ROPE PULLEY FRICTION BRAKE.
The leading dimensions of the eight wire rope tugs now worked by the company are as follows:
Tugs No. I. to Tugs No. V. to
IV. VIII.
Meters. ft. in. Meters. ft. in.
Length between
perpendiculars 39 = 126 0 42 = 137 10
Length over all 42.75 = 140 3 45.75 = 150 1
Extreme breadth 7.2 = 28 8 7.5 = 24 5
Height of sides 2.38 = 7 11 2.38 = 7 11
Depth of keel 0.12 = 0 5 0.15 = 0 6
All the boats are fitted with twin screws, 1.2 meters (3 feet 11¼ inches) in diameter, these being used on the downstream journey, and also for assisting in steering while passing awkward places during the journey up stream. They are also provided with water ballast tanks, and under ordinary circumstances they have a draught of 1.3 to 1.4 meters (4 feet 3 inches to 4 feet 7 inches), this draught being necessary to give proper immersion to the screws. When the water in the Rhine is very low, however, the water ballast is pumped out and the tugs are then run with a draught of 1 meter (3 feet 3 3/8 inches), it being thus possible to keep them at work when all other towing steamers on the Rhine are stopped. This happened in the spring of 1882.
Referring to our engraving, it will be seen that the wire rope rising from the bed of the river passes first over a large guide pulley, the axis of which is carried by a substantial wrought iron swinging bracket, this bracket being so pivoted that while the pulley is free to swing into the line on which the rope is approached by the vessel, yet the rope on leaving the pulley is delivered in a line which is tangential to a second guide pulley placed further aft and at a lower level. This last named guide pulley does not swing, and from it the rope is delivered to the clip drum, over which it passes. From the clip drum the rope passes under a third guide pulley; this pulley swings on a bracket having a vertical axis. This third pulley projects down below the keel of the tug boat, so that the rope on leaving it can pass under the vessel without fouling. Suitable recesses are formed in the side of the tug boat to accommodate the swinging pulleys, while the bow of the boat is sloped downward nearly to the water line, as shown, so as to allow of the rising part of the rope swinging over it if necessary.
The hauling gear with which the tug is fitted consists of a pair of condensing engines with cylinders 14.17 inches in diameter and 23.62 inches stroke, the crankshaft carrying a pinion which gears into a spur wheel on an intermediate shaft, this shaft again carrying a pinion which gears into a large spur wheel fixed on the shaft which carries the clip drum. In the arrangement of hauling gear above described the ratio of the gear is 1:8.44, in the case of tugs Nos. I. to IV.; while in tugs Nos. V. to VIII. the proportion has been made 1:11.82. In tugs I. to IV. the diameter of the clip drum is 2.743 meters (9 feet), while in the remaining tugs it is 3.056 meters (10 feet).
From some interesting data which have been placed at our disposal by Mr. Thomas Schwarz, the manager of the Central Actien-Gesellschaft fur Tauerei und Schleppschifffahrt, we learn that in the tugs Nos. I. to IV. the hauling machine develops on an average 150 indicated horse, while in the tugs No. V. to VIII. the power developed averages 180 indicated horse power. The tugs forming the first named group haul on an average 2,200 tons of cargo, contained in four wooden barges, at a speed of 4½ kilometers (2.8 miles) per hour, against a stream running at the rate of 6½ kilometers (4.05 miles) per hour, while the tugs Nos. V. to VIII. will take a load of 2,600 tons of cargo in the same number of wooden barges at the same speed and against the same current. In iron barges, about one and a half times the quantity of useful load can be drawn by a slightly less expenditure of power.
The average consumption of coal per hour is, for tugs Nos. I. to IV., 5 cwt, and for tugs Nos. V. to VIII., 6 cwt.; and of this fuel a small fraction (about one-sixth) is consumed by the occasional working of the screw propellers at sharp bends. The fuel consumption of the wire rope tugs contrasts most favorably with that of the paddle and screw tugs employed on the Rhine, the best paddle tugs (with compound engines, patent wheels, etc.) burning three and a half times as much; the older paddle tugs (with low pressure non-compound engines), four and a half times as much; and the latest screw tugs, two and a half times as much coal as the wire rope tugs when doing the same work under the same circumstances. The screw tugs just mentioned have a draught of 2½ meters (8 feet 2½ inches), and are fitted with engines of 560 indicated horse power.
During the years 1879, 1880, and 1881, the company had in use fourteen paddle tugs and ten eight-wire rope tugs, both classes being--owing to the state of trade--about equally short of work. The results of the working during these years were as follows:
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| | Freight | Cost of | Degree
| | hauled | haulage in | of
Class of tugs. | Year. | in | pence per | occupation.
| | ton-miles. | ton-mile. |
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Paddle | 1879 | 31,862,858 | 0.1272 | 0.686
" | 1880 | 31,467,422 | 0.1305 | 0.638
" | 1881 | 28,627,049 | 0.1245 | 0.537
Wire Rope | 1879 | 15,407,935 | 0.1167 | 0.614
" | 1880 | 17,289,706 | 0.1056 | 0.615
" | 1881 | 17,593,181 | 0.0893 | 0.536
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