GB656878A - Improvements in and relating to a mast structure - Google Patents

Abstract

656,878. Erecting portable derricks. MOORE CORPORATION, L. C. Oct. 9, 1947, No. 27134. Convention date, Oct. 9, 1946. [Class 78 (iv)] The mast structure 1 of an oilwell derrick is hinged at 4 by its front legs 3 to a base 2 and is raised by a sling connected to a gin pole 9, 11 on the base and to the travelling block 24 of the lifting tackle operated by a line 21 passing over a sheave 19 on the gin pole and over the crown block 23 from a winch 22. The sling comprises a doubled length of cable 29 passed over the lifting hook, around laterally spaced sheaves 30 on the mast, and either secured to a transverse tube 18 at the upper end of the gin pole 9, 11 or, for a tall mast, passed over laterally spaced pulleys 37 at the upper end of the gin pole to be connected at 39 to the rear legs 7 of the mast. As shown in Fig. 4, each pulley 37 is mounted on a pin 34 supported in bearing arms 31 joined by plates 32 and removably secured by bolts 33 to a bracket 26 rotatably secured to the transverse tube 18. For hoisting a small mast the pulleys 37 are removed and the sling connected directly to members 28 secured to the brackets 26. When the mast is erected the inclined braces 8 lie alongside the front legs 9 of the gin pole and the bottom ends of the rear legs 7 of the mast are directly above the top of the gin pole. In an alternative fixture for the sling 29 at the top of the gin pole, a pair of pulleys is permanently mounted on the crosstube 18 and the sling may be passed around the pulleys, or secured by a bracket directly to them. U.S.A. Specification 2,271,578 is referred to.