Tugs are in effect marine tractors. Their purpose is to push/tow vessels when they cannot use their own engines or do not have any form of self propulsion. They are designed according to the environment in which they will operate, ie harbours, rivers or deep sea and according to their purpose, ie berthing/unberthing of ships, towing barges and other floating structures, deep sea salvage operations, etc. Whilst they may be relatively small, they are very powerful for their size. Whilst the deep sea salvage tugs usually have conventional propulsion systems, harbour tugs are mostly fitted with Voight-Schneider type propulsion systems. The latter greatly enhances their manoeuvrability in confined spaces whilst the former is aimed at long distance towing.
- Tugs usually have very small freeboards.
- They are specially strengthened for pushing and pulling.
- They have very powerful propulsion systems.
- The harbour tugs have very shallow draughts whilst the deep sea salvage tugs have larger draughts.
- They have special towing points with quick release facilities.
- The salvage tugs have powerful winches and carry heavy steel hawsers.
- The bridges of modern tugs are so designed to give the operators/tug master good all-round visibility.
- The sides of tugs are well fendered.
- Most tugs are also equipped with special fire fighting appliances to assist vessels on fire.