Without a power source and propellers, cruise ships would drift aimlessly at sea. These mega-ships require engines, fuel, and massive propellers just to move through the water and keep all activities on board the ship running. We describe not only the cruise ship propeller size, but also how it integrates with the rest of the engine.

Older cruise ships use diesel engines for propulsion. The power generated from the engine goes through a transmission and into the propeller shafts.

The transmission determines propeller revolution like the transmission in an engine transfers RPM to a manageable speed to power the rear wheels in a car.

Meanwhile, modern cruise ships use diesel-electric engines or gas turbines to propel the ship through water. The ship’s systems are also used to guide and move the ship through the ocean.

The larger the ship, the higher the demand for electrical power. There are cruise ships that rely on two different sources of power. One is dedicated to electrical power, while the other is for propulsion.

Cruise Ship Propeller Size

Propellers can be up to 20 feet in height. Often referred to as ABB Azipods XO, modern cruise ships tend to have three of them to properly maneuver the ship and propel it forward in water. They are efficient on fuel compared to a traditional system.

As mentioned, they allow for improved maneuverability, allow the ship to maximize speed, reduce bad emissions, and optimize the overall performance of the cruise ship.

An ABB Azipod system has a large impact on the operating efficiency of a cruise ship. It effectively reduces bad emissions and energy consumption by 20%. This propulsion system resides in the ship’s aft outside of the hull. They can rotate by 360° using a rudder, which provides thrust in any direction. This is not possible with a conventional system.

This type of propeller contains three main components:

• Frequency Controller – This is designed to change the supplied power’s frequency, so the rotating motor speed is more easily controlled.
• Supply Transformer – The power, which is produced by a generator, is 6,600 KV. This is stepped down to the required voltage used by a supply transformer. Then, it is transferred to the motor located in the pod.
• Propulsion Motor – Designed to drive or produce thrust, its rotation is generated using an electric motor.

How Do Propellers Work?

Propellers are required to push a cruise ship through water. Commonly referred to as “screws,” they slice through the water. They also provide a reverse and forward motion. Cruise ship propellers do not need to turn quickly since they rely on brute power or torque instead of high speeds or RPM. This is what causes a ship to move slowly, as these vessels rarely reach 30 knots.

Cruise ships that are newer and more cutting edge may use azimuth thrusters. These are pods housing propellers, which rotate 360° and provide optimal maneuverability. They were designed to replace rudders and are touted as more beneficial compared to screw-type propeller systems. Benefits include improved fuel efficiency and shorter stopping distance.

These types of propellers allow cruise ships to turn quickly in water when necessary to avoid collisions, which is why more vessels are being equipped with this technology.

How Do Azipods Work Compared to Traditional Propulsion Systems?

The term “Azipod” combines the words “azimuthing” and “pod.” The phrase “Azipod” is a registered trademark of ABB Oy. They work by having the propeller located on the front of its pod. This allows the cruise ship to be pulled through the water rather than being pushed as in a traditional shaft and propeller system.

With a traditional system, its propeller is rotating in water that has been disturbed by the moving of the propeller shaft, brackets, and framing. With the pod system where the propeller is found in the front of its pod, it is turning in water that has been undisturbed. This allows the pod to be 5%-6% more efficient due to improved water flow.

Traditional systems are noisier when maneuvering due to the cavitations of its propellers. This doesn’t occur with pods since they are tractor pods. Tractor pods comparatively pull a ship through surrounding water. Clean, smooth water moves into the blades, thereby decreasing noise.

Pod systems free up additional space in the hull. Traditional systems meant the motors and propeller shafts had to be placed in the hull. Modern cruise ships not containing pods require stern thrusters to maneuver the cruise ship while undocking and docking.

On the other hand, pod systems use the equivalent of a drive motor and propeller shaft, which are found in the pod as opposed to the hull. There is also no need to use stern thrusters.

Many cruise ships contain two pods. Allure of the Seas and Oasis of the Seas contain three pods. Several may be designed using a combination of azimuthing pods and pods which don’t rotate (fixipods) for forward/backward motion.

What Is Propeller Cavitation?

This is the formation and dissolving of vapor bubbles (vapor filled voids) found in liquid mediums. Since the propeller rotates through water at an angle, a suction and pressure side exist on each of the propeller blades. The faster a blade slices through water, the lower the pressure becomes with the suction side.

At a certain speed, the pressure found on the suction side will become so decreased that water running over it will evaporate. When this occurs, voids or vapor bubbles form. It occurs at a normal air pressure (1013.24 hPa) with the water evaporating at 100°C. At higher pressures, evaporation temperature also increases. The opposite happens at lower pressures.

When local pressure goes down below vapor pressure, the water will evaporate. Then, a cavitation bubble forms, becomes bigger, and is transported by flowing to an area with higher pressure. The bubble then ceases to grow any further. When local pressure exceeds vapor pressure, the vapor will condense, beginning from the bubble’s wall.

Eventually, the surface breaks down, beginning with the weakest location, thereby causing the bubble to implode. While it is imploding, water fills the space where the void is, causing a pressure surge. This creates pressure waves along with high-pressure peaks.

Should the vapor bubbles be close to or directly on a solid wall surface like the blade of a propeller, the implosion generates a liquid microjet exerting high stress on the surface. This sudden energy release creates pressure loads found on the surface, generating crate-shaped erosion of material in a propeller blade.

The bubble layer pack on a surface of a blade will also make them thicker, thereby increasing resistance moving through water. This impacts the propeller’s performance. Cavitation also generates vibrations and popping noises. This, in turn, affects guests and ships.

What Causes Cavitation?

The primary cause of cavitation is an unevenness in the blade’s leading edge, too much sharpness of the edge, increased curvature of the propeller blade, or poor finishing of the surface of the blade.

Effects of Cavitation on a Cruise Ship’s Propellers

The effects on the propellers are:

• Noise
• Vibration
• Eroding of the blades
• Decreased performance

Noise

As cavities collapse, they generate noise and high-frequency vibrations. This can be unpleasant to crew and passengers if they are located at the aft of a cruise ship.

Vibration

Vibration is generated from the unsteady characteristics of cavitation. It is the periodic deflections of the propeller in a horizontal, vertical, or torsional manner.

Vibrations are further reduced by using Schneekluth or Mewis ducts. These are fitted on the hull of the ship, or before the propeller. This provides a uniform wake flow into the propeller thus reducing vibrations.

Erosion

This can be a serious effect. Cavitation bubbles once formed are unable to persist if they move into an area where net pressure goes back to a value which exceeds the water’s vapor pressure. It can happen toward the blade’s trailing edge or as it moves from top to bottom of its circle, thereby gaining hydrostatic pressure.

The way they collapse creates a new phenomenon. Bubbles will then contract to minute sizes prior to disappearing. This causes the entire energy to collapse, causing a change of state to be concentrated into a tiny location.

At the beginning, the damage looks like it has been hit with a tiny hammer, leaving small, circular indentations. If the damage is prolonged, the result is serious pitting in the metal. This looks like a definite crater on the blade’s surface. Continual pitting can erode the entire thickness of the propeller blade, creating a hole.

Performance

When it comes to performance, the impact can be considerable. Cavitation begins at the tips of the blades and gradually consumes the remainder of the blade as propeller loading increases. As cavitation extends to .75 of the radius, there is significant loss in the thrust plus a reduction in torque. There will be a significant increase in revolutions with a given power.

Thrust breakdown will begin quicker than a change in the torque. This can result in a loss of efficiency.

How Is Cavitation Prevented?

The hull of a cruise ship influences the flow going around the propellers since they fully work in a cruise ship’s wake. To avoid this, the follow measures are undertaken:

• Reducing revolutions per minute. Since the thrust varies, reducing revolutions decreases cavitation. However, the downside is a loss of speed.
• Generate a maximum immersion.
• Reduce the blade’s thickness. This is done by utilizing stronger materials, which are resistant to cavitation.
• Avoid suction peaks close to the leading edge. This is done by utilizing a suitable amount of camber and a good shape for the entrance.
• Design the stern so that it achieves a uniform wakefield.
• Avoid high sections on the blade’s backside. This is achieved by using section shapes providing a uniform pressure distribution.
• Pitch can be varied over the blade’s length. This diminishes loading in important areas.
• Decrease angles of incidence and blade angles by creating a slightly bigger diameter.
• Make the total blade area larger. This is done by increasing the propeller’s diameter with a reduction of revolutions or your blade area ratio with a constant diameter.

Which Cruise Ships Have the Largest Propellers?

Royal Caribbean’s Oasis Class

These cruise ships tend to be the largest in the world. Their propellers are designed to have a diameter of six meters. The ship’s propulsion contains three 26,800-horsepower Azipods, which is an electric azimuth thruster.

How Fast do Propellers Spin?

Since a cruise ship’s engines turn their crankshaft at extremely high rates of speed – hundreds or thousands of revolutions per minute – the engine connects to the ship’s propellers using gears. The propellers themselves are created to turn slower, which tends to be around 250 revolutions per minute or less.

Carnival Cruise Line Fantasy Class

This cruise line’s service speed is 22.3 knots. It was the first to use a unique electric azimuth Azipod system for propulsion. This means that the ship is pulled as opposed to pushed by its propeller. The Carnival Elation contains two 14 MW Azipod units.

Conclusion

When it comes to a cruise ship propeller size, they can be as large as 20 feet high. This is no surprise when you consider the size of the engines and everything that is necessary to move a ship. Thanks to the introduction of Azipods, cruise ships are better able to navigate around any obstacles they may encounter in the water.

Read Also: How Big is a Cruise Ship?

Not only are they better equipped to move around potential hazards, but this improvement in technology also allows them to better move into ports, work more efficiently, and save on fuel costs. With constant pressures to become more environmentally friendly, this may be a good thing for cruise lines.

While they aren’t great for the environment, they aren’t emitting as much pollution as fuel is being conserved. It also makes this natural resource stretch for a longer duration. Ideally, LNG-powered cruise ships can be used to prevent harmful emissions. This is the best method to protect the environment.

However, with the drawbacks of using this fuel type, changing the propulsion technology may be the next-best thing.

Whether you are curious about a cruise ship’s engine or simply want to avoid the cabins surrounding this noisy area, an engine room can be an interesting place.

We outline what is contained in the cruise ship engine room, what it does, and how much noise and vibration is generated in this area.

Where Is the Engine Room Located on a Cruise Ship?

On newer cruise ships, engine rooms are found on the aft of the ship and on the lower decks. They are not fully at the back but closer to mid-ship.

Regardless of the ship’s size and type of engine, engines are extremely loud. Engineers compensate for this fact by incorporating sound reduction features and technology to keep the room well insulated, so it is less noisy for guests.

Insulation, in this case, provides a dual purpose. It reduces noise and keeps the heat generated by a fully operating engine from coming out on adjacent decks. On a cruise ship, this is very important, where comfort is one of the cruise line’s top priorities.

How Noisy Is the Engine?

The decibel range for the engine of a standard cruise ship exceeds 173 decibels. This is extremely loud and within a range that can damage hearing in seconds. Thanks to proper insulation and sound-reducing features, it won’t sound that loud.

If you are in the engine room while the engine is running, it will still be very loud regardless of what noise-reducing technology is used. To put it in perspective, those who enter the room are required to wear hearing protection. Otherwise, they can experience hearing damage.

However, guests don’t have to be concerned if their cabins are in this area. The noise level will not damage your hearing because the surrounding cabins are well insulated. However, you may still be able to hear the noise and experience vibrations through the walls and floors.

As mentioned, the engine does make vibrations while it operates. They can be felt in the surrounding areas, including cabins that are adjacent to them. It may cause coat hangers to rattle or other items in the cabin to shift, which may disturb your rest.

How Big Is the Engine?

Modern cruise ships have more than one engine. The largest ships, like the Oasis class from Royal Caribbean, contain six engines. Other ships – like the Carnival Splendor of Carnival Cruise Line – may only be just four, depending on the size of the ship, its age, and the cruise line.

The engine room itself is expansive and covers several decks. Space is needed not only for the massive engines, but for fuel tanks, generators, the engine workshop, and the control room.

How Does Heat Escape from the Engine Room?

The heat from the engines is removed by a series of heat exchangers. This is found on the exhaust path proceeding the turbocharger on the way to the scrubber. Exhaust gas reaches a temperature of 663°F yet is continuously cooled using heat extraction until it reaches 86°F when it comes out of the funnel.

The engines are fuel- and heat-efficient. The recovered heat is used for numerous services, including desalination of saltwater to fresh water and fuel heating (if heavy fuel oil is used). Fresh water can be produced by reverse osmosis to supplement an evaporator.

Where Is Fuel Stored?

Fuel is usually stored in double-bottom tanks. They are distributed across the length of the cruise ship with ballast tanks. The only fuel tanks located in an engine room are service and settling tanks.

What Are the Cabins in this Location Like?

Most people shy away from this area due to the noise. However, there are other reasons why these cabins are less desirable besides the fact that they are noisy.

Cabins near the engine room may be:

• Smaller than average cabins
• Not contain windows
• Receive engine noise
• Be prone to vibrations, most notably while docking

These rooms tend to be cramped and small. They are also not priority rooms within the ship’s design. Booking this room may mean you will experience vibrations and noise from the engine. You may hear the crew as they go back and forth to the engine room throughout the day and night. 

These cabins are in the lower deck and in the middle of the ship. They tend to be windowless and dark. Rooms located in the center of a ship generally don’t contain the luxury of windows, so it may make people feel claustrophobic.

Are There Any Advantages?

Some people argue that most people don’t spend much time in a cabin – they are too busy exploring the cruise ship. There is plenty to do onboard, and if you enjoy the social scene, you may not spend much time inside the cabin other than to sleep.

The main reason people select an inside cabin on a lower deck is that they are less expensive. Most people book a cruise to have an experience – not to sleep. Additionally, what most people don’t know is that if you book a cabin near the engine room, you may have the option to upgrade.

An option to upgrade doesn’t necessarily mean that more money will be required. It does mean that if a better cabin is available or is vacant, as in the case of last-minute cancellations, you may be upgraded for free. However, this is not guaranteed.

The engine room truly is the heart of the ship. It is where crankshafts, pistons, and hammers rotate to make the ship move forward. The chief engineer and crew work 24/7 to ensure the entire ship operates smoothly. It permits luxuries onboard like electricity, plumbing, and air conditioning to function.

Aside from housing generators and engines, pumps and heat exchangers are located here to cool the engine and stabilize motors and fins, in addition to the bow thruster system. Since equipment depends on electricity, modern ships contain backup generators on the outside of the main engine room in the event of a fire.

Read Also: Future Fuel – What Is an LNG-Powered Cruise Ship?

Generators power all the vital functions to run a ship, like emergency lights, communications, and navigation systems. If the generator fails, then there are also backup batteries that can be used for short periods of time.

All this machinery is overseen by the Engine Control Room, which contains lights, screens, alarms, and switches where every piece of equipment can be monitored to ensure the cruise ship runs smoothly.