important to realise that this only dates the time of growth. Thus it is impossible to date the building of the ship more closely than between 600 AD and 800 AD.
The tear-drop section of the frame is a feature that points back in time to the Nydam ship and the oldest Viking ships known from the Norwegian burial monds. Differently from these the fastening of the frames to the planks was here done with treenails, though in a very irregular pattern, leaving about half of the notches without fastenings.
The stem or sternpost fragment from the Gredstedbro ship also shows similarities with the Nydam ship. The lower end terminates in a horizontal scarf, whereas the keel scarves known from the Viking Age are all vertical.
The keel also shows an "old-fashioned" design with its low and wide section. The ships from the Viking age and later have a higher and narrower keel better suited for countering the leeway from the sail.
The Gredstedbro ship must typologically be placed between the Nydam ship and the Viking ships. Some constructional features point back in time, while the treenailing and the notches for the strakes are "modern". On the basis of the scanty timbers available today, it is difficult to discribe the original vessel. But the similarity with the Nydam ship suggests that the Gredstedbro ship was a large and presumably seagoing rowing ship. Seen from a distance it resembled the Nydam ship from ca. 315 AD more than a square sail rigged Viking ship from the 9th century.