Maritime shipping lines try to offer the most direct services possible, but the routing this entails must be reconciled with the location of ports. The maritime deviation is the additional distance away from the main shipping routes it takes to service a specific port. The higher the deviation, the more reluctant maritime shipping companies will be to use this port along their major routes, unless the port has a significant hinterland and its associated cargo base. Ports under 100 nautical miles from a main maritime shipping route are considered to be of low deviation.
On the above figure, five ports (1 to 5) each have a deviation from the main maritime route (labeled D1 to D5). The deviation is illustrated as the most direct shipping route to the main maritime route. Port number 3 is having the least deviation and could thus be a suitable location for a transshipment hub servicing other ports with high deviation through feeder routes. From a maritime deviation standpoint, port number 5 would be the least suitable to be serviced as a port of call along a deep-sea service.
Yet, it is also possible for maritime shipping lines to deviate their own routes in order to minimize the summation of port deviations. In the above figure, an alternate route can be used and results in a reduction of the total deviation. While for ports number 3 and 5, the deviation would not change noticeably, it would improve markedly for ports 2 and 4. Thus, depending on port size and the configuration of maritime shipping routes, shipping lines will either opt for the direct or the deviated route. Those wishing to offer fast and high-frequency services will opt for limited deviations and possibly the usage of offshore hubs along the routes. Those opting for market coverage (at the expense of frequency and speed) will have more deviations. Maritime deviation remains a balancing act between the frequency of service, the number of allocated ships, and market coverage. The configuration of transshipment hubs along the Mediterranean is a relevant example of this balancing act.