- Han, Han-Sup
University of Maine
The process of selecting a cable logging system must take into account all identified physical and economic constraints so that the system proposed is operationally feasible under most situations that are encountered. The constraints were designed to reflect such study area features as yarding direction, yarding distance, payload, intermediate support, turn size, yarder drum capacities and carriage requirement. Three roads were developed in two management units so that yarding distances would stay within 400m. Twenty-eight profiles were created and reviewed. Since most slopes were convex and, hence, required intermediate supports, only a standing skyline system was further analyzed for implementation. Fifty-nine yarders for standing skyline systems were classified into three categories: small, medium and large. Taking into account the properties of the majority of yarders in each of the classes, yarder features were outlined to represent the average yarder in each category.
Under the constraints identified, the payload analyses were conducted by LOGGERPC V3.0. Payloads were evaluated for both yarding directions, for each yarder size and various intermediate support heights. The downhill yarding analyses were inclined to achieve higher payloads. However, the differences between uphill and downhill yarding in achievable payload were not significant. Therefore, considering the disadvantage of downhill yarding, uphill yarding is more desirable when an access road is available at the top of profile.
Payload capacities were adapted to the most restrictive criteria in selection of an optimal yarder because payloads determine the turn size and, hence, productivity. Payload analyses showed that the small yarder did not satisfy the minimum payload requirement (1,000 kg) in more than half of the analyses, while the large yarder achieved greater than the maximum payload (5,000 kg) in 65% of all analyses. However, the medium yarder accomplished the desired payloads (1,000-5,000kg) with greater than the maximum payload in 36% of all analyses. Therefore, considering greater rigging and higher initial costs associated with the large yarder, the medium yarder is best for these areas.
Medium yarders were characterized by a wide range in tower height. To analyzed the effect of the tower height, the range was divided into two classes; 9-15m and 15-18m. The lower tower (9m) achieved increased payloads. These increases were significant and prevailed in more than half of the analyses. All results indicated that the medium yarder, having a 9-15m tower was optimal for study areas.