The steam ship had one big advantage over the sailing ship. Independent of wind and tide, it could make many more voyages in a given period. However, to exploit this advantage for low value cargoes such as coal or iron ore, the steamer had to become much more efficient.

To improve the efficiency of the steam engine, engineers had to ensure that the steam used had the maximum expansive power. This was a matter of making it as hot and compressed as possible when it entered the cylinder, and as cool and fully expanded as possible when it left. This proved much more difficult than it sounds. The design and construction of boilers had to advance so that they could produce steam that was very hot and under great pressure. When the pressure of the steam from a boiler increased, it was not efficient to expand it in just one cylinder. Two, three and eventually four stages of expansion were eventually needed. To reduce the temperature after the steam left the cylinder it had to be turned back to water in a condenser which was cooled by sea water. A vacuum pump was used to ensure the exhaust steam was below atmospheric pressure.

Not surprisingly, all the improvements in the design and construction of the steam engine took many years to perfect – most of the nineteenth century, in fact. The result was a highly efficient means of propulsion. It is estimated that a marine steam engine could move one ton of cargo for a distance of one mile on the amount of energy generated by burning a single sheet of writing paper! With the efficient steam engine, and also reductions in the cost of building hulls in iron and later steel, steam became a more economic proposition than sail during the final quarter of the 19th century. A steamer could make many more voyages in a given period. It could more or less guarantee delivery times. As a result, the total tonnage of steam ships in the British Merchant Navy overtook that of sailing ships during the 1880s. Sailing ships were slowly driven from most trades and, by the outbreak of the First World War in 1914, steam had triumphed. It was a short-lived victory however, because a rival to steam was already at sea, the oil engine.