- This paper describes the analysis of data from a three-year gross
time study of skyline, balloon, and helicopter yarding systems operating
in Western Oregon. Data collection activities were designed and supervised
by the Pacific Northwest Forest and Range Experiment Station, U.S.D.A.
Forest Service. The specific logging systems studied were running skyline,
North Bend standing skyline, long-span standing skyline, balloon (inverted
skyline, highlead, inverted skyline yo-yo, and highlead yo-yo), medium
helicopter, and heavy helicopter. These systems were observed under a
wide range of silvicultural and landscape design prescriptions, timber
type, terrain, and weather conditions.
The objective of this study was to develop yarding production
equations, to sumarize delays, road change times,and landing change
times, and to compare yarding production estimates made from both gross
and detailed time study data. This kind of information is useful for
the comparison of alternative logging methods in environmentally sensitive,
landscape-designed harvest units.
The data were segregated according to the individual logging
systems and analyzed via multiple regression. Then individual
system data were combined into the categories of short-span skyline,
long-span skyline, balloon, and helicopter. These combined data
were also analyzed via multiple regression. Chi-square tests were
performed to determine whether the equations developed from the
combined data were significantly different from the set of equations
developed from the segregated data. The results of these tests
support a conclusion, at the 95 percent level of fiducial probability,
that the equations developed from the combined data are as adequate
for predicting yarding production rates for these logging systems as
the equations developed from the individual-system data.
The variables shown statistically to influence yarding production
rates for all logging systems studied were yarding distance and
number of logs per turn. In addition, helicopter yarding productivity
was also found to be influenced by the type of cutting prescription,
and short-span skyline yarding, by chordslope. A variable combining
aspect and the season of work was found to be significant for both
the running skyline and the heavy helicopter.
Yarding delays were found to be affected by yarder, landing size,
season, and crews' experience. In order to compare similar systems'
delays, it was found important to segregate out weather-related delays.
In a separate study, detailed time studies were made on four
of the yarding systems analyzed in this paper. This allowed a comparison
between the measurements of yarding production rates made
during the detailed time study and those made during the gross
tinte study. The gross time study rates were consistently lower
than the detail time study rates. This suggests that the detailed
method does not reflect the total downtime as accurately as the
gross method. Thus the gross method appears better suited for
developing information that is useful for appraisal purposes and
the detailed method is better suited for evaluation of system