| 摘要 |
A double-topping type derrick crane is operable continuously throughout 300 degrees of azimuth turning of its boom to serve two loading areas forward and aft of the crane. This is made possible by a multiple-swivel, universal coupling mechanism between the two topping tackles and the boom top, this mechanism permitting one topping tackle to flip over the other, whereby the relative positions of the tackles are automatically inverted without mutual contacting or entwinement of the topping tackles.
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