page_title: Chain boat
section_title: Drum winch
hierarchical_section_title: Chain boat / Drum winch
caption_attribution_description: English: Chain boat drive mechanism (drum winch)
context_page_description: 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 hauled by 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.
context_section_description: The older chain boats on the Elbe, the chain steamers on the Neckar and the three craft on the Main belonging to the Hessian Mainkette company used a drum winch to transfer power. In order to ensure the necessary traction on the chain on the driving drums, the chain was wound several times around two traction drums placed one behind the other in the centre of the boat. The chain ran in four to five grooves and was alternately wound over the front and rear drums.
  The disadvantage of this method was that the chain frequently broke. This did not simply occur due to the overloading of the chain by the length of the barge train. It has been calculated that even if the chain links wore down to half their original cross-section, this force would not have led to a break. Rather the problem lay in the fact that frictional wear on the forward traction drum was much heavier than on the rear. And once the diameters of the two drums became unequal, more chain wrapped around the after drum than could be handled by the forward one. This could produce tensions both on the drums and between them that were so large that the chain links could not withstand the tensile load and their fracture limit was exceeded.
  This effect became even more pronounced if the chain became twisted, e.g., the chain was pulled to one side or had even formed knots. This increased the turn radius by up to 25%, whereby the 5% elastic limit of the chain was reached.
  The transfer of tractive force from the drums to the chain was only achieved by friction. If frost or ice built up, the chain could slip. In such events, hot water was poured over the drums.
  Another problem with drum winches was the relatively large length of chain - 30 to 40 metres (100 to 130 ft) - that had to be wound several times around the two drums. If the chain boat was only used to haul barges upstream, it could not simply reduce the amount of chain needed for the drums on the way back otherwise, after a certain time, the surplus chain would pile up at the head of the operating section and there would be no slack at the start. In order to try and avoid this problem, the chain boat always carried the corresponding section of chain with it downstream and dropped it at the start of the chain route. As a result, there was a continual movement of the chain, that made control more difficult in more dangerous sections of the river, such as rapids. In particular, reinforced chain sections that were deliberately used, moved continually upstream. Also jettisoning the chain temporarily when two chain boats met was relatively difficult due to the multiple windings of the chain round the two drums.
  Many of the chain steamers without their own auxiliary engines had different gearing for moving upstream and downstream. When travelling upstream, it was designed for higher traction; when travelling downstream it was engineered for faster speed.
caption: Drum winch (1866)
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