Ships are gigantic machines with the capacity to carry enormous loads that require heavy lift vessels (HLVs). They transport commodities valued at trillions of dollars all across the world.

But what happens when you need to move extremely massive cargo that is occasionally too hefty for even normal ships?

Moving such cargo could be done for a number of purposes, including transferring other ships around the world or conveying big, dense commodities that cannot be carried on regular carriers. Heavy lifting vessels (HLVs) are useful in this situation.

They vary from traditional heavy-duty carriers in that they can transport loads that would normally jeopardize a ship’s structural integrity. They use cutting-edge engineering and ship design techniques to complete these challenging jobs.

We shall explore the world of big lifting cranes and vessels in this post, as well as the physics that behind their extraordinary lifting abilities.

Heavy Lift Vessel Types

Heavy lifting vessels (HLVs) can be broadly divided into four classes:

• Dock ships
• Open deck cargo ships
•  Semi-submersible craft
•  Project freight carriers.

Semi-Submersible Craft

These are the types of ships that can increase their draft by using ballast water. The ship is lowered deeper into the water as a result, and eventually the upper deck is a few meters below the water’s surface. Thus, “semi-submersible” was coined.

The idea behind these vessels is that items and freight can be carried directly onto the submerged deck by floating them over the resting place. Ballast water is pumped out till the vessel’s deck is raised above the water after they have been properly positioned. The cargo may now be moved securely by the ship because it is resting on the deck.

These ships are frequently used for a few particular kinds of cargo. Included in this are drilling and oil rigs, refineries, factories on the water, dredging tools, offshore constructions, floating dry docks, and other ships that can fit on board.

This type of vessels is built, designed, and constructed very differently from normal ships. For instance, the extreme fore and stern of the deck are home to the superstructures.

At the fore are the crew’s living quarters, offices, and other common rooms. This offers a clear view of the surroundings to the captain and other officers in the bridge. Additionally, it helps with maneuvers and loading tasks.

The equipment needed to run the ship is situated at the other extremity. For instance, the ballast pumps of some semi-submersible kinds are situated here, whilst the marine engines of other types are integrated into this section.

Depending on the design concept and purpose of the ship, each offers a distinct benefit. The ship’s deck spans both superstructures and is very long, very wide, and very flat. This deck is not one continuous sheet of metal since it is subjected to huge loads.

Instead, a number of tiny panels are welded into place and held up by a complex framework beneath the deck.

The hull of these ships often has a short height from the keel to the top deck. This guarantees structural integrity and enables a stronger design for the deck.

Process of Loading and Unloading

Let’s now examine the procedure used to load and discharge floating goods into these HLVs. The operation begins with the upper deck being lowered beneath the water’s surface until it reaches a safe and predetermined depth.

This depth is determined using a number of factors, including the depth of the water in the area, the kind and weight of the cargo, the cargo’s draft, and the HLV’s ballast levels.

Once this depth has been determined, a number of ballast pumps on the lower side of the hull quickly fill the ship’s ballast tanks. The aim of the ballast tanks is to load seawater into particular ship chambers so that the ship sinks into the water.

The tanks on these semi-submersibles are often positioned beneath the deck, between the main structure and support beams. During this procedure, ballast tanks must be filled to the same amounts so that the HLV’s upper deck and keel stay horizontal. If this isn’t taken care of, there’s a danger that the laden cargo will be uneven, will slip off, and will hurt both the ship and the cargo.

The loading procedure can now start after the ballast tanks have been filled to the necessary level. These vessels can only transport floating freight due to their construction. The majority of the time, barges and tugboats are utilized to position the cargo properly on the upper deck.

The connections to the tug boat are withdrawn once the HLV is positioned over the supports, and it starts to progressively pump out ballast water. The vessel is put under a great deal of strain, so it does not fully lift out of the water. To transfer the cargo safely without any water on the deck, it merely elevates itself above the waterline.

One reason not to convey cargo in a submerged mode is that doing so increases the water plane area, a significant hydrodynamic coefficient that raises the vessel’s resistance.

Ship Docking

The semi-submersible class of HLVs and dock ships are similar in appearance and operation. On the port and starboard sides of the ship, there are big side panels that serve as a water reservoir, which is where it differentiates from other ships.

The principal superstructure is often found in the fore. The bridge, quarters, galley, etc. are located here. Typically, the stern portion is left unlocked so that the cargo can enter.

Imagine a floating open-top box with one face missing, which acts as a gate, that can lower itself into the sea in order to visualize how a dock ship looks.

Similar to the semi-submersible class, dock ships operate in three phases.

• Bending down,
• A cargo that is afloat, and
• Rising once more.

The lowering procedure, which involves filling the ship’s ballast tanks up until it starts to sunk into the water, is rather straightforward. However, the walls of the dock hold water once the deck falls below the surface, in contrast to semi-submersibles that keep water from pooling on the deck.

The cargo is floated onto the deck as soon as it has reached a suitable depth. Other ships are the most typical cargo carried by dock ships. These ships are transported or repaired while being carried.

After being hauled into the containment area with the cargo, the tug boat slowly turns around and leaves the dock. The ship then starts swiftly pumping out its ballast water and clearing any standing water from the deck. This keeps happening until the boat is enough above the water.

The procedure for removing the ballast water is crucial and needs to be done with exceptional caution. This is due to the fact that as draft reduces, ships lose buoyancy.

In contrast to semi-submersibles that can have ships anchored, docks can only put such provisions into place once the water has been drained. As a result, supports are frequently affixed to the hull at regular intervals using huge wooden blocks. The ship is fastened to the HLV’s walls and floor once the water level drops.

For repairs, dock ships are frequently employed. These vessels offer an alternative to the use of dry docks situated on land. This is because they do not have to pay the expensive maintenance costs associated with dry docks.

On land, common expenses include repairing the floor and walls, securing the dock gates, maintaining the keel blocks that the ship’s keel rests on, and fortifying the dock’s walls, among other things. Additionally, while dock ships are frequently employed to repair ships that are immobile, ships must arrive at the dry dock for repairs. Additionally, they can maintain and repair equipment while the ship is still at sea.

The replacement of the pumps and keel blocks is the primary repair on ship docks. Derricks and spreader cranes are frequently found on the walls of these docks. These facilitate maintenance by making it simple to carry and move heavy objects.

The ability to deploy ship docks anywhere in the world and their simplicity in customization make them preferable to traditional dockyards. For instance, a number of docks may be floating longitudinally before being fastened. This is done to safely accommodate ships of various lengths.

These docks are designed such that they primarily rely on green water on the deck rather than ballast tanks, in addition to these benefits. This eliminates a number of inconveniences, including the requirement for routine maintenance and tank cleaning. The pumps are the only part that has to be fixed in this case.

The fact that these ships only sail after being cleared of any water on the deck is an essential consideration. This is so that any additional weight on the deck won’t negatively impact the hydrostatics and resistance the hull must overcome.

Cargo Ships with Open Decks

Open deck ships don’t need to have their cargo floated into position like semi-submersibles do; instead, it just needs to be transferred on utilizing cranes that are already on the deck or driven up like ro-ro carriers (roll on- roll off).

Large flat decks on open deck ships can be anywhere from 100 to 300 meters in length. The ship’s extreme fore is where the superstructure, which houses the bridge, galley, and staterooms, is located. Contrary to the design of dock ships, there are no walls to prevent the loading of cargo that is wider than the ship. Compared to the other large lifting ships we’ve spoken about so far, these cargo ships are built differently and have a different design.

Large, heavy structures like cranes, big trucks, construction machinery, yachts, and small boats are transported using open deck cargo ships. The primary need for the type of cargo being delivered is that it can be towed onto the open deck, either manually or with the aid of cranes and tow trucks. Therefore, this class of HLVs cannot move huge ships.

These cargo ships’ structures must be suitably reinforced to withstand the heavy loads placed on the deck. A metal framing web that spans the ship’s whole length and width supports the main deck. The ship has distinct areas beneath this deck for the marine propeller shafts and ballast tanks.

Either beneath this deck or at the foot of the superstructure near the fore, the ship’s engines are situated. The disadvantage of placing the marine engines near the bow is the requirement for extremely long marine shafts. This may result in damage from the engine’s high-speed vibrations or from the shaft’s catenary movement.

The engines should therefore be placed as near to the propellers as possible. The metal sheets that make up the upper deck are joined by welding to create structures that resemble plates. As a result, different areas of the ship can be easily accessed when necessary without removing the entire deck.

To ensure that the cargo is moved safely, the deck typically features equipment for docking and anchoring. These characteristics are crucial because there are no sidewalls to provide protection. Pad-eyes are widely used because they make it possible to connect several structures to the deck directly.

The ship’s stern has a sizable ramp made of reinforced material that spans the ship’s beam. Vehicles and cargo can travel to and from the main deck via this ramp. Large ships occasionally have smaller ramps on the port and starboard sides to allow for multiple cargo loading. These HLVs are frequently categorized as Ro-Ro carriers for heavy-duty freight.

Project Carriers for Cargo

Project cargo is a specific term used to describe big, heavy items that are frequently expensive or essential to a certain sector of the economy. They are cumbersome, cannot drive themselves up ramps, cannot float, and cannot be transported in intermodal containers. Cranes must be utilized in this situation to assist in loading and unloading the cargo.

Unfortunately, the location of the majority of the cranes at the port prevents them from moving these commodities effectively. If the ship had its own set of cranes that could raise this kind of cargo, it would be much simpler. And project cargo carriers provide that purpose. They carry heavy items onto ships using cranes that are built into the ship’s deck in order to convey them.

These ships’ designs frequently change depending on the kind of cargo they are intended to transport. For example, supports are frequently offered so that pipeline and bridge sections can be balanced on the deck.

The deck is mostly flat and has no protrusions. Compared to typical HLVs, these ships sail at a significantly lower draft. They typically have to lower their cargo into holds below the deck, which explains this. Two huge maritime cranes are typically available to help with loading and unloading. These are located in the front and rear of the vessel, typically on the port or starboard side.

As a result of the weight being concentrated on one side, the ship tends to become more unstable. However, lifting long cargo that needs support from both ends won’t be possible until the cranes are paired. The ballasting procedure is crucial for balancing the crane weights and must be carried out correctly to guarantee that the vessel is steady.

In order to effectively support the cargo cranes and give the ship torsional rigidity, the side hull has been reinforced. Additionally, several types of project freight carriers require that the cargo be stored on a flat continuous deck. Such boats maintain a deep draft to guarantee adequate stability.

However, there is a good likelihood that the cargo will try to roll over the deck in the case of an accident. This may result in a sudden imbalance that could cause the vessel to capsize. So, when tying the cargo to the deck, sufficient care must be exercised. When the weather is choppy, heavy-duty pad-eyes are frequently utilized, and blocks are positioned on both sides to keep the cargo from rolling over.

Project cargo ships typically measure only a few hundred meters in length, making them smaller than other HLVs. They compensate for this by being able to transport very large goods that can be challenging to load on other HLVs. Large vehicle parts, pieces of industrial buildings, crane and bridge sections, and pipelines are typical examples of project cargo.

With roughly four times the pulling power of standard deck cranes, the two cranes work in tandem to raise massive loads. To stabilize the entire vessel, however, the ballasting procedure is essential. These vessels are crucial in the global transportation of big project cargo.

The conclusion

Large ships called heavy lifting vessels (HLVs) are able to transport other ships, big industrial equipment, floating plants, etc. They do this using four major methods and are able to deliver cargo that other types of ships cannot.

It’s critical to keep in mind that adequate ballasting and balancing are absolutely essential to the stability and balance of these types of ships. They carefully load and unload their valuable cargo at the port as a team.

They are among the most powerful buildings ever created and play a crucial role in trade and commerce. It would be nearly difficult to provide countries with critical and necessary commodities and supplies without these vessels.

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