The development of the steam engine made possible a wide variety of new ship types. This was especially so for the small craft employed in harbours, to assist larger ships, make ports more accessible, to maintain navigational aids and to provide pilots for safe navigation in port.
One of the first successful applications of the steam engine was in the tug. These powerful, manoeuvrable craft were first used to tow sailing ships into and out of harbour during unfavourable winds. This trade soon expanded, and powerful tugs went ‘seeking’ way off the coast, looking for homeward-bound sailing ships to tow into port.
When steam ships became more widespread, the roles of tugs altered. Their most important function was now to assist large ships through difficult channels and into ports, helping them to berth safely. The salvage tug also evolved as a powerful, ocean-going craft with sophisticated equipment that could assist in saving a ship which had sunk or gone aground. Such tugs are often stationed at key points near major shipping routes, both to help ships in distress and to try to prevent incidents that could result in major pollution.
Large ocean-going tugs undertake long-distance tows, for instance, relocating a floating dock, towing an old ship to the breakers or taking a new hull from its building berth to another yard to be completed. Powerful tugs are particularly important to the oil industry, to tow large structures such as drilling rigs and production platforms into position in offshore oil fields.