Work on a very large gas carrier "Very Large Gas Carrier"
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As the world strives for cleaner fuel sources, it becomes critical to be able to ship and transport these sources from large reserves and fields to the countries where they are used. The growing demand for liquefied gas fuels often creates problems due to the limited size of most LNG carriers. Large LNG carriers (referred to as VLGC tankers) are a subclass of typical LNG carriers designed to carry significantly larger volumes of gas.
Most frequently transported cargo
In general, the most frequently transported cargo is liquefied petroleum gas (LPG), which is produced from oil reserves, and liquefied natural gas (LNG), which is produced from hydrocarbon deposits alongside fossil fuels.
In order to build massive ships capable of transporting large quantities of volatile gases, it is important to evaluate various aspects of the safety of the carriers. In addition, since we are dealing with gases and liquids that are more difficult to move, there must be appropriate loading and unloading mechanisms. While solids can be easily moved with taps, liquids and gases must be completely drained at the discharge port. Any residual substances can contaminate any incoming cargo.
VLGC tankers are typically around 250-300 meters in length and contain four to six storage tanks located along the centerline. Tankers-VLGCs have a double bottom structure and an additional side shell in some carriers. The purpose of having multiple hulls is to contain the leak as well as provide space for vital ship components.
Most of the electrical wiring and piping required to operate the ship runs inside this shell. Often the double bottom also has a streamlined keel to allow main connections and wires to pass through the entire length of the boat.
All the components needed for the tanks to function are located in a large dome built on top of each tank. Tank systems on VLGC tankers consist of the following components: primary barrier, secondary barrier (optional), bulkheads, insulation and support structures.
The primary barrier is the reservoir itself, which can vary in shape and size. Common tank types are prismatic (class "A"), spherical (class "B") and cylindrical (class "C"). The most suitable class is the prismatic tank, as it allows the use of large holds for transportation by conforming to the shape of the hull. Spherical tanks are often enclosed in a vertical skirt that secures the tank to the body. This provides the tanks with additional support elements.
Finally, Class “C” (cylindrical) tanks can be arranged either transversely or longitudinally, although blade designs are also common. All of these tanks also have longitudinal bulkheads that run along the length of the tank. They reduce the splashing effect resulting from the free surface effect (FSE), which is known to drastically distort the stability of the boat.
Membrane construction
In addition to the self-contained tank-based system, there is also a membrane design that is used on some VLGC class ships. These membranes are used to regulate the cargo between the different holds of the vessel and significantly speed up the loading and unloading process. However, the biggest problem with membrane structures is that they are not resistant to strong vibrations. As a result, they are not suitable for use in regions with poor weather conditions.
Experiments are currently underway with membranes with special stiffness. However, today, stand-alone units continue to be the usual means of transporting these types of cargo.
Crewing company Marine MAN Ltd ®, in partnership with the large ship-owning company "Eaglestar", invites experienced Ukrainian sailors from among the senior officers to work on tankers (VLGC). High wages and state-of-the-art ships will ensure upward career development. Send your CV and application to cv@marineman.eu.
