Passenger travel and the shipment of goods by sea have traditionally been highly economic but slow, the limit to increased speed being imposed by the high costs of technical innovation and excessive energy consumption. At the same time, the concept of increasing the speed of ships has continued to attract the attention of shipowners because it is a key criterion for the efficiency of marine transportation, and thus for the competitive position of carriers. This has encouraged their constant interest in discovering ways to overcome the limitations, through high-performance propulsion systems and improved hull designs leading to reduced drag. Table 8.1 summarises the major technological advances in propulsion since the early nineteenth century, when the speed of the first steam-powered ships was little better than that of sail.