Types of Tugboats & Everything You Need To Know

by | Last updated Nov 24, 2023 | Ship Types, Vessel Information | 0 comments

Tugboats are the most underrated ships on the entire planet. They work hard, do a lot of unimaginable things, and keep vessels from making a mess. 

But despite their best efforts, it’s always the huge merchant ships that take the spotlight.

We get it. In this industry, size matters a lot. The bigger, the sexier! And tugs being small, isn’t just as grandiose as compared to them.

But do you know that some of these tiny, low-freeboard, funny-looking tugboats have a price of more than $20,000,000?

Some companies are paying that much because they know that these boats are not to be messed with.

They know the reasons why they are called small titans. Despite the size, these floating tractors are all muscles, strength, and maneuverability. Plus they have indestructible winches, too.

What are Tugboats?

Tugboats are small but powerful boats that push, pull, or tow other ships (or barges) that can not maneuver safely on their own.

To “tug” means to pull, jerk, wrench, heave, or yank.

Mega ships are built for cruising huge distances with plenty of sea room around. But when it’s time to dock in ports, their movements are constrained due to their enormous size.

Tugboats help these vessels dock safely.

Aside from that, there are tugboats designed to venture into open seas for rescue, tow huge platforms or other vessels, and assist in anchor handling.

On the north, they can perform icebreaker duties, especially in the harbor when docking a ship.

A map showing a busy harbor where huge ships are able to pass even if there are only small clearances.
Lots of ships of different sizes within rivers and terminals.

If you ever visited major ports, you might wonder how huge vessels dock deep within terminals. It’s even more head-scratching when you see the hurdles they overcome. 

Imagine those crisscrossing traffic, narrow channels, and tight bends that look impossible to pass.

Mind-blowing, isn’t it?

Well, the key to all of that is with the help of tugboats.

A Tugs Partner

Tugboats- or tugs are specially designed for strength. But they don’t push or pull a ship on their own preference. 

They rely on someone to coordinate their maneuvers especially if they are working with other tugs.

To get the job done, tugboats await the Pilot’s command who is aboard the bigger vessel. Just take a look at the image below.

Four Tugboats Assisting a Huge Tanker during maneuvering.
Four tugboats assisting a huge tanker.

Because of their small size, tugs do not have a bird’s eye view of the situation. The Pilot, on the other hand, can see everything and has full control of the ship’s engines and thrusters.

Thus, tugs are able to coordinate what to do, when to pull, how much power to give, and in what direction.

Emergency brakes

Tugs are pure muscle and steel. They are built for quick response, sheer power, and maneuverability.

When made fast to a vessel, they help her turn 360 degrees with ease. If the swing becomes uncontrollable, tugboats are there to stop it.

Additionally, they function as a secondary rudder or as an emergency brake. I often observe this one when the ship is approaching the lock or berth and there is a strong current.

How can tugboats pull so much?

There are three major components that tugboats have to get the job done. These parts work hand in hand to give the needed force when assisting other vessels.

1. Tugboat engines

Most tugs have two diesel-powered engines which run the propellers. But they are not ordinary engines. They are very powerful, enough to deliver the required power needed to perform their duties.

“A tug’s power is measured in Bollard Pull (BP). When you go around a ship, you may notice that there are safe working loads (SWLs) marked on bitts, chocks, and fairleads.”

“These markings indicate the amount of force the fitting can take without damaging it. And even if tugboats have a bollard pull greater than that of the markings, they can still adjust their power since they have sensors attached to their winches.”

Don’t underestimate them. Each of their engines can power a full-size locomotive. Because of their herculean strength, tugs aim for the “tug area” of a vessel’s side when pushing.

Their propellers also vary depending on their designs which we will tackle later.

The strongest tugboat in the world, the Island Victory, has an engine capacity of 8,000kW and a max bollard pull of 474 tons!

2. Tug’s hull shape

Compared to other vessels, a tugboat’s hull is not designed for speed. Even the strongest high-performance multi-purpose tug only has a top speed of 14 knots.

A huge part of it is submerged and when they power up, they sink even further. This provides more water for the propeller, increasing the traction and thrust.

Their speed may be slow but even if they are travelling at six knots, they pack a punch that can pull a hundred elephants.

The hull design is also built for maneuverability. When combined with its powerful engines, tugboats can move in any direction in a matter of seconds.

A tugboat pulling a ship while her line is made fast on the ship's stern. You can tell the tugboat's power in that image by looking at the line.
“Tugging” the ship.

3. Indestructible winches

Their hull and engines, no matter how powerful they are, won’t reach their full potential without their indestructible winches.

This may sound like an overstatement but I haven’t heard of tug winches getting destroyed. I only saw towlines, fairleads, or bitts getting mutilated by the raw power of tugboat action.

Today’s generation of tugboats are even built better. The latest ones have winches that can rotate 360 degrees around the tug itself.

Purpose of Tugboats

Tugs perform a variety of tasks, the most common of which are the ones described above. But they also execute other important jobs depending on their design,

They can be used for salvaging dead ships on the heavy seas. Additionally, some designs can tow huge oil platforms at great distances.

If something at sea or in the harbor is on fire, tugboats have water canons for firefighting. They can escort big ships and act accordingly if something bad happens to them.

In one port, there was this barge that lost its steering and was running toward us. It was clear that he would soon hit our starboard side and we couldn’t do anything about it because we were moored. Suddenly, a tugboat appeared out of nowhere and prevented it from happening.

Lastly, there are tugboats used to transport cargo. They are usually made fast to dumb barges and delivered to some terminals within the harbor.

And there are tugboats that can do all of those things and more. These are called multi-purpose tugs and are usually built huge.

Harbor tug towing dumb barge
A dumb barge.

Well, since I mentioned it, dumb barges are barges without engines. Think of it as a floating box. They can’t move on their own but they are useful for transporting goods.

That’s why they are made fast on tugboats for transport.

Types of Tugboats

Just like various types of ships sailing the seven seas, tugboats are also categorized based on the purpose or function they perform. 

Their design depends on the type of jobs they do and the environment they operate.

But all of them have the same denominator. They are nimble but very powerful. They are built to assist other vessels. And their durability enables them to handle huge amounts of loads.

Furthermore, they also have strong water canons that help in firefighting.

1. Seagoing Tugs

Also known as deep-sea tugs or ocean tugboats, seagoing tugs are built to stay longer in the open sea. They are the much bigger and stronger type and manned with more crew on board.

A very well-known type is the salvage tug which assists disabled ships or those that run aground. They are also called Rescue Tugs.

Powerful tugboat ALP Striker towing an Oil Rig.
Towing an Oil Rig.

Others tow log rafts a few hundred miles to the sea. Meanwhile, oceangoing tugs move the largest and most valuable objects afloat like drill rigs and FPSOs.

2. Escort Tugs

Another category of tugboats that are essential in every port is escort tugs. Escort tugboats provide aid to vessels navigating within the confined spaces of a port.

Since mega-ships are inefficient in shallow waters and restricted terminals, escort tugs are there to provide extra “oomph”. When attached aft of a vessel, they act as emergency brakes and emergency steering.

These boats are highly maneuverable but very powerful indeed. They take on ships a thousand times bigger than their size and usually work in teams with other tugs.

Since the deployment of Escort tugs, the number of shipping accidents when entering or leaving port and navigating along narrow channels has decreased dramatically.

An escort tugboat sailing closely from behind a mega container vessel transiting in a narrow channel.
An Escort Tug.

3. Harbor Tugboats

As the term implies, harbor tugs are multi-purpose tugs working within the harbor. Their size is smaller compared to the previous categories but carries many functions within the port.

Most often, they help in maneuvering vessels to their position in and out of the terminals. But they are always seen towing or pushing “dumb barges”.

These barges are laden with ore, wood, containers, sand, even mobile cranes, and many others. 

Since huge ships are not capable of sailing in inland waterways, harbor tugs deliver the goods to these areas using flatboats.

Another important role harbor tugs have is firefighting inside the port facilities. Why not? They are floating on top of an unlimited source of extinguishing medium.

A harbor tug pushing a dumb barge across the River Thames.
A harbor tug pushing a dumb barge.

4. Tractor Tugboats

Another category of tugs that can either be an escort or harbor tugs are tractor tugs. The definition may be confusing for this one but we will sort this out.

Tractor tugs are identified as those having their propeller units forward of the center line. They can either be Z-drives or Voith Schneider types. We will discuss their propulsion below.

Years ago, any tugboat with units aft of the center line was called “reverse tractor tugs”.Another definition for tractor tugs is that their main duty is to supply maneuvering and or docking traction for vessels lacking that ability.

Thus, you can see them assisting huge vessels during mooring operations.

A tractor tugboat pushing a vessel to get it alongside
A tractor tugboat.

Types of Tugboat Propulsion

They all may look the same on top but below the waterline, their design differs significantly.

This is because the propulsion system evolves throughout the years as technology improves and more efficient schemes are discovered.

As we mentioned earlier, bollard pull is the measuring power of a tug’s strength. Achieving that requires the propulsion system to be powerful as well.

Here are the top most common propulsion systems.

Conventional Propellers

As the word itself, conventional propellers are the predecessors of modern types. They are sturdy and have the simplest design.

Early tugs are made using this type. A propeller shaft which is connected to the engine on one end also has the propeller on the other end which is submerged in the water.

Compared to others, they require less maintenance and are suitable for ocean-going tugs.

Conventional Tugboats design are similar with ships where a propeller shaft from the engine connects the propeller.
Conventional Tugboat.

The problem with conventional systems is their maneuverability. Since the propeller is fixed, the engines must stop first and then reverse to go astern.

There’s also a delay in its maneuvering since it uses rudders that have limited angles to turn the ship.

Hence, they are slowly being replaced by more advanced types like the Z-drives and Voith Schneider.

Azimuth Stern Drive Propellers

Also known as Z-drives, ASD tugs are so special that their two propellers can turn 360 degrees independently. That’s why they are called Azimuth propellers.

They are positioned side by side under the aft part of the tug. To make them more effective, each is fitted with Kort nozzles for greater thrust.

This enables faster maneuverability than conventional types as it can move in any direction. Because of this, they are built with towing winches/ hooks on the forward and aft parts.

A tugboat fitted with Z-drives navigates through the river.
An Azimuth Stern Drive Tugboat (ASD Z-Drives)

Z-Drives are very agile and can transfer from one side to another side of the ship in a short period. You may not know it but you have most probably witnessed this type of tugboat action.

A faster response could mean life or death, especially during emergencies.

Voith Schneider Propeller (VSP)

Voith Schneider Propeller is a specialized propulsion system that transcends the traditional designs of tugboats and even most ships in general.

Tugboats with this arrangement can change any direction nearly instantaneously. It can go from full ahead to full astern in a matter of three seconds!

Finally, a technology that catches up with the rest of the world.

A rendered image of a tugboat fitted with Voith Schneider Propeller forward of the underwater hull.
Voith Schneider Propeller

Angle of Attack

The secret lies in its design. Unlike other propellers which are installed on the vertical axis to direct their thrust, VPS has vertical blades that can change its “angle of attack”.

The blades are arrayed in a circular fashion and revolve in a single direction. To direct the movement of the tug, the blades’ angles are changed while revolving around the plate to create thrust.

By controlling the angle of the blades, you can turn the boat on the spot. Hence called the “angle of attack”.

You can move the boat sideways (or in any direction) without turning it around. This feature is very useful in tight spaces.

Careers on Tugs

Depending on the categories and size, tugboats are normally manned by four people. Their working schedules are quite different than merchant vessels. 

Some of them have a seven-day on-and-off contract while others take on a three-month basis.

Different tug types have different salary brackets just like other salaries of seafarers. Harbor and escort tugs are normally manned by 4 crews: Deckhand, Chief Engineer, Chief Mate who acts as the second Captain, and the Captain.

Salary

A deckhand’s salary is about $1,000 per month. Sometimes, it reaches a high of $2,400.

Chief Mate and Chief Engineer are at $4,500 and $6,000 respectively.

Meanwhile, a Captain earns $8,000 per month.

The salary is dependent on many factors. There are various seaman online job sites to get a grasp of the available positions for various types of boats.

Tugboats: An Economic Engine

Tugboats are an indispensable part of our shipping industry. They are small in size yet their power and versatility contribute to the safety of ships going in and out of port.

These little giants are a proven component of our economic engine. Without them, huge vessels may not be able to dock safely.

May the winds be in your favor.

Gibi

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