During a recent Nippling Down and repositioning of the 21 ¼ BOP from the wellhead to the stump the BOP Winch Line (the overhead crane) parted allowing the top of the BOP to fall towards the broken line direction. Fortunately the BOP had not been lifted high and the bottom of the BOP lodged in the ground preventing it from flipping over. The other overhead crane cable was unaffected and a safety sling was fitted to this unit as an extra precaution while it was taking all the weight. There was no injury to personnel. There was however damage to flexible control hose from the HCR to the choke manifold requiring the hose to be replaced.