What Is a Tug / Tugboat?
Tugboats are relatively small compared to other ships, especially when large modern tankers, cargo, and drilling vessels are considered. They’re used to tow disabled ships, and also move barges and oil platforms to an intended location. A tug may be overshadowed by the size of the vessel it is transporting, but it can navigate it through a crowded harbor area or a narrow channel. Many are capable of salvage operations or even firefighting.
On average, a tugboat has a 680 to 3,400 horsepower engine, but they can go much higher. Larger tugs that operate in deep waters may have engines as powerful as over 27,000 horsepower. In general, marine vessels have a tonnage ratio of 0.35 to 1.20. However, a large tug may have a tonnage ratio from 2.20-4.50. Some harbor tugs have ratios of 4.0 to 9.5, demonstrating the power at which their engines can efficiently drive a propeller under a very high weight loads.
Types of Tugboats
There are several different types of tugs, each with its own advantages. The one chosen depends on the type of port and how much traffic it experiences on a regular basis. It also depends on the types of ships that use the part, what navigational obstacles are present, and local laws concerning maritime travel and environmental protection. Crew experience and the types of tug vessels available also help determine the configuration of tug to use.
- Conventional Tug: These can be seen in most ports of the world, and are the oldest types of tugboats. Although not as maneuverable as some modern designs, they can get the job done thanks to diesel engines and one or two propellers and a rudder. The towing hook is usually in the middle, and the power plant is at the stern. Downsides to using conventional vessels include slow repositioning and the location of the towing system, which can cause the boat to capsize in extreme conditions.
- Tractor Tug: In use since 1950, this vessel uses a different kind of propulsion that supports a turning axis pivot. Its multi-direction propulsion system enables the ship to turn on its axis 360 degrees. Vertical pitch blades below the hull, with rotating wings, allow the tractor tug to be positioned and steered with precision. Downsides include vulnerability of the underwater propulsion to be damaged, a side list at full speed, high investment and maintenance costs, and poor steering in open seas, but maneuverability and the ability to instantly apply full power are distinct advantages.
- Azimuth stern drive tug: Azimuth propulsion adds maneuverability. More recent models feature two stern-mounted nozzles rather than one, and some even place these amidships – “Z” type tugs have higher turning power and increased bollard pull per kilowatt of power. Demounting and maintaining the nozzles is simpler as well. However, this type of vessel has limited size and movement, is prone to mechanical damage to nozzles, can list to the side, and is sensitive to ship interactions.
Other common names in the tug industry include common harbor tugs, which often serve as towing and salvaging ships; they’re typically small and may have tires for fenders. Larger in size, anchor handling towage supply tugs often serve oil rigs and platforms and have room for equipment such as anchors and cranes.
River tugs are engineered for use on inland waters. They’re usually designed to push vessels such as barges; the typical design is a flat front. An articulated tug and barge has a front end shaped to fit into the back of a barge. These are noted for their high-set bridges. Ship docking module tugs are specifically designed to aid other vessels when they’re docking in marinas and sheltered harbors. Low and wide, these can get close to any section of a hull, and feature two 360-degree thrusters to quickly provide control from any angle and direction. They can also speed up quickly to reduce the reaction time when vessels need to be positioned in tight areas.
Given its power, a tugboat must be protected. Most of them have fender systems that allow them to come in contact with larger vessels without being damaged. These abrasion-resistant fenders are also called boat bumpers and marine fenders and come in various types. The main variations include:
- Cylindrical: Attached to the bow or stern, the fender is flexible and can withstand being pushed against flared hulls. It supports use with different ship types and is suited for the open seas. A support chain typically goes down the center of the fender, which is supported by chains and straps that are fitted into pre-formed grooves. They’re typically installed in segments around the perimeter of the tug.
- Block: Also referred to as cube boat bumpers, block fenders have a more traditional shape and contact over a larger surface area. Therefore, they exert low pressures on hulls. A balanced grooved surface allows the bumper to provide a firm grip. This type is well-suited for use in stormy weather and when there are high swells on the water surface.
- M-type: Tugs with M-Fenders on their bow and aft sections have reduced pressure while pulling and pushing. These fenders also have a groove surface for a tight grip. Also, they have triple legs that firmly attach to the vessel. Other advantages include a low weight, for stability, and a heavy-duty design.
- W-Fenders: Suitable for use in extreme operating conditions, these are quite common. They can be installed around the curves of most hulls, regardless of shape. In addition to a customizable tensile strength, the fenders withstand collisions between docks and ships. This type is often seen on large harbor tugs and those that traverse the open ocean.
The three most common jobs aboard a tugboat are captain, mate, and engineer. Safety is a major concern when working on these vessels; the International Maritime Organization issues a special training course called STCW 95, while the U.S. Coast Guard and Occupational Safety and Health Administration have implemented many safety-focused standards. When the guidelines aren’t followed, the likelihood of injuries increases and compensation due to the negligence of liable parties is available under maritime law.