| 摘要 |
According to the invention a extendible and retractable luffing jib (13) is hingedly supported by a main boom (10,25) which can be positioned in a horizontal position, which luffing jib (13) protrudes at its rear side over some distance beyond the main boom (10,25), whereby a first block of sheaves (15) is fitted on the main boom (10,25) at a lower level than the luffing jib (13) while wire ropes (19,20) are reeved between these sheaves (15) and a second block of sheaves (14) mounted on the rear end of the luffing jib (13) for luffing the luffing jib (13) as well as for hoisting.
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