Tugboat refers to the ship used to tow barges and ships. Tugboat is characterized by firm structure, good stability, small hull, large main engine power, large traction and good handling performance, but it has no loading and unloading capacity. It mainly carries barges carrying materials and various operation ships. Tugboat can be divided into ocean tugboat, inland tugboat, coastal tugboat, harbor tugboat, marine rescue tugboat, etc. according to different areas of use.
Tugboat's draft is as close to the channel water depth as possible. The bottom recess of the ship fitted with propeller is often tunnel shaped, so that the propeller diameter is greater than the ship's draft. When the propeller works, the water fills the concave part, so that the propeller is fully immersed in the water, so as to give full play to the power of the main engine and improve the propulsion efficiency. If the water depth of the channel is less than 0.6m, tandem propellers or water jet propulsion should be used.
The towing equipment of tugboat is generally towing hook. The engine power of large ocean tugs can reach more than 20000 horsepower and the displacement is more than 5000 tons. It can be used for maritime rescue, towing giant ships and other large water structures, such as offshore platforms and floating docks.