Motor Truck Logging Methods / Engineering Experiment Station Series, Bulletin No. 12

The non-skid or caterpillar tire may well be used on heavy grades or where the traction is very poor, the general opinion being that it gives a firmer grip on the road and makes it safer to handle the truck in wet weather.

There is no standard width of tread for truck wheels. The widths usually used on the drive wheels of the logging truck and the wheels of the trailer are twelve and fourteen inches, respectively. The use of tires of smaller width on either trailer or truck cannot be recommended. The wider the tires on the trailer, the better it is both for the life of the equipment and for ease in handling the load. When the surface of the giant tires becomes worn down so that the grooves become very shallow, it is desirable to have the tires re-grooved. They will last a great deal longer if this is done and will also give better traction on the road. The groove makes the tire lobes act separately on the uneven places in the road so that only one lobe is subjected to the strain of the irregularities instead of the whole tire. This is also true with reference to the strains that are set up internally due to the twisting of the rubber.

Chain Drive. Trucks equipped with a chain drive should be supplied with an extra set of chains so that they may be changed and cleaned every week. To clean the chains, they should be soaked in kerosene which removes the dirt, grease and gum that has accumulated. By doing this the life of the chains will be quadrupled. The small amount of time that it takes will pay.

Top. The truck should come equipped with a top over the driver’s seat that is easily detachable. In bad weather the driver should be protected from the elements, but the top should be removed in good weather as it is in constant danger of being broken during loading. Many operators leave the top off entirely and the driver must dress for the weather. A good demountable top will add to the comfort of the men and often helps to keep a good man at his job.

TRAILERS

The development of the trailer has made motor truck logging practical. Every truck has greater tractive power than it can utilize in the propulsion of the ordinary load. Its limitations are due to a short-bulk carrying capacity and not to any lack of pulling power. The ordinary truck has a draw-bar pull of 2600 pounds. The draw-bar pull per ton of load varies from the minimum of 50 pounds on a level pavement to 250 pounds on a level dirt road, depending upon the character of surface.[5] Twenty pounds of additional pull are required for each degree of gradient. For example, a fore and aft plank road offers a resistance of about 60 pounds pull to a ton of load. If this were located on a seven per cent grade, it would require a 60 pound pull to overcome the load resistance plus seven times twenty or 140 pounds additional pull for the grade, a total of 200 pounds to pull one ton. Dividing 2600, the draw-bar pull of the truck, by 200, the resistance offered by road and grade, gives 13 tons as the load that can be pulled by the truck over this surface and grade. As this must include the weight of the trailer, which when equipped for logging is about three tons, it leaves a total of 10 tons that the truck can pull. This is equivalent to about 3000 feet B. M. of Douglas fir logs, the average load that is hauled. While such an adverse grade as cited in this illustration is avoided if possible with a loaded truck, the illustration will serve to show the pulling capacity of the truck. The hauling of loads of this size would be impossible without the use of the trailer. The normal load, then, may be increased two, three, or even four times, by the use of the trailer, over the maximum load that can be carried by the truck alone.

Objection to the trailer that it tends to shorten the life of the truck is hardly worth consideration. According to a careful analysis it has been estimated that the use of the trailer does not shorten the life of the truck by more than one year, which is of little consequence when the saving due to the size of the load that can be carried is taken into consideration.

Description of the Trailer: The frame of the trailer is constructed of heavy steel channel bars which support the twin bunks used for logging, and for the substructure to carry the body when used for other service. The steel frame is supported by semi-elliptic springs held by shackles similar to those of the truck. The springs rest securely upon the axle, are clamped to it by U-bolts, and are relieved from side stresses by radius rods which connect the axle to the frame.

The trailer is coupled to the truck by a reach which is passed through guides secured to the hounds of the trailer. The latter may slide upon the reach and is held in the desired position with reference to the truck by means of clamps. The hounds are located fore and aft of the axle and are connected to it by steel plates. The square reach is more favored generally by loggers than the round type for the reason that it can be more easily adjusted, particularly the round reach that is cut in the woods, which is irregular and has to be clamped very tightly in order to make it stay in place. Holes bored through the square reach makes the adjustment easy. Combination steel and wood reaches, the sides being of channel iron and the center of wood, are favored by some operators.

The twin bunks of the trailer carry the load in balance upon the axle independent of the reach, thereby relieving the reach of all vertical stress. (See illustration below). The rear bunk is just an ordinary wooden affair designed only to help support the weight of the logs. The front bunk is of the same construction as the one on the truck (described above) and serves to hold the load in place.

Brakes. All trailers should be equipped with brakes when negotiating heavy grades. A device connecting the trailer brakes to the truck permits a ready control from the driver’s seat on the truck. The brake outfit is easily attached to the truck and consists of a ratchet and lever which winds a one-quarter inch cable on a small drum. The cable winds around a second drum which is attached to the frame of the truck about six feet back of the driver’s seat. A third drum in the center of the chassis attached to the shaft of the second drum winds a cable which goes to an equalizing bar just in front of the trailer brake. As the ratchet and drum are tightened, the motion is transmitted through the second and third drums to the equalizing bar. Two arms extend from this bar to roads which when pulled forward, move a bar attached to the road in such a way that the brake band in the inside of the brake shoe is extended against the shoe, applying the brakes evenly to each wheel no matter how uneven the road-bed or how sharp the curve. A spring attached to the reach clamp pulls back the equalizing bar when the brakes are released. A heavy spring on the drum in the center of the shaft on the truck allows for curves so that an even pressure is always maintained.

A simple and it is claimed an effective air brake for motor trucks and trailers is now being marketed by an air-brake concern of San Francisco but it has not yet been tried out in the logging industry. “Braking action is secured by means of a diaphragm and pressure plate. The diaphragm is directly connected to the brake-band lever. No air compressor is used in this system. A small air receiver or storage tank takes the spent gases from one of the cylinders by utilizing the outlet afforded by a priming cock. The brakes are applied by a control system mounted on the steering column. By means of a quickly adjusted hose connection, air can be applied to the wheels of the trailer using the control which governs the braking of the truck. The air pressure in the storage tank is automatically maintained by means of an accumulator valve which closes when the tank pressure reaches 150 to 175 pounds. If the tank should be empty at the top of a long grade, sufficient pressure is generated by the compression of the engine to operate the brakes. Opening the throttle to full emergency position will apply maximum braking effect without sliding the wheels.”[6]

This system has not been tried out under the conditions as found in the woods but if it can be made to work satisfactorily it will be a big improvement over the old system as the driver will then have instantaneous control over the load at all times.

LIFE AND DEPRECIATION

COST DATA

The items of expense are here segregated in such a manner that they may be used as a basis for figuring the cost of hauling logs under average conditions. These costs are for the truck and trailer as a unit. If a road has to be built, the overhead charge of the road per thousand feet of timber hauled over it together with the cost of upkeep must be added to the figures given below in order to know the total cost of transportation per thousand feet.

3000 FOOT CAPACITY, OUTFIT COMPLETE

The following figures are for a 31⁄2-ton logging truck with a 5-ton trailer. The figures are based upon a 275 working day year.

RUNNING EXPENSES PER MILE

FIXED CHARGES PER 275 WORKING DAY YEAR

TOTAL EXPENSES

FIXED CHARGES PER 275 DAY YEAR

TOTAL EXPENSES

The above costs will be found to be approximately correct for average operations. They will vary somewhat with the road conditions, loads, grades, and the efficiency of the driver. These variations, however, will be slight. They will not amount to more than one cent per thousand feet per mile of haul. The investment pays the owner six per cent and provides renewals for all time. The interest charge is based on the total cost of the equipment less the cost of the tires. The tire cost is deducted in figuring the interest charges because this item is covered under running expenses. The resale value of the truck at the end of four years is not deducted from the interest charge, because this sum is tied up for that length of time. Renewal for the equipment is taken care of by the creation of a sinking fund based on an average life of four years. Theoretically, on a 5-ton truck, $1157.13 is put aside each year for four years at the expiration of which time the aggregate of these savings together with the resale value of $1900, automatically provides for the purchase of new equipment.[7]

A fifty-mile haul may be used as an illustration for figuring the total running expense of the 5-ton truck. This means that the truck makes trips enough to total fifty miles for the day’s run. The cost per mile, including gasoline, oil and repairs is 26.4 cents. It will, therefore, cost $13.20 for the fifty miles. To this amount must be added $12.92, daily overhead charge, making a total of $26.12 for fifty miles traveled or 52.2 cents a mile. With an average load of four thousand feet the cost will be 13.0 cents per mile per thousand feet. A glance at the table will show that the greater the mileage and the larger the load, the less will be the overhead expense and consequently the cost per mile per thousand feet. To these items must be added the cost and maintenance of the road if one has to be built.

ROAD CONSTRUCTION

There have been some very successful operators who have secured a small body of timber at a low price on a public road who made the motor truck pay without building a road. This method of logging in a small way will continue to be carried on by small operators who will haul only during three seasons of the year or even less. However, the big future for the motor truck for logging is in the larger tracts of timber where it would not pay to put in a railroad but where a good type of motor truck road can be built cheaply and loads as large as the truck can handle be carried with no road restrictions as to the weight.

In general four types of roads are used by loggers: (1) the cross-plank road, (2) the fore and aft pole road, (3) the fore and aft plank road, and (4) the cement road. The puncheon road is a modification of the fore and aft plank road and will be taken up with the latter. The methods and cost of construction, the advantages and the disadvantages of these various types of roads follow in detail.

Sub-Grade: The sub-grade is put in the same way for each type of road. The average width of the truck is seven feet and six inches, calling for a road about eight and a half feet wide, so that the sub-grade should be twelve feet in width. An illustration of the amount of grading necessary is shown on page 25. Too much care cannot be taken in the matter of ditches for draining. In a rainy climate, the water should be carried away from the hill side of the grade every fifty feet.

Cross-Plank Road: The cross-plank road is constructed by laying cull ties on hewn poles lengthwise of the road. Three rows, four feet apart are used and second grade ten foot plank, six inches thick and of random widths, are securely nailed to the ties. Great care must be taken to have the ties laid fairly smooth if the road is to be even. Plank less than six inches in thickness should not be used as the thinner ones very soon crack and go to piece under the excessive jar and vibration.

This is a very expensive road to build as it wastes material. Six thousand feet of lumber is necessary for every hundred foot station, at a cost of $222 a station for the material alone, without considering the cost of laying it. The maintenance cost also is very heavy because the nails pull out as a result of the vibration caused by the truck. This type of road is used only over short stretches, such as swampy ground in connection with the dirt road, and on steep grades and sharp turns in connection with the pole or plank road.

The Esary Logging Company at Camano Island, Washington, put in a cross-plank road for a short distance on a sharp curve and a steep grade, to see how it would affect the traction. It was found that cross planking was not necessary on curves where the grade is ten per cent or less when coming down with a load, providing trailer brakes are used. In the future the company will not use this type of road unless grades above this maximum are encountered. It is impossible to lay a cross-plank road smoothly because the stringers settle and make the road bumpy. The resulting jar on the equipment and the fact that these stretches have to be taken at a much reduced speed, furnish ample reason to condemn its use.

The only real use for a cross-plank road is to secure better traction on grades exceeding ten or twelve per cent, and then it should be laid with a space of about one inch between the planks. Even in such cases it would be better to use some other method for securing traction, such as sanding the track or winding the drive wheels with a light cable. The waste of material and the excessive vibration limit the use of this type of road.

Fore and Aft Pole Road. In the fore and aft pole road, poles from twelve to fourteen inches in diameter are hewn on one or more faces and laid longitudinally with the road, with one or more logs for each wheel track. This type of road is commonly used by motor truck loggers and is one that lends itself readily to their use. It is the most practical road that can be built unless there is a small saw-mill handy to saw planks for the fore and aft plank road. The smaller material growing along the right of way is used at an expense of only what it costs to fell it, hew it and put the poles in place. Hemlock poles may be used to advantage.

Some operators use the single large pole placed on cross-ties eight or ten feet apart and use lighter eight-inch poles placed on the outside for a guard rail to keep the truck from leaving the track. The main pole is laid in a ditch about eight inches deep, leaving it half buried. This helps to keep the poles from spreading and increases their firmness and strength. The pole is notched into the cross-ties, which are made of logs not less than eight inches in diameter, and is securely nailed or bolted to prevent it from rolling. The outside guard rail is laid on the surface of the ground close to the main track and is securely braced from the outside by means of posts sunk into the ground or it may be spiked to the main pole or to the ties. When running with the trailer on this narrow type of road, the guard rail is very necessary.

After the poles have been laid, the sub-grade should be ditched in the center deep enough to carry away the water that falls in the middle of the road. The success of the road depends to a large extent upon good drainage.

The Meicklejohn and Brown Logging Company near Monroe, Washington, operate over a pole road with three poles for each wheel. The poles are from ten to twelve inches in diameter at the small end and are hewn to a six inch face, giving an eighteen inch bearing surface for each wheel. (See illustration on page 29.) The minimum sized pole that should be used for roads of this character is one eight inches in diameter at the small end. The road is constructed the same way as the single pole road and the poles are laid on cross ties twelve inches in diameter placed from eight to ten feet apart. Where the road is off the ground as when crossing over a small depression, these sleepers must not be over five feet apart. The guard rails at this operation are held in place by means of a wooden brace nailed from each end of the rail to a near-by stump. The ends of the poles used for the track are adzed so that they match evenly. By breaking the joints and hewing them the road presents a level surface with no bumps.

In planning the curves, it is necessary to make the tracks somewhat wider than on straight stretches in order to keep the trailer from running off. The track should be three feet wide on sharp curves and provided with a stout guard rail if there is any danger of the truck leaving the track. The curves are banked on the opposite side from that used on railroad curves. That is, the inner rail is raised about three inches. This is to throw the load to the outside away from the inner guard rail, making it easier to make the turn without the rear wheels binding. In this way a 35 degree curve may be negotiated with forty or fifty foot logs. As the curves have to be passed at a much reduced speed, there is little danger of the logs rolling off due to the raised inner rail.

The grading for a road of this construction is usually light. The grades should, if possible, be kept below five per cent. A truck will operate better on a ten per cent grade in dry weather than on a five per cent one in wet weather. On a road of this type, grades up to ten per cent can be operated over unless there is snow. When the grades are above this and the weather is wet, traction still may be secured by sanding the road or by tacking an old half inch steel cable to the road in the form of a figure “s”. If this is sanded in addition, the truck may safely be taken up a steeper grade than it would be safe to bring it down without sanding.

The pole road could be greatly improved by hewing the faces of the poles where they come together side by side so that an even fit is made. The details of this improved form of construction are shown in figure 1, page 30.

The cost of a fore and aft pole road varies with the accessibility of the material and the cost of the labor. In the past they have been built for as low as $2000 a mile, but with the present prices costs will range from $5000 to $7000 a mile. One company within the year contracted the grading and construction of the road for $70 a hundred foot station, not including the cost of clearing and chunking out the right of way. The total cost was about $125 a station or $6600 a mile.

Some of the advantages of the pole road are that it is tough and strong and does not crack, split or break easily so that if it is properly put in it lasts and requires but little maintenance. The material for its construction is found along the right of way and being small in diameter is less expensive than other road materials.

Fore and Aft Plank Roads. This type of road is constructed by placing cross-ties from eight to ten feet apart, center to center, upon which are placed lengthwise for each wheel, two or three sawed timbers not less than six inches in thickness and from twelve to fifteen inches in width. A good road of this type will deliver 150 million feet of logs at a conservative estimate.

The grading is usually light and in many places entirely unnecessary. Second-grade six by eight ties with the eight inch face placed down, or hewn poles are laid about eight feet apart. Where the road bed is soft, the ties are placed closer and in some places as near as two and a half feet apart. Over very swampy ground, the road known as the fore and aft puncheon road is used. It consists simply of cedar puncheon placed crosswise of the road with the usual planking nailed securely to it. The plank used should never be less than six inches in thickness in the main road as it has been proved that four inch plank very soon give way under the heavy loads. On the spur lines it is practicable to use four inch plank because the road is used only a short time.

The total width of the road is eight feet and the plank are laid on top of the ground, but if they are sunk nearly to the level of the ground the road is made considerably more firm and enduring, and of course is safer. The ends are adzed smooth to present an even surface, drift-bolted to the ties, and all joints broken.

The plank in the track are kept together by means of a three by four inch timber driven tightly between the tracks on top of the cross-ties at each joint, and a block nailed to the outside of the tie at each joint with a wedge-shaped piece of wood driven between it and the plank. (See illustration on page 33.) This wedge is driven in from time to time as occasion may demand. If, in addition to this construction, dirt or gravel is filled in the center to the level of the track, the road is made very solid.

With a good road of this type and a bearing surface of thirty inches, the trouble and expense of a guard rail may be eliminated. When a light truck is used for a small body of timber such a wide and heavily constructed road is not practical. In this case, a four inch plank with a fifteen inch surface and an eight inch pole for a guard rail would be used. Here again the track must be made wider on the sharp curves, often as wide as three and a half feet. Usually, the inner rail is made wider than the outer one. On very sharp curves the track may have to be planked solid to keep the trailer from running off. By sawing out chips from one-half to one inch wide two-thirds of the way through the plank, and about six feet apart on the inner side, a long plank may be bent around quite a sharp curve. The ties, of course, should be placed so as to allow the cut sections of the plank to rest squarely on them. This does away with the short pieces and so strengthens the track.

The company logging at Camano Island, Washington, operates over a road of this type, an illustration of which is shown on page 38. The difficulties encountered in the construction of this particular road were very considerable as a cut through very hard shale, in some places as much as seven feet, was necessary. The maintenance on this road is heavier than is usual. Two men are employed to work on it continually. The work consists of blocking up the loose ties and plank, making any necessary repairs and keeping sand and gravel on the steep grades. The cost of this work is good insurance as it keeps the road in the best of condition at all times and saves on other operating expenses.

Cost. The first cost of a road of this type is high but it more than pays in the long run if a large body of timber is to be hauled over it. The timber used in its construction amounts to about 160 thousand feet per mile. Second grade material can be used at a cost of approximately $5,500 a mile for the plank. The total cost per mile varies from $6,000 to $8,000. The plank road at Camano Island cost $20,000 for two and three-quarter miles, which includes the cost of the plank, the grading and labor of putting the plank in place. This is at the rate of about $7,275 a mile, or approximately $138 a hundred foot station. The overhead charge for the road at this operation is $.75 a thousand feet of timber hauled over it. Plank roads of lighter construction have been built for $4,000 a mile. The length of life is about the same as that of a pole road, three to four years.

The fore and aft plank road is one of the best roads that can be put in where the timber is of sufficient quantity to justify the expense. The big advantage is the speed that can be made and the saving in the equipment. Such a road is very free from bumps and the jar and vibration on the truck is no greater than on a city pavement. The depreciation on a truck depends to a great extent upon the road operated over. With the above type, depreciation on the truck will not be less than five years. In addition, tire mileage will be double that obtained over a pole road, and the gasoline and repair expense will be very materially cut. Owing to the very small vibration, a load of logs can be brought to the landing as fast as it is safe to let the truck glide on a down grade. Speeds as high as 20 miles an hour can easily be taken without excessive vibration. The traction is greater on this type of road than it is on the pole road, due to the greater bearing surface. Traction on grades up to 12% is easily secured by sanding the plank.

Concrete Roads. Concrete has been suggested as an ideal road material. However, up to the present time, loggers have not been very enthusiastic about this type of road on account of the cost of construction, which is somewhat more expensive than the other types of roads, and on account of the permanence of the finished road which is beyond that needed. To the writer’s knowledge, there is no company operating in the Northwest over a concrete road of their own building. In the future such roads may be used to a limited extent on the main haul by companies which have operations extending over at least a five year period. The spur roads will probably always be of some other material.

In building such roads two tracks of concrete, one for each wheel are provided. The sub-grade should be well ditched in the center with cross ditches every fifty feet, as is done with the pole road. It has been suggested that the ditches holding the track be six inches deep and twenty-six inches wide. They are filled to the top with concrete and built with a lip four inches high and four inches wide along the outside on top of the main surface to serve as a guard rail. No forms are necessary except for the guard lip.

A word of caution here may not be amiss. Concrete roads of this nature must be regarded as only experimental, for no specific data are available for determining the proper section of concrete to be used for carrying heavy loads on so narrow a bearing surface. It is evident that the carrying capacity of such strips of concrete would be greatly affected by the character of the sub-base. It will therefore be impossible to specify a standard that can be used under all conditions.

The use of the concrete guard rail is one of the disadvantages of this road. The edges of the rail cannot be made rounding except by special forms and the rubbing of the tires against this rough surface would greatly reduce the tire mileage. In addition, the rail is so exposed to weather and hard wear that it cannot be relied upon to serve effectively for any great length of time. The placing of forms is also a considerable item of expense in building such a road. A method which would eliminate such an expense and at the same time provide a more practical rail would be an advantage.