Ring supported mobile tower crane

A ring supported mobile lift crane comprising in combination, lower works including a supporting frame and self-propelled transport means, a ring defining track mounted on said frame and transport means, upper works mounted above said frame for rotation with respect thereto, a load carrier extending from said upper works in riding contact on said ring, a counterweight carrier extending oppositely from said upper works in riding contact with said ring, a tower mounted on said load carrier for pivotal movement between generally horizontal and vertical positions, a boom pivoted to the outer end of said tower, a rearwardly inclined mast mounted on said load carrier and connected to said upper works and said counterweight carrier by rigging means, a tower backstay connected to the top of said tower and through tower hoist rigging to the top of said mast, a fixed boom strut connected at one end to the top of said tower and at the other end to a first fixed pendant secured to said load carrier so that said tower, said fixed boom strut and said first fixed pendant form a first fixed triangle, a movable boom strut connected at one end to the top of said tower and at the other end to a second fixed pendant secured to the outer end of said boom so that said boom, said movable boom strut and said second fixed pendant form a second fixed triangle, means including a boom hoist line interconnecting the outer ends of said fixed and movable boom struts for raising and lowering said boom, and means for changing the length of said tower hoist rigging for raising and lowering said tower, boom, boom struts and tower backstay as a unit.