Through the courtesy of the Engineering News of New York, the Review is enabled to present a complete description and a few very clear illustrations of the dipper dredge PAN-AMERICAN, recently completed for Hingston & Woods of Buffalo, N. Y., for use on the great lakes. This is claimed to be the largest dredge of its type ever constructed. It has a dipper with a capacity of 8 1/4 cubic yards or about 12 tons. While intended for service on the great lakes, the dimensions of the hull are such that the dredge can go through the Welland and St. Lawrence canals and can easily be fitted with tanks for salt water service. The hull and general arrangement of the dredge were planned by Mr. William E. Hingston, and the machinery was designed and built by the Bucyrus Co. of South Milwaukee, Wis. The Engineering News acknowledges indebtedness to Mr. Hingston and to Mr. A.W. Robinson, M. Am. Soc. C.E., chief engineer of the Bucyrus Co., for the information from which this description has been prepared.
The hull is built of white oak and Oregon fir, and is 136 feet long 42 feet 3 inches beam, and 13 feet 6 inches deep. There are four longitudinal steel trusses. Two of these are spaced 26 feet apart, or on the line of the cabin work, and are each 119 feet long and 25 feet high. The total height from the keel to the tops of these trusses is 32 feet. The other two trusses are located at the sides and are each 119 feet long and 13 feet deep, or just the depth of the hull. The sides of the hull are 8 inches thick, and the bow is 12 inches thick. The bottom and sides are connected by 136 wrought-iron knees. Altogether, including the material in the spuds, there entered into the construction of the hull 157,000 feet B.M. of fir, 70,000 feet B.M. of oak and 23,000 feet B M. of pine, or a total of 250,000 feet B.M of timber.
There are four spuds, two at the bow, each 4 by 4 feet, made up of four 24 by 24 inches Oregon fir timbers, 50 feet long, and two at the stern 2 by 2 feet in size. The bow or forward spuds are raised and lowered by power from the main engine by means of wire ropes. There is a large sheave on top of the spud and another fitted in a slot through the spud about 12 feet from its lower end. There are two ropes to each spud, both connected to opposite ends of one drum, and the ends of the rope are attached to a fixed point outside the spud, and provided with means for adjustment. The rope passing around the sheave near the lower end of the spud serves to raise it, and the other rope passing over the top of
the spud serves to force it down with great force and thus "pin up" the dredge.
It will easily be seen that with dredges of the dipper type it is very necessary to pin them up securely, so that a considerable portion of the weight of the hull at the forward end rests upon the spud upon the bottom, in order to hold the dredge against the digging thrust of the dipper. The "pinning up" power of the Pan-American is easily able to lift the end of the hull with all of its machinery upon it 2 feet in the water, which is equal to sustaining a weight upon the spuds of about 130 tons. When the spuds are off the bottom the hull is "down by the head" several feet due to the great weight of the machinery on the front end. In other words no attempt has been made to distribute the weight upon the hull so that it will float on an even keel. In fact it would be a disadvantage to do so, as the extra weight is needed at the forward end to hold the spuds down, and when the dredge is pinned up she is in the best position for work. The A-frame and boom are of steel, and are clearly shown in the view of the front end of the dredge. The A-frame is 53 feet high, and the boom is 53 feet long, and weighs 30 tons. The dipper handle is of wood, reinforced with steel plates, and, as already stated, it carries a dipper of 8 1/4 cubic yards capacity and weighing 16 tons. As the dipper is operated by wire rope, single whip, it is expected that the dredge will work very rapidly. She is guaranteed, in fact, to make a full revolution with a load from water 25 feet deep every 40 seconds, which is a capacity of from 5,000 to 6,000 cubic yards per ten-hour day.
Perhaps the most distinguishing feature of the dredge is the use of the single-part wire-rope hoist instead of the chain hoist for the dipper. The reason for this innovation, as stated by the builders, is as follows. As dipper dredges increase in size a hoisting chain that will withstand the necessary strain becomes exceedingly heavy, and it is also necessary to run it at great speed in order to make time. This necessitates a great waste of power and wear and tear of the chain and sheaves. A hoisting chain, to do the work of this great dredge, would be three parts 2 ½ inches in diameter and 275 feet long, and would weigh about ten tons. It would require four sheaves, which should not be less than 6 feet in diameter, and would probably weigh about two tons each, or a total of eight tons. It will readily be seen that the friction and wear and tear on this chain would be enormous, and the horse power required to move it would be considerable. Moreover, when such a chain breaks, as it sometimes does without notice, it is a serious task to fish it up again. So much for the disadvantages of the chain hoist for very large dredges.
Attempts have been made to substitute wire rope for chain by using three parts of rope and binding them around the sheaves in the usual way, but this method has not been altogether satisfactory, as the frequent bending and friction of the ropes against each other caused them soon to wear out. In 1890 Mr. John Kennedy, chief engineer of the harbor commissioners of Montreal introduced the first wire rope dredge for large and heavy work on the single rope plan. This dredge was designed for digging hard material such as shale rock, etc., in 40 feet of water, and had a direct pull of 120,000 pounds. results obtained with the dredge were highly satisfactory, and three others have since been built which are almost its exact duplicates. It has been found that these dredges all possess exceptional speed of working, as compared with chain dredges, especially in deep water for the reason that the dipper can drop so much more freely with the direct wire rope than is the case when it is required to overhaul three parts of chain. With the wire rope it falls almost with the speed due to gravity, being restrained but slightly and checked up at the right moment as it nears the bottom, whereas with the chain its descent is comparatively sluggish.
Another incidental advantage of the wire rope over the chain is the angle of lead of the pull upon the dipper. It will readily be seen that it is desirable to have this lead as far out as possible in digging, in order that as large a component of the strain as possible may go into a push upon the scoop and not into compression of the dipper handle. In the case of the PAN-AMERICAN, the lead of the rope is 20 per cent. further out on the boom than it' the usual three-parts chain were used for the same length of boom. This is due to the fact that a single sheave of large diameter is used at the extreme point of the boom, instead of two sheaves, mounted as usual, back of the end of the boom. An additional advantage of the wire rope over a chain is that, after it becomes worn, it gives warning of a break by some of the wires breaking. In this way its failure is a gradual one and gives opportunity to replace the rope, which can be done very quickly. A chain, on the other hand, breaks without warning, and lets the dipper and a large portion of the chain go to the bottom, and in such large machines it requires many hours work and delay to raise and repair.
The hoisting rope of the PAN-AMERICAN is extra flexible plow steel, 2 ½ inches in diameter, and turns over sheaves 8 feet in diameter. It is operated by an 18 by 24 inch double high pressure engine, a general view of which is also printed herewith. It will be seen that the engines are of very substantial construction, having the drum and gearing all self-contained in one pair of frames. The mail, hoisting gears are 12 feet in diameters 12 inches face, and 4 ½ inches pitch, and power is applied to them by means of a steam thrust operating two band frictions. The friction bands are 12 inches wide and are lined with wood blocks, and the friction housings are also of cast steel, turned to a perfectly smooth surface. The steam cylinder for applying the friction is so designed that the power can be applied gradually and slipped to any desired degree. This is done by special arrangement of the valve motion, whereby the movement of the plunger connected to the cylinder follows the movement of the hand on the operating lever and coincides with it. Besides the main hoisting engine there are a 10 by 14 inch double swinging engine and a 9 by 12 inch double hacking engine. A separate engine runs the electric plant, and there are a number of steam thrust cylinders for various operations. In fact the whole of the more important operations of the dredge are controlled by steam so that the labor of the operators is reduced to a minimum. The builders assert, in fact, that despite its great size this dredge will be handled with less physical effort than most small old-style machines. Steam is supplied to the various cylinders by a pair of 8 ½ by 12 inch return-flue marine hollers operating under 150 pounds steam pressure. These boilers were built by Farrar & Treffts of Buffalo N.Y. The coal bunkers have a capacity of 150 tons. To indicate further the accommodations of the dredge, it may be stated that she is provided with state rooms office, bathroom, and a dining room for forty persons and is lighted by electricity throughout. The PAN- AMERICAN is now at Portage Lake, where her owners have a large contract for dredging.
The Marine Review
July 27, 1899