This would require tearing up the lift plan and starting again. The flow-on effect is that more counterweight, a closer setup location to the load, or a larger crane is required. The heavier hook block reduces the maximum weight of the load that can be lifted while keeping the crane within its rated capacity. To reduce line pull, a larger and heavier multi sheave hook could be required. Sometimes the crane and construction industries are faced with ‘client requirements’ that exceed current standards and regulations for both the percentage utilisation of the cranes chart AND the allowable line pull (usually in the order of 80-90%). Larger hook blocks or extra hook weights (also known as ‘cheek-plates’) add more weight to the total load lifted and therefore reduce the maximum load permissible under the hook. The choice of hook block needs to be considered in the lift plan from the start. As a guide we can also use the formula:Įxample: 30m of boom, 25mm rope, 5 parts of line This dead weight can be referred to as the minimum hook weight. Basically, the longer the boom and more line pull required for a lift, the more reeving of the rope required which effectively increases the dependence on a dead weight to assist the rope running effectively. So, how do we know how much weight is required on the hook? That depends on your crane configuration and the manufacturer’s recommendation first and foremost. When winching down with insufficient force to pull all the rope through the sheaves, the hook block may not lower initially, but instead drop suddenly creating a serious hazard for anyone underneath. In some cases, the hook block can strike the boom head causing considerable damage. A crane winch is designed to feed a rope out under tension, however, when the tension is not maintained between the winch and boom head due to insufficient hook weight or load, slack rope can accumulate at the winch.Īnother effect of insufficient hook weight is that the hook can be pulled up on one side, particularly if the operator is not smooth with the controls or winches up too fast before the multiple line parts can pass through the sheaves. Unwanted compressive loads causing a ‘birdcage’ effect or partial unravelling of the many strands that make up a rope can damage the rope to the point that a replacement is required. Wire ropes can be seriously damaged if they are used with insufficient tension or hook weight.
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