A tug or more commonly a tugboat is a secondary boat which helps in mooring or berthing operation of a ship by either towing or pushing a vessel towards the port. A tug is a special class of boat without which mega-ships cannot get into a port. Along with the primary purpose of towing the vessel towards the harbour, tug boats can be engaged in the purpose of providing essentials such as water, air, etc. to the vessel.
A collection of tug boat related images, mostly from the interwebs. My own images are labeled "image by author" and are free to copy for non-commercial uses. All other images copyright their respective owners.