Everything You Need to Know About Tugboats

Ever wanted to find out more about tugboats? You’ve come to the right blog post! Tugs are small, powerful vessels that perform a number of tasks - specifically the towing or pushing of much bigger ships, including cargo and container ships, bulk carriers, chemical tankers and even cruise ships. The point of this is to assist in mooring or berthing operations by helping to maneuver the larger vessel into and out of a port.

One of a series of articles about different types of vessels, this post aims to tell you everything you ever wanted to know about tugboats - and possibly even some things you didn’t!

Everything you need to know about tugboats

First of all, let’s take a quick look at the history of tug boats.

The first tugboat was named the Charlotte Dundas and she was used to assist vessels on Scotland’s Forth and Clyde Canal. The patent for the tug was created by, the appropriately named, Jonathan Hulls in 1736 in England. The boat was powered by a paddle wheel and a Newcomen steam engine.

It wasn’t until approximately 1850 that screw propulsion for tugs was introduced in the USA with diesel engines following some 50 years later.

What are a tugboat’s uses?

Classed as a secondary or offshore vessel, as well as helping their larger counterparts dock and undock, tugboats are also used to provide essential supplies to bigger ships - for example water.

Tugboats can also be employed as rescue or salvage boats and icebreaker ships and some may be equipped with fire fighting equipment so that they can act as a fireboat and deployed to assist in emergencies.

Tugs can also be used to propel or pull vessels that are unable to move under their own power, such as disabled vessels - a ship that is found to be unseaworthy, unsafe or inefficient - as well as barges and even oil rigs or platforms.

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How do tugboats work?

The secret to the little tugboat’s mighty strength is their propulsion system and engines which give them their thrust. The average tug is equipped with a 680 to 3400 horsepower engine. If kilowatts are more your things, that’s equivalent to 500 to 2500 kW.

However, there are bigger tugboats which are used in deeper waters and out at sea that have engines that can reach almost 27,200 hp, or 20,000 kW.

Unlike bigger commercial vessels, a tug’s engine drives the propeller as opposed to converting the output to an electric motor supply. Tugs have two towing locations as well as two rotating azimuth units for propulsion.

As to why tugboats push instead of pull ships, this is purely down to physics: pushing rather than pulling is easier and consumes less energy when you factor in the engine power and the water resistance. Spending on the type of tug, they will push or pull the vessel either through direct contact or using a towline.

Tugboats also have a proportionally lower draft than larger vessels. Draft being the depth of a loaded ship in the water with the measurement taken from the level of the waterline to the lowest point of the hull. They also have a wider beam or breadth.

These two things combined give them their stability which, when combined with their strength, allow them to efficiently push and pull much bigger ships.

But as vessels, ranging from container feeder ships to oil tankers grow increasingly more sophisticated, how is it possible that modern watercraft are unable to maneuver themselves effectively?

That’s despite the fact that these ships and tankers are relatively easily maneuverable on the ocean and they can move forwards and backwards, they still have difficulty making smaller movements and moving sideways - which docking and undocking a vessel requires, particularly when entering or exiting a busy port or narrow waterway.

Other quick tugboat facts

Many tugboats can also travel further out of port and out onto the ocean
Others, however, are designed for river and canal use only - the shape of the hull being the deciding factor
Tugboats carry a crew of anywhere between three to ten or more crew members
Increasingly, hybrid technology tugs or tugboats that run on LNG (liquid natural gas) are being used as a more eco-friendly alternative

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What makes an efficient tugboat?

Whether it’s helping a ro-ro vessel or car carrier navigate a crowded port, a heavy lift vessel or a gas carrier dock, or a passenger ferry navigate a narrow river or canal, tugboats need to meet a certain criteria if they are to be successful.

These are the most important characteristics of an efficient tug.

Maneuverability - tugboats need to be nimble and adaptable and able to change direction quickly.
Precision - tugs need to be able to perform precise maneuvers.
Agility - tugboats need to be able to navigate their way around tight spaces under any weather condition
Strength - it goes without saying that tugs need to have an engine that can generate enough thrust and be powerful enough to be able to push or pull the larger vessel

Are there different types of tugboat?

Broadly speaking, tugboats are split into three different types:

Azimuth Stern Drive (ASD) tugboats
Conventional tugboats
Tractor tugboats

What is an Azimuth Stern Drive tugboat?

An Azimuth Stern Drive (ASD) tug is a kind of cross between a conventional tug and a tractor tug and shares the benefits of both. ASD’s normally have two towing locations - one forward and one amidships and as the name suggests, main propulsion is provided by two rotating azimuth units.

An Azimuth Stern Drive tug is considered to be more efficient than a conventional tug, although less efficient than a tractor tugboat. Other advantages include increased stability when moving at high speeds. Their maximum heel with side thrust is below 15 degrees, this is in contrast to a tractor tug’s 21 degree max heel..

ASDs also have a hull that is designed to operate more safely and efficiently in open seas as well as an average shallower draft of around 3 meters. It is also easy to remove the azimuth units when repair or maintenance is required.

On the flip side, Azimuth Stern Drive tugs can be more cumbersome than tractor tugboats and their control systems can be complex. ASDs can be sensitive to capsizing when utilizing the aft towing position and the vast majority of them are only able to tow using a forward position.

What is a Conventional tugboat?

The oldest model of tugboat, Conventional tugs are built on the earliest principle of tugboat design. These days, however, paddle and steam propulsion are a thing of the past, with these most common of tugs using diesel power and either one, two or three fixed screw propellers.

Tugs that have a single propeller are split into two classes: Left handed or right-handed, with the latter being more common. Conventional tugboats are equipped with a classic rudder, a central towing hook and a power plant complex which is located in the stern.

Unlike the ASD tug, conventional tug boats require relatively little maintenance, making them a more cost effective solution - hence their popularity in port-related maneuvers. Being self-sufficient also means a support system is not required.

However, conventional tugs have less strength, stability and maneuverability than their cousins, the ASD and the Tractor tug and they are unable to work in reverse, unless they are retrofitted with a reduction gear to enable reverse flow. All of this means that they are generally confined to towing smaller commercial vessels.

What is a Tractor tug?

Tractor tugs use a 2-multidirectional propulsion unit. These are either similar to a large rotating outboard motor or a unit consisting of rotating vertical blades. Tractor tugboats surpass other tugs, particularly Conventional tugs, when it comes to maneuverability, mainly thanks to their thrust units being located besides one another and almost under the boat’s bridge.

The towing point of these tugs can also be placed a lot closer to the stern which facilitates maximum output from the propulsion units, making them faster than their rivals. The winch drum which stores the towline is operated by a remotely controlled joystick from the bridge, again affording more versatility and efficiency.

Unlike Conventional tugs and Azimuth Stern Drive tugs, Tractor tugboats offer a full thrust over 360 degrees. It is far quicker to position them and their simple control systems make capsizing a less likely event.

As it might be expected, this enhanced performance does mean that Tractor tugs are more complex - and thus more expensive to purchase and maintain - than the other types of tugboats. Some Tractor tugs also have a high heeling angle of up to 21 degrees which increases the risk of damage when they are alongside a vessel.

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What is a tugboat: conclusion

They might be a fraction of the size of the vessels they help navigate, but this little workhorse of the seas has a vital role to play in the maritime industry. After all, without them, many ships wouldn’t be able to enter or leave ports or even berth.

And that would cause a complete breakdown of the global supply chain. The tugboat is very much a part of the commercial shipping fleet and despite its dimensions, it will still have an experienced ship’s Master (captain) and qualified crew onboard.

Want to find out more about commercial vessels?

From the coaster vessels who ply their trade closer to the shore (hence the name) and within the confines of a smaller area to cable laying ships that keep the world connected and supplied with power to that other small, but essential, watercraft, the pilot boat, we have plenty more for you to explore.

And don’t forget, if you know all about different types of vessels already but are looking for work on a tugboat, or any other kind of commercial ship, Martide is the seafarer job site you can rely on to help you find your next job at sea.

Create your free account and complete your seafarer profile today then take a look through our seafarer job vacancies and apply for any that you are qualified for and interested in.

We hope to see you onboard soon!

Read the previous article in this series: Everything You Need to Know About LNG and LPG Tankers