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On of the more innovative cable logging systems is known as the North Bend System. It is a suitable rigging system for a swinging , but can also be used for logging as well. By anchoring the haulback line laterally to the skyline, the butt rigging can be pulled all over the place. The skyline is raised and stays in place. Consequently, though 3 lines are required, it can be rigged with a 2 drum machine, as the skyline can be raised and tied off, or anchored with a second machine. Practical working distance with this rigging method is 1400 feet when suitable deflection can be obtained. It may be used on uphill, level or moderate downhill slopes. The load is divided between the skyline and the main line. Ordinarily, logs drag along the ground, but can be raised by hold the haulback line tight when an obstacle must be cleared.
There are other ways to rig this sort of a logging system, and my sources are not in full agreement as to what names should be applied. With the North Bend system, the yarding line goes out to the butt rigging and through a block on the butt rigging, (called a fall block because it can go up and down or 'fall on you'). From there the yarding line goes up to the carriage where it is anchored. The modified North Bend, or South Bend system as some people call it, will hang a block on the bottom of the carriage and run the yarding line through this block and double it back down to the fall block on the butt rigging. This gives you a block purchase on the skyline and provides extra lift, but at the same time, compounds the stresses on the skyline increasing the opportunity for breaking the skyline and thereby collapsing the system. The problem here is that you provide strength in the skyline by increasing deflection, and compromise the skyline strength by reducing deflection, and of course, the reason you might need extra lift is always related to inadequate ground clearances which implies that you are already compromising the deflection allowances. Consequently on the tough road one is tempted minimize the deflection, and then compound the stress with a block purchase and that is a great way to break rigging.
The alternate modification for the North Bend system is to run the yarding line out to the carriage, through a block on the carriage, down to the fall block on the butt rigging and back up to dead end on the carriage. The haulback remains on the butt rigging. You get the same block purchase as you do with the rigging other side up. The difference is that the behavior is different in the context of side yarding. In one instance the yarding line pulls straight from the logs and in the other it pulls from the carriage.