Liner shipping-trades Traditionally, liner services operate between ports in an individual trade, that is, between ports of loading in a particular country or a particular coastline or ports within a range, and similarly defined ports of discharging. This is sometimes called a pendulum service. A route used by a pendulum service is a pendulum route. In cases where the ships load or discharge at more than one port, the distance is generally not great between the first and last port of loading (and between the first and last port of discharging) in relation to the ocean crossing. More and more, especially in container trades, ports are divided into main ports, outports and feeder ports. Main ports are ports called at regularly; these have a wide range of facilities and can often accommodate a large number of ships. Often they become main ports because of their geographical position combined with a good inland transport infrastructure which makes them suitable for cargoes coming from, or going to, a number of inland points. The increase in size of ships in recent years has also limited the number of ports which can be served, often a question of draught. Outports are ports served infrequently or by transhipment.These ports tend not to have sufficient cargo to warrant a regular call. Feeder ports are ports which have regular cargoes but these may be insufficient to warrant a call by an expensive deep sea vessel because of an insufficient depth of water or length of berth or inadequate cranage. These are now generally known as hub and spoke services, where the main port is the hub and the feeder ports are the spokes. In this case, the shipping line will provide a feeder ship, often simply called a feeder, normally a smaller ship which takes cargo to and from the nearest main port.Where a ship is only prepared to call at a port when there is a minimum amount of cargo to load or discharge, the shipping line will designate it an inducement port.