Although Africa is more than twice the size of Europe, the European coastline is longer than the African coastline. It is longer because of its twists and turns, creating more harbours where ships can dock, sheltered from the rough open seas.

It is not economically viable to ship a product with a poor value to volume ratio in areas with discontinuous river flow. Only cargoes with a high value in a small physical size make economic sense. The reason is that the items will need to be unloaded and reloaded along the journey.

Large cargoes of bulky, cheap items such as wood, wheat, or coal are only worth transporting through hundreds of miles of continuously flowing rivers.