An analysis of forces and conditions which influence the successful passage of a carriage over an intermediate support jack during downhill multi-span logging

Abstract

In this paper, a catenary analysis of static skyline, mainline and haulback cable tensions just prior to an unsuccessful attempt by a carriage to pass an intermediate support jack is presented. Field tests were conducted for a range of skyline deflections and span chord slopes. Data collected during the field tests included static and dynamic cable tensions and cable geometry. The relationship between upper span skyline deflection, the percent change in span chord slopes, and their influence on successful carriage passage was determined. During the field tests it was observed that maintaining a taut haulback as the carriage passed the support jack prevented the carriage from surging out of control and reduced dynamic tension fluctuations. It was also observed that yarding the loaded carriage uphill over the support jack was prohibited by skyline deflections which still allowed successful carriage passage for the downhill yarding configuration.