Why tug boats

Barges can be used to move almost anything that a ship can, and the tugboats move them from one place to another. A tugboat's role in a construction project is more varied and complex. Typically, a tug assists in construction by moving small barges carrying the construction equipment from place to place on a construction site.

The tugboat can also act as a crew boat so that the construction crew can get around at crew change time. Whatever their tasks, tugboats are essential to the marine industry. These workhorses of the sea can move vessels hundreds, even thousands, of times their own size.

These tenacious little boats offer a perfect example of why it is always best not to judge a book by its cover, or in this case, a boat by its size. Image Credit: MarineLog. Why are tugs needed? Tugs fill a few different roles:. Tugs carry firefighting equipment to provide assistance in case of a fire. Moving barges, rigs, and other floating equipment that does not propel itself. Helping a boat through narrow areas, in inclement weather, or docking and mooring. The last role is usually the largest, but why do large ships need help getting into and out of port?

The larger ships grew, the more they could carry long distances, but the less agile they became at low speeds and in tight spaces. Moving sideways is particularly difficult for vessels that can be hundreds of meters long. Often, when huge vessels like container ships and LNG ships get close to port, they are escorted by a tugboat, ensuring they take the safest route. How do they move large ships? Depending on the size of the ship and the tugs, once in port, one or more tugs can tow via a tow line or push the ship into dock.

The tow line can be used for direct or indirect towing. With direct towing, the tug is pulling the vessel straight ahead, likely due to the ship not having the ability to propel itself. Hence one reason for having a pilot on the bridge — he can see everything, and can tell the tugs when to push, when to pull etc. So tugs are almost always responding to orders from a pilot in harbours and rivers.

Read more about Damen Shipyards in our Supplier Directory. Therefore, we are also investing heavily in this field to cope with the challenges of the future. So, along with the appropriate technology of the tugs and with the help of pilots, tugs can be vital for ensuring that vessels can make a safe transit; and with automation becoming more important for tug operations, it appears to be an up and coming trend in the development of tugs.

According to Crowley Holdings, the technology available for designing and building tugs can be vast, and it is more important to balance commercial viability with the best available technology.

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Its stern consists of the power plant complex. These tugboats are designated on the basis of a number of propellers in them as: Single screw tug implies one propeller conventional tug, Twin-screw tug implies two-propeller conventional tug and Triple screw tug implies three propeller conventional tug.

Advantages: The main advantages or features of conventional tugboats are as follows: The construction of conventional tugs is quite simple which requires less maintenance, so the maintenance and construction cost if these tugs are very low as compared two other two types of tugs.

These are self-sufficient thus requires no support system. Smaller is the propeller larger be the open water. These tugs have an upper hand and maximum efficiency in towing carried for port-to-port. These provide complete assistance with pushing and tugging operation while carrying towing on a line. The operation cost is quite low and seems economical while working with moderate-sized vessels. There may be certain disadvantages of conventional tugboats and these are briefed as follows: The designing principle is very old thus it degrades the performance standards.

They are unidirectional and cannot work in the reverse direction until provided with a reduction gear to facilitate reverse flow. There are more chances of cavitation in these tugs.

The stability and strength of these tugs is less as compared to the other two. Their usage is limited to small and medium boats due to obsolete design principles so azimuthal stern drive tugs and tractor tugs are employed to assist the mega boats. The repositioning of the tugs is quite slow due to restricted manoeuvring capacity. There are more chances of capsizing or overturning of the vessel which results in fatal accidents. To overpower this issue of capsizing and halting the development of girting, a release hook is required.

Conventional tugs have low values of astern power 2. Tractor Tug: The key to the true tractor lies in the use of 2-multidirectional propulsion unit, of which some are rather like large rotating outboard motors with other consisting of rotating vertical blades.

Advantages: It being the most important type of tugs, tractor tug has many positive points. Some of its advantages are briefed as below: These are the only tugs which provide full thrust over degrees. They have rapid power-on response time and are well known for their outstanding manoeuvrability. In contrast to the conventional tug, tractor tugs are adaptable to repositioning swiftly on the will of the pilot or on demand of the towing job in which they are employed. So these are readily available tugs with high-efficiency values.

Their control systems are very simple and they pose a very low risk of girthing or capsizing. These have an extraordinary performance with fast speed. They can effectively overcome the interaction forces when interacting with ships at some close distances. They can work efficiently in sideways movement due to the close location of the propulsion unit to the turning point. They have improved operational capability in a restricted area such as a lock flow channel.

In these types of tugs, a rudder is not required that is the use of rudder can be eliminated. They have reliable and robust propulsion units. Disadvantages: The tractor tugs are the most effective and most powerful sort of tugs. As everything has certain cons along with pros these too have certain loopholes mainly their complexity and cost and other drawbacks of these tugs are as follows: These kinds of tugs have less bollard pull as compared to ASD tugs.

They are considered to have very high capital investment costs it implies a lot of money is required to buy these tugs and maintain these tugs. In short, it confers that initial and maintenance cost of tractor tugs is very high.

The repair and maintenance of complex under-water units of these tugs are quite expensive Handling in an open seaway might be poor with the short distance between the pivot point and the thrust creating a short turning lever Heeling angle with full side thrusts may be up to 21 degrees with some tugs. Azimuthal Stern Drive ASD Tugs : These tugs are midway between conventional tugs and tractor tugs as these utilize some of the benefits of both conventional and tractor tugs.

Advantages: These are considered more efficient than conventional tugs but less efficient than tractor tugs. Major advantages of using ASD tugs are as follows: Better directional stability at speed They are more suitable hull form for open waters and working in a seaway They have improved bollard pull The azimuth units are easy to withdraw for maintenance and repair The maximum heel with side thrust is less than 15 degree which is in contrast with tractor tugs having the value of twenty-one degrees.

These tugs have a shallower average draft of 3m Disadvantages: These tugs are difficult to work with as compared to tractor tugs and other drawbacks working with these tugs are as follows: The side-stepping ability of ASD tugs is not so good. The squat at the stern and flooding of the aft deck has been acquainted with occurrence with certain types when backing with full power They are still susceptible to girting or capsizing when using aft towing position.

Tractor Tugs With Cycloidal Propellers: Before Second World War tugboats developed were of high power rating and large tonnage capacity, the propeller used were cycloidal to serve the manoeuvrability purpose; these were renowned as Cycloidal Tugboats.