|Sorry no expansion on the next photos|
However, it is possible to configure a 4 wheel trailer to haul logs as well. Usually such a trailer is used to haul shorter lengths with one load on the truck and a second on the trailer, but long logs can be hauled as shown here as a 'bridge load'. A "bridge Load" is simply a load which 'bridges from the truck to the trailer, with one end resting on each.
The conventional log trailer shown above is steered because the logs forming the bridge effectively make up the body of the trailer. There is a steel tube running from a pintal to the trailer which is called the 'reach'. The supporting bunks on both the truck and the trailer swivel, and the reach is designed to that it will change length as needed during a turn. The pintal hight is located several feet behind the wheels of the truck, so as the truck turns one way, the pintal moves the other way. In effect if the truck steers left, the trailer is therefore steered right. This compensates for the habit of trailers to cut corners. Although it is usually not done, it is possible to configure a log trailer to follow exactly in the tracks of the rear truck wheels, regardless of how short the turn is.
The three frames which follow so a similar arrangement with a 4 wheel trailer. In these photos the truck is steering sharply to the left, but you can see how the front of the trailer has been swung to the right. It looks a little strange, but the front trailer wheels are tracking where the rear truck wheels went. This greatly reduces the corner cutting problems which are characteristic of a classic 'semi'. Western logging roads tend to be narrow and crooked, and this ability to get the trailer wheels to stay behind the truck wheels is very important on short corners.
A trailer used this way is very rare, but the system works quite well. The classic tandem axle trailer is more convenient to use and dominates the market, however the 4 wheel trailer has an advantage in hauling capacity. This is because under the weight rules widely used in the United States, a set of tandem axles is limited to 34,000 lbs while individual axles (more than 10 feet apart) can haul 20,000 lbs each. The trailer because of the frame weighs a couple of thousand pounds more than the classic trailer, but can haul 6,000 lbs more. This is not a trivial increase in productivity. The downside of the combination is that in order to get the wheelbase to use the weight, the logs need to be longer than standard 40 foot logs, so the usefulness of the combination is limited to poles or other specialty loads of extra long logs.
For many more photos showing trailer usage see here
|Alpine Log trailer|
|Set it on the truck|
|Go to Mill and wait|
|Unwrap the load|
|Up and Away|
|Load your trailer|
|Back to the woods|
What follows is a photo of a traditional western long log trailer seeing minor repairs before it gets loaded. The bunks pivot on both the truck and the trailer and the logs sit on each bunk forming a 'bridge load. A trailer like this is sometimes called a 'pole trailer' or in Australia a 'sliding pole trailer'. It is unclear to this writer whether the reference to the 'pole' is that they are sometimes used to haul poles, or because before the advent of steel reaches they often had a wooden pole for the 'reach' or tongue. The reach, of course, is not actually a tongue when the truck is loaded. The trailer is actually pulled along by the logs, and the reach has a telescope in it because it changes length as you turn. What the reach really does is steer the trailer. Notice that the truck has a lot of 'rear overhang' from the drive axles. This rear overhang swings the back of the truck (and thus the front of the trailer) the opposite way from the way you steer. This effectively steers the trailer so it follows behind the truck instead of cutting corners like a semi-truck does. Log trucks often operate on crooked, steep, narrow roads, and the fact that the trailer tracks closely behind the truck is a really good thing. The length of the reach can also be adjusted to suit the length of the logs. Typically the trailer reach is kept as long as possible (and still haul the logs) because of highway weight formulas that allow more weight if the axles are further apart.
The photographic sequence on the right shows the load and haul and unload sequence. The logs are usually loaded one at a time, and generally unloaded with some sort of a forklift.