Tugboat engines typically produce 500 to 2,500 kW (~ 680 to 3,400 hp), but larger boats (used in deep waters) can have power ratings up to 20,000 kW (~ 27,200 hp) and usually have an extreme power: tonnage-ratio (normal cargo and passenger ships have a P: T-ratio (in kW: GRT) 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 railroad locomotives, but typically drive the propeller mechanically instead of converting the engine output to power electric motors, as is common for diesel-electric locomotives. For safety, tugboats' engines often feature two of each critical part for redundancy.

Tugboats are highly maneuverable. Kort nozzles are added to increase thrust per kW/hp. This was followed by the nozzle-rudder, which omitted the need for a conventional rudder. The cycloidal propeller was developed prior to World War II and was occasionally used in tugs because of its maneuverability. After WWII it was also linked to safety due to the development of the Voith Water Tractor, a tugboat configuration which could not be pulled over by its tow. These propulsion systems are used on tugboats designed for tasks such as ship docking and marine construction. Conventional propeller/rudder configurations are more efficient for port-to-port towing.

The Kort nozzle is a sturdy cylindrical structure around a special propeller having minimum clearance between the propeller blades and the inner wall of the Kort nozzle. The thrust: power ratio is enhanced because the water approaches the propeller in a linear configuration and exits the nozzle the same way. The Kort nozzle is named after its inventor, but many brands exist.

A recent Dutch innovation is the Carousel Tug, winner of the Maritime Innovation Award at the Dutch Maritime Innovation Awards Gala in 2006.[6] The Carousel Tug adds a pair of interlocking rings to the body of the tug, the inner ring attached to the boat, with the outer ring attached to the towed ship by winch or towing hook. Since the towing point rotates freely, the tug is very difficult to capsize.[7]

The Voith Schneider propeller (VSP), also known as a cycloidal drive is a specialized marine propulsion system. It is highly maneuverable, being able to change the direction of its thrust almost instantaneously. It is widely used on tugs and ferries.

From a circular plate, rotating around a vertical axis, a circular array of vertical blades (in the shape of hydrofoils) protrudes out of the bottom of the ship. Each blade can rotate itself around a vertical axis. The internal gear changes the angle of attack of the blades in sync with the rotation of the plate, so that each blade can provide thrust in any direction, very similar to the collective pitch control and cyclic in a helicopter.

A tugboat is a boat which maneuvers vessels by pushing or towing them.

Mainly used for

• Vessels that should not move themselves ( Eg:Ships in crowded harbor)

• Platforms or vessels that cannot move themselves(Eg: Oil platforms, Barges)

Tugboats are strongly built for their size and some of them even assist in firefighting




Tugboats are mainly classified into 3 types

1.      Seagoing

2.      Harbor tugboats

3.      River tugboats

Seagoing:-

These are the vessels which carry the ships to the sea.These are classified according to the connectivity between the tug and thebarge. The classification is as follows

1.      Notch tug

2.      Integrated tug

3.      Articulated tug & Barge

Notch tug:-

It is tug specially designed to aparticular Barge. The tugboat contains a towing winch at its stern but the specialtyof it is that it has a deep notch at the stern (as deep as 90 ft.). The notchis built in exact shape of tug’s forward hull.  Now the stern of the Barge snugly fits into thenotch present at the stern of the tug and the combination becomes a ship. TheBarge and the tug are firmly attached with the lines. The main advantage isthat it can be moved faster than in normal towing. When the weather conditionsare extreme the lines are let loose so they get separated but it is notgenerally recommended because that will damage the tug and tow. Operating in the notch shields the tug from sea conditions and is themost advantageous position for maneuvering the tow.






Integrated tug:-

The Integrated Tugand Barge (ITB),comprises specially designed vessels that lock together in such a rigid andstrong method as to be certified as such by authorities (classificationsocieties). These units stay combined under virtually any sea conditions andthe "tugs" usually have poor sea keeping designs for navigationwithout their "barges" attached. Vessels in this category are legallyconsidered to be ships rather than tugboats and barges. Navigation lights presentshould follow as required by ships rather than that of a tug and a barge.




Articulated Tug andBarge (ATB):-

ATBs are similar to that of a notch tugs but these utilizemechanical means (pins, clamps etc) to connect to their barges. They remaincoupled all the time. ATB's generally utilize Intercon and Bludworth connectionsystems. The main advantage of ATBs is speed, safety, and cost efficiency. InATBs the tow and barge may roll simultaneously but should pitch separately.






Harbour tugs:

These are used to carry the ships into the harbour or awayfrom the harbour.  The width to lengthratio is higher compared to the seagoing tugs because they need a lower draught. These are also called as Lunch BucketBoats because they are only manned when needed and only at a minimum (captainand deckhand), thus the crew will bring their own lunch with them.






River tugs:

These are often referred to as towboats or push boats.Their hull designs would make open ocean operation dangerous. Their hullsfeature a flat front or bow to line up with the rectangular stern of the barge,often with large pushing knees. They can tow a large fleet of barges