The effect of carriage type on yarding productivity and cost

The authors describe a study conducted under controlled conditions, with the goal of determining the eventual benefits of replacing the conventional clamped carriage with an unclamped motorized dropline carriage. The rigging was a classic three-cable configuration common to European yarder operations, with a single span standing skyline. The mainline and haulback line were used to move the carriage back and forth along the span. Two carriage types were used to gauge productivity and extraction cost differences between clamped (Hochleitner BW4000) and unclamped motorized dropline (SEIK Skybull 30/60) carriages. The authors conducted a classic time study, recoding work time, delay time and load size individually for 83 cycles. Replacing the standard clamped carriage with the unclamped motorized dropline carriage resulted in a productivity increase equal or larger than 30%. Extraction and processing cost decreased between 10% and 17%, depending on extraction distance. These results are valid for the specific set-up considered with the study, and may not be generalized without repeating the experiment under more varied conditions: however, they are very encouraging and may justify further investigations aimed at determining the effect of carriage type on fuel consumption and machine wear.