Chains next took the place of hempen ropes, and between 1820 and 1830 many chain-tugs were employed on French rivers; but the first systematic service was carried out in 1846 between Paris and Montereau (65 miles) with tugs designed by Mr. Dietz, which in their essential features are similar to those in use at the present day. These tugs drew 18 inches of water, and were fitted with engines of from 35 to 40 horse-power, actuating the drum on which the chain was wound, two sets of gear being provided for going up and down stream, respectively. The boiler pressure was 5½ atmospheres, and the expenditure of fuel 5½ lbs. per horse-power per hour. Subsequently the chain was laid further up the Seine, and it was also applied to some rivers in France.
In Germany, in 1866, chain-tugs were running on 200 miles of the Elbe, and in the next ten or twelve years this system was in use on the Saale, the Brahe, and the Neckar.
The Elbe tugs are 138 to 150 feet long and 24 feet wide, with 18 inches draught. On the other rivers of Germany they are somewhat smaller. The sides are of ¼-inch iron plate, and formerly the bottoms were of ½-inch iron, but now they are built of 4-inch pine planks, as suffering less from abrasion on dragging over a rough bed. There is a rudder at each end, the wheel being amidships. The engines are from 60 to 70 horse-power, and work with a pressure of from 5 to 7 atmospheres. In slight currents a single drum is sufficient, the chain being kept pressed against it by rollers, and the drum is nicked to prevent the slip of the chain, but ordinarily there are two drums, to which the engine power is transmitted by two sets of gearing with different rates of speed—one for working up stream, with great power and small speed; the other for down stream, with less power and greater speed. Projecting over each end of the tug are booms furnished with guide-rollers for the chain, which give increased steering facilities.
The chains are from ¾ to 1 inch thick. When fractures occur, which is seldom, it is generally at the moment of the chain being first wound round the drum. Each drum is fitted with a brake, and at the ends of the booms there are clips, designed to prevent a running out of the chain in case of the brake failing to hold.
Chain-towing has so increased on the Elbe that in 1874 there were twenty-eight tugs running regularly between Hamburg and Aussig (420 miles). On the Neckar, at the same date, five tugs were employed on 56 miles of chain, and this was to be extended for 30 miles more, from Heilbronn to Cannstatt. Experience has shown that chain-tugs have great advantages over paddle-tugs, even in smooth water, for in the latter 60 to 70 per cent. of the power is lost in slips. Another advantage of chain-towing is that it produces no wash or swell. The charge for transport by this system is said to average about ¼d. per ton per mile.
In 1865 Mr. de Meseil, a Belgian, introduced a system of transport where a wire rope was substituted for the chain. The same system was taken up and improved by Max Eith of Wurtemburg, and worked with success on a 40-mile section of the Maas (from Namur to Liége). It was subsequently employed on canals in Holland and Belgium, and also on the Rhine. Extensive trials were also made on the Danube with satisfactory results.
A wire-rope tug company in 1873 laid down the line from Bingen to Rotterdam, but worked the upper section only themselves, viz. from Bingen to Ruhrort (155 miles). From Ruhrort downwards a concession was granted to a Dutch company, who employed a special kind of tug, in which the rope passed over drums inside the vessel, similar to the chain-tug system; but the usual arrangement of having the rope outside the tug has been found most convenient, as it enables it to be easily cast off and taken up again when two tugs meet.
The wire rope generally used on the Rhine is formed of forty-nine wires 0·189 inch thick, is 1·7 inch in diameter, and weighs 4¾ lb. per yard. It usually costs 10 d. per foot, which is about one-third the weight and cost per foot of an iron chain of equal strength.
The first wire-rope tugs at work in Holland and Belgium had a 20 horse-power engine for the driving wheels, and another 10 horse-power engine to work a screw when going down stream clear of the rope. At each end, outside the tug, there are guide-wheels to keep the rope clear of the vessel, and at the centre are two large wheels which lead the rope on to a Fowler’s clip-drum, against which it is kept pressed by small rollers. To pick up the rope and pass it over the wheels and drum takes a quarter of an hour.
The Danube Company’s tug Nyitra, which resembles the Rhine tugs, is 140 feet long, 24½ feet wide, and draws 3½ feet of water; the clip-drum is 10½ feet, and the adjoining wheels about 9 feet, in diameter. Against a current of 4¼ feet per second, it can draw eight barges, with a total load of over 2000 tons, at a speed of 3 miles an hour, with useful effect of 75 per cent. In chain-tugs this percentage is higher on account of the greater flexibility of the chain. Fractures of the rope seldom occur, in spite of the rocky bottom in certain sections of the river. The life of a wire rope may be taken at from four to six years.