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Tug, as the meaning suggest is to pull something hard. Tugboats are used for the same reason, to pull ships or all sea going structures that cannot move on their own. Tugboats are strong and powerful, completely opposite to their appearance and size. A wide range of application includes towing or pulling vessels in narrow channels, rescuing in case of break down or grounding, pulling structures without propulsion systems etc. We will learn about tugboat applications in details, later in the article. Tugboats acquire the power either by steam engine or diesel engine. The size of a tugboat varies according to the amount of power required. Hence we see that a tugboat is not exactly one of the types of sailing ships but a smaller vessel used to tug ships
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Types of Tugboats
Tugboats are mainly divided according to their application and utility. The three main categories in which the tugboats can be divided are:
- Seagoing tugs
- Escort tugs
- Harbor tugs
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All the tugs pulls or tows a vessel with the help of towing lines. The main characteristic of all the tugs, including seagoing tugs is that they have low aft decks. This is to ensure that the towing lines have high freedom of movement. The point at which the towing lines are attached to tugboat must be located at the center or midship so that the forces have no influence on the manoeuvrability of the boat. The towing winches and the towing lines should be absolutely strong and sturdy as they transfer the total force of the propeller to the lines for pulling a vessel.
- Seagoing tugs have a wide range of applications as they are not constrained by any port duties. Seagoing tugs perform the following tasks:
- Salvaging or towing a vessel in case of breakdown, grounding or collision. The vessel can be miles away from the shore. Seagoing tugs are manufactured to stay away at the sea for a longer duration of time and yet retain power to pull a vessel that is much larger in size than its own.
- Used by environmentalist and researchers for surveying a particular area.
- For pulling offshore drilling platforms and also for handling anchors in the offshore industry.
- Used extensively in pulling structures that needs to be relocated. For e.g. Partly completed ships that has to be shifted from one port to another, pulling and erecting drilling rigs, moving ship wrecks away from the waterways etc.
- Used for averting a major disaster in case a ship has developed a crack in the cargo hold or an accidental leakage. These tugboats are never used for transporting purposes.
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This type of tugboats are used to escort huge vessels along narrow or dangerous passages. This facilities are provided only to massive ships whose own propulsion system is not capable of doing manoeuveribility in dangeorus waters. This facility has been introduces as a result of series of accidents in the past that had lead adverse effects on both marine and human life.
Escort tugs are small and sturdy vessels that generally operate in the confined water. They have high maneuverability power and often have azimuthing thrusters.
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Harbor tugs are multiple-utility boats that are used in ports and inland water ways for assisting and towing vessels in and out of the ports. They are also used for pulling barges used for carrying goods in inland water ways or along the ports. Harbor tugs assist seagoing tugs when the later are pulling a very heavy objects. The harbor tugs have the highest maneuverability as they have to pull and tow huge ships within small area.
Apart from that, harbor tugs are used in fire fighting and keeping ports free from ice in winter season. They have a capacity to generate a towing force at zero velocity. They are also equipped with fire fighting arrangements and equipments for fighting marine pollution.
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Ship Knowledge - A modern encyclopedia by K Van Dokkum
Jane's Ocean Technology 1979-80 / Jane's Yearbooks, 1979
On Tugboats: Stories of Work and Life Aboard / Virginia Thorndike - Down East Books, 2004