Tugs are vessels that have a powerful propulsion system and are used for towing and pushing other vessels or large floatable objects. Generally familiar from the port sector as assistants tug, they increasingly tend to be used in the offshore market for towing and positioning pontoons, oil rigs and installation vessels. Furthermore, tugs are deployed for salvaging and dredging works. Basically, distinctions are made between tugboats equipped with a conventionally structured propulsion system (engine, gears, shaft-drive, propeller, rudder) and tugboats with a propeller capable of rotation in any direction (azipods or Voith Schneider drives). The power of a tugboat varies according to type. An essential measure is known as bollard pull, which is measured in tonnes. Starting from a tugboat that provides port assistance and has a bollard pull of 30 tonnes, the range spans to include large offshore units with bollard pull capacities of up to 250 tonnes and more.