Automatically deployable load-line receiving mast structure for limiting deflection of proportionally extendable boom section crane

摘要

A proportionally extendable multi section boom crane is provided with an automatically erectable mast pivotally carried by one of the boom sections. The mast, which has a secondary sheave on the outer end thereof, normally rests in a stowed position adjacent the boom section on which it is mounted. The load line of the crane extending from the winch at the base of the boom section is trained over the secondary sheave, as well as sheave structure on the outermost end of the outer boom section. Elongated rod structure carried by one of the extendable boom sections outwardly of the crane has coupling means thereon engageable with the mast to initiate erection thereof after the proportionally movable boom sections have been extended a predetermined extent, normally after about 50% extension thereof. Passage of the load line over the mast in an erected position causes bending forces imposed on the extended boom by a weight suspended from the outermost end of the load line produces forces in opposition to the bending moment on the boom sufficient to prevent significant deleterious deflection of the boom from the longitudinal axis thereof.