7 Harvest System Capabilities

7.1.1 Ground Based Systems

This particular harvest system will be used in terrain that falls within the zero to thirty percent slope class. In some specific situations within our project area however, we classified some areas that had side slopes of up to 40 percent as ground base operations. As with all ground operations, the terrain in the area limits what ground equipment we can use. In the uphill situation, the machine horsepower is the limiting factor, while in the downhill situation, operator safety and production become the limiting factors. When yarding downhill, if the slope is too steep, the logs being yarded are very hard to control. This in turn causes production delays when the operator has to get out of the cab and free a hung up turn. The following table shows the conditions under which each piece of equipment can operate:

7.1.2 Cable Yarding Systems

Cable systems are limited less by the percent slope and more by shape of the ground you are working in. These systems are best suited for areas where the slopes fall between 30% and 100+%. The major limiting factor is shape of the landscape. A ground profile can be classified as concave, planar, or convex. The ideal ground profile is highly concave. This allows for the greatest deflection, and therefore the highest payloads. The worst case profile is highly convex. This ground shape affords little or no deflection and therefore payloads tend to be uneconomical. In the planar case, deflection can usually be found, but most times this requires rigging a tailhold tree 30-50 feet high. Within our project area profiles were analyzed for both central landings using a 72 foot Madill tower and mobile landings using a 60 ft. Madill 124.

7.1.3 Helicopter Based Systems

The major benefit of helicopter systems is that they don't need road access into the harvesting unit. This can be a huge benefit in steep, remote areas where road building is too costly or physically unfeasible. There are several areas within our project boundary that fall within this category. However, there are many limiting factors with helicopter yarding such as its large landing size requirement, and its tremendous cost. A helicopter landing must be at least four acres in size in order to accommodate both the landing/decking of logs as well as the refueling of helicopters. In addition, a helicopter operation usually falls between $3000 to $3500 dollars an hour. Helicopters are also limited by their external yarding distance with a maximum external yarding distance of approximately one mile. Regardless, as mentioned above, there are several areas in our project that will require helicopter yarding if timber is to be extracted out of these zones.

In order to perform a cost and production analysis on the settings that were developed for the North Tahoma planning area, both skyline yarding and mechanized ground systems had to be analyzed. Since Region 6 of the National Forest Service had already developed a spreadsheet that calculates cost and production for both of these systems, this proved to be our main source of estimation.

There were many input variables that first had to be calculated in order to perform this analysis. Many of these variables were the same for both cable and ground based systems. These included the following: net volume per setting, setting acres, percent slope to landing, average yarding distance, average piece size in board feet and wood weight. We determined volume per setting by multiplying the volume per acre by the acreage of the setting. The volume per acre was derived in LMS for each stand type and then an AML (arc macro language) was used to calculate the volume per acre for each setting. The setting acreage was derived in GIS.

An average value of 25 and 40 percent slope to landing was assigned to ground based and cable systems, respectively. Average yarding distance was calculated with an AML. Average piece size was determined by dividing board feet/acre by trees/acre (also derived in LMS), which gave board feet/tree. We then divided this value by three assuming there were three logs per tree at a 40 foot length each. A wood weight of 11 lbs/bf and 10 lbs/bf was used for western hemlock and Douglas fir dominated stands, respectively.

In addition, both cable and ground based systems had their own independent variables. Cable systems include the following: number of sky roads, road change time (min), payload (net lbs), road spacing (ft), outhaul speed (ft/min), lateral inhaul speed (ft/min), effectiveness (min/hr), mainline tension (lbs), move in time (hrs) and distance (miles), rig up time (hrs), unrig, move, and rig up (hrs/landing), rig down (hrs), move out time (hrs), and tail tree anchor height (stump or tailtree).

The number of sky roads (yarding corridors) was determined only for units that may either be yarded through cable systems or helicopter. We classified these as dual units and took random samples in order to generate relationships between the number of corridors and a more easily derived quantity.

For central tower settings, a strong relationship (R2 = 0.9) was found between the angle of the yarding corridor span and the number of yarding corridors (assuming 150 foot spacing between corridors). The angles for each central tower setting designated as a dual unit was measured and the relationship was then used to project the number of corridors. For mobile tower settings, a relationship (R2 = 0.6) was found between the perimeter of the setting (derived in GIS) and the number of corridors. This relationship was used to estimate the number of corridors for each of the mobile tower settings designated as dual units.

Road change time was assumed to be 50 minutes. Payloads for settings were calculated in LMS and confirmed in PLANS. A QMD and average height was determined from LMS for each stand and then interpolated into each setting with an AML. Road spacing was set at 150 feet due to line capacity for a given yarding carriage. Both outhaul and lateral inhaul speeds were taken directly from manufacturing specifications. Effectiveness was set at 50 minutes per hour due to delays and other hang ups in the operation (10 minutes of delay per hour). Mainline tension was set at the maximum safe working load for the given line diameter being used.

Move in/move out time and distance were set at a standard 8 hours and 60 miles for both tower yarders. These numbers are only rough estimates and would have to be changed according to the actual unit sale when it comes online for more accurate cost estimation. We assumed that there were on average 3 settings per unit, so the actual move in time and distance per setting were set to 2.7 hrs and 20 miles, respectively. Rig up time and rig down time were assumed to be the same and were set at 6 hours/unit for the large central tower yarder and 2 hours/unit for the mobile tower yarder. Unrig, move, and rig up time for the central tower was set at 8 hours and 4 hours for the mobile tower.

Tailtree anchor height was determined in PLANS and GIS. If the majority of the setting was able to be yarded with an anchor height at stump level, then this was what was used; otherwise, anchor height was set as a tailtree designation. For the central tower, a larger cable diameter for the anchor was used as opposed to the mobile tower. In addition, there were also on the ground workers who included choker setters, chasers, rigging slingers, hook tenders, yarder engineers, loader operators, and delimber operators. These figures as well as the equipment being used can be seen in the following Table 7.2, Specifications for Central and Mobile Tower Settings Harvest Cost and Production. Hand falling and bucking was assumed in all situations.

For ground based operations, equipment included a feller buncher, track skidder, a log loader, and a delimber. This combination was used since most of the settings with a dual designation had an EYD over 400 feet which is the maximum distance for shovel yarding.

Independent variables for production in ground based operations include number of yarding machines, pieces per turn, delay time/hour (%),additional delay time per turn (min), harvester boom length (ft), average number of cut trees/ac, average cut tree height (ft), merchantable volume per cut tree, process time (min/tree), search time (min/tree), weave factor (%), and average cut tree DBH.

Several assumptions had to be made for these variables, which can be found in Table XXX, Specifications for Ground Based Settings Harvest Cost and Production. Stand information such as trees/ac, tree height, DBH, and merchantable tree volume were averaged from highly variable values determined for each stand in LMS. Harvester variables including boom length, process time, search time and weave factor were estimated from harvester information and typical range of values offered in the costing spreadsheet.

Labor costing for ground based harvesting included operators for loaders, feller-bunchers, limber buckers, and skidders. Move in/out data was similar to that used for cable operations, minus the time required for rigging the towers.

After all variables had been inputted into the spreadsheet, cost and production estimates could be calculated. Outputs included MBF/day, equipment depreciation in $/MBF, operating cost in $/MBF where total cost was the sum of the equipment depreciation and operating cost.

Since this analysis is solely for stump to truck operations, log truck drivers were not incorporated in the cost estimation. Once costs for the cable yarding settings had been determined for the dual units, a price comparison was done against the cost estimates calculated in Helipace to determine which harvest approach was more economically feasible.

Cost Verification

In order to ensure quality of results, harvest cost estimates were checked using other methods. Cable and ground harvest costs were verified using cost estimate equations found in the Feric Report, "Harvesting Coastal Second-Growth Forests: Summary of Harvesting System Performance" (1998). These equations estimate production and costing for various harvesting methods (i.e. manual falling, bucking, processing) and equipment (i.e. cable yarding, mechanical processing, skidding). Individual harvesting costs are then summed to make a harvest system.

A summary of the following cost estimates can be found in the table XXX: Feric Harvest Costs. With an average production from the Region 6 costing spreadsheet of 42 MBF/day for a central tower setting, the average cost/setting of $166/MBF is close to the anticipated cost from the Feric equations (about $168/MBF). With an average production from Region 6 costing spreadsheet of 73 MBF/day for a mobile tower setting, the average cost/setting of $112/MBF is moderately higher than the estimated cost from Feric equations (about $94/MBF).

The average production from the Region 6 costing spreadsheet for a ground based setting is 50 MBF/day with a cost of $103/MBF. This cost is moderately higher than the Feric estimate of about $87/MBF.

The Feric estimates appear to be within at least 16% of the Region 6 estimates. A closer correlation could be obtained by considering factors taken into account in the Region 6 spreadsheet. These factors include slope of the terrain, move in/out, rigging up/down, setup/breakdown time, and an accurate estimate of personnel.

Equipment Costing

Equipment costing was determined from the Region 6 cost and production analysis spreadsheet. This is the most up-to-date pricing for the more commonly used pieces of equipment. The equipment that was used for our analyses can be seen in Table 7.5: Cable and Ground Based System Pricing.

Central Tower

The Madill 172 Yarder has a 70-ft. tower and was analyzed for central landing locations, using PLANS. This yarder would be used on ridgetops and ridge noses with adequate landing spaces. This versatile slackline yarder can be rigged with either a 1 1/8-inch or 1inch skyline. The external yarding distances (EYD) would be 2000 feet and 2500 feet respectively. The carriage option was the Eagle IV carriage. The minimum size for an acceptable landing is 1 acre. In places where landing space is available, a log processor can be used and tree length logs can be yarded.

Mobile Tower

The choice for the mobile yarder was a Madill 124 Swing Yarder. The EYD is 2000 feet, using ¾ inch main, haulback, and slackpulling lines. This swing yarder is capable of decking logs and with available space it can operate on continuous landings with or without a loader. The landings can be on road grades of less then 11%. The carriage option selected was the Eagle IV carriage.

Ground Systems

The Madill-2200 hot saw model was our choice for ground based systems. The feller buncher is capable of working on side slopes up to 35%. Ground skidding will be used on slopes with less than 30 percent since soil stability and ground conditions within this range are considered acceptable. The track skidder operates effectively on slopes up to 30 percent. In addition, it operates more effectively at greater external yarding distances. For this analysis, shovel yarding was not considered because the maximum external yarding distance for shovel yarding is assumed to be 400 feet. Once the track skidders bring the turn into the landing, a log loader then loads the log trucks. For our analysis, we chose the Komatsu PC200.