Cabling in multiple fall ropes of lifting systems for deep water

Cabling is the metastable twis~ng together of multiple falls of rope caused by torque in the ropes induced by the applied tension, but resisted by the indination of the ropes to the vertical. Conventional analysis of cabling assumes that rope tension is uniform, ropes are straight from the point of suspension to a sheave at the hook, and rope separation is the same at the top and the bottom. When, as in deep water operations, the weight of the rope results in a tension gradient from top to bottom, not only must a different approach be adopted in calculating rope torque, but the rope no longer falls in a straight line: it is a catenary. A further complication arises when, in an attempt to improve the resistance to cabling, the rope spacing is increased at the top. This paper addresses all these issues, explaining how to analyse this important problem.

Author: C.R. Chaplin