Chain boat

A chain boat, chain tug or chain-ship was a type of river craft, used in the second half of the 19th century and first half of the 20th century on many European rivers, that made use of a steel chain laid along the riverbed for its propulsion. The chain was engaged using a steam engine mounted on board and enabled the boat to tow a string of barges. In Germany, such a boat was variously referred to as a Kettenschleppschiff, Kettenschlepper, Kettendampfer or Kettenschiff and in France as a toueur.

The chain was raised out of the water over a boom at the bow of the ship and led over the deck along the ship's axis to the chain engine amidships. The transfer of power from the steam engine to the chain was usually achieved using a drum winch. From there the chain was led over the deck to another boom at the stern and lowered once more into the river. By moving the stern boom and the two rudders, front and aft, from side to side it was possible to replace the chain in the centre of the river again, even when negotiating river bends.

Chain boat navigation revolutionised inland shipping during the Industrial Revolution in the second half of the 19th century in Europe and superseded the hitherto commonplace haulage of barges by draught animals or people. The chain drive of these riverboats made optimal use of still relatively low-powered steam engines of that period. In addition, the boats were especially well suited to the difficult condition of river navigation that pertained at that time: many rivers were shallow or fast-flowing and effectively precluded the use of paddle steamers. As a result, chain boats were soon being used on many rivers across Europe. But by the first half of the 20th century they were increasingly threatened by competition from ever more powerful paddle steamers, something that was aided by the canalization of rivers.

The first designs and early technical stages in the development of chain boats took place in the mid-19th century, especially in France. The prototype of all later chain boats on the rivers Elbe, Neckar and Main was the French steamboat La Ville de Sens, which was built by the German engineer, M. Dietz, around 1850 in Bordeaux, and plied the upper Seine between Paris and Montereau. Its technically very advanced operating principle and its engineering features were adopted by all the later European chain steamers.

The hull of these symmetrically-designed boats was almost level with the surface of the water at the bow and stern. This design reduced the power needed to lift the tow chain onto the bow of the boat and also reduced the draught at the bow. The greater height of the boat in the centre made it easier to accommodate the steam engine. This deck shape - low at the bow and stern, and higher in the centre - is typical of all subsequently built chain boats.

Chain boats were favoured on shallow rivers with fast currents. This was the reason for the flat, shallow draught of their keels. Chain boats optimized for particularly shallow water had a draught of only 40 to 50 centimetres (16 to 20 in) when unladen. Even fully laden with coal, their draught was only about 70 to 75 centimetres (28 to 30 in). This shallow draught enabled river transportation even in the dry summer months when the water level of rivers could be very low.

Shorter chain boats, with lengths from 30 to 40 metres (100 to 130 ft), and widths from 5 to 6 metres (15 to 20 ft), were more manoeuvrable and well suited to narrow rivers with many bends, for example on the Saale. Longer craft, with lengths from 45 to 55 metres (150 to 180 ft), and widths from 7 to 10 metres (25 to 35 ft), were better suited to relatively deep rivers such as the Elbe. The deeper a waterway was, the greater the power needed to lift the heavy chain. The bow of the ship was pulled down further. On larger boats this effect is reduced.

The hull itself was made of iron or wood and could withstand light impacts with the riverbed, and was compartmentalized internally by several waterproof bulkheads that prevented the craft from sinking in the event of a hole. Below deck were the steam engine, the coal bunkers and the crew accommodation.