30.Tug boat

A tugboat, or tug, is a boat used to maneuver, primarily by towing or pushing, other ships in harbors, over the open sea or through rivers and canals. Tugboats are also used to tow barges, disabled ships, or other equipment like oil platform.Tugboats are quite strong for their size. Early tugboats had steam eingines ; today diesel engines are used. Tugboat engines typically produce 500 to 2,500 kw 680 to 3,400hp, but larger boats (used in deep waters) can have power ratings up to 20,000 kW (~ 27,200 hp) and usually have an extreme pwer tonnage -ratio (normalcargo and passenger ships have a P:T-ratio (in kWgrt) of 0.35 to 1.20, whereas large tugs typically are 2.20 to 4.50 and small harbour-tugs 4.0 to 9.5). The engines are often the same as those used in railroadlocomotive, but typically drive the propellor mechanically instead of converting the engine output to power electric motors, as is common for railroad engines. For safety, tugboats' engines often feature two of each critical part for redundancy.^]

A tugboat's power is typically stated by its engine's horsepower and its overall .Tugboats are highly maneuverable, and various propulsion systems have been developed to increase maneuverability and increase safety. The earliest tugs were fitted with paddle wheels, but these were soon replaced by propeller-driven tugs. Kort nozzleshave been added to increase thrust per kW/hp. This was followed by the nozzle-rudder, which omitted the need for a conventional rudder. A new type of tugboat has been invented in the holland. The so-called carousel tug consists of a design wherein the flexibility and effectiveness of the tugboat's maneuvers is determined not by the propulsion system, but by a steel construction on deck, consisting of two steel rings. The inner ring is fixed to the ship, and the second ring rotates freely and carries a hook orwinch. The ship can therefore maneuver freely and independently of the towed ship, and since the towing point rotates towards the point nearest to the towed ship, the tug can capsize only with difficulty. One prototype exists presently, but the first new tugs are expected to sail in spring 2007.