Lakes Michigan and Erie. The most important docks on the former lake are at Milwaukee, South Chicago, Indiana Harbor and Gary, and those on the latter lake are at Detroit, Toledo, Sandusky, Huron, Lorain, Cleveland, Fairport, Ashtabula, Conneaut, Erie and Buffalo. See Figue 1. These docks, so far as piers are concerned, are mostly of the same general type, all being of sufficient length to accommodate at least one boat and having a dock wall with a vertical face, the top of which is from 5 feet to 12 feet above mean low water level. The mechanical unloaders move along the dock on tracks and are so arranged that the buckets can be extended over the boats and lowered into the hatches and when full, hoisted and moved back over the dock, where the ore is dumped into cars, onto stock piles or into ore troughs, and in some cases they are arranged so as to transfer the cre from the stock piles or ore troughs to cars. When the furnaces are located at the docks they are called furnace docks, but when the ore has to be hauled by rail from the docks to interior furnaces the docks are known as railroad decks. It can be readily understood that the digging and raising of the ore out of boats, placing it on cars or depositing it on stock piles, which is done at the unloading piers, is a much more complicated operation than the mere dumping of the ore by gravity from the cars to bins and then to the boats, as in the case of loading docks. In the latter case practically no machinery is required except for operating the gates and chutes, but in the case of the unloading decks all work is done by ore handling machinery of more or less complicated construction and of many different designs representative of this class of machinery for performing the special work required of it. The special machines are designed for the following kinds of work: (a) For transferring the ore from the boats to cars only. (b) For transferring ore from boats to cars, also to ore troughs or piles. (e) For transferring ore from boats to ears, ore troughs or piles and also from the troughs and piles to cars. FIG. 7-One 15 ton Electric Bridge. Six 6 ton Electric Unloaders. Concrete dock and Trough. By Hoover and Mason, Chicago, Ill. (d) For transferring ore from boats to cars, stock piles or bins at furnace docks. (e) For transferring ore from troughs or piles to cars or bins, but not for unloading boats. In addition to the above named machines there are a number of small machines such as whirleys, revolving derricks, locomotive cranes and steam shovels used on various docks to transfer ore where the quantities to be moved do not justify the operation of the big machines. These whirleys consist of derricks which can be revolved in a horizontal plane and are equipped with clamshell buckets, suspended from and operated by wire ropes. The derrick is mounted on a car containing the boiler and machinery and can move along the dock by its own power. Locomotive cranes differ from the whirleys only in size, being much smaller, and run on standard gauge tracks, while the whirleys run on tracks spaced 14 to 18 feet center to center. The greatest average unloading capacity of any dock is about 2,000 tons per hour and the total average of all the unloading docks in a 10-hour day is over 300,000 tons, or more than 600,000 tons in a 20-hour working day. Some of these docks have unloaded boats at the rate of over 2,500 tons per hour. If they should operate for 200 ten-hour days in a year they would have a capacity of 60,000,000 tons, which is about equal to the amount of ore unloaded at these piers during the past year, but of course by working twenty hours a day instead of ten they can handle double this capacity. It will be observed that the capacities of all the docks used for unloading boats are about the same. as those for loading them. The cost of operating an unloading dock will vary with the conditions as to output and capacity, class of boats delivering the ore, length of the dock as it affects the cost of the dock wall and runways for the cre handling machinery, maintenance, interest on investment, etc., the width of the dock as it affects the distance the material must be handled, and the kinds of machinery used. The location of the yard also has an ultimate effect on the cost as it affects the amount of engine service |