Bunker Ships: The Solution for Midsea Refueling Challenges

Bunker Ships: Ships sail thousands of nautical miles across vast expanses of ocean between ports of call, especially those used for transcontinental transit. In addition, ships are large, heavy constructions that need a lot of power to move forward after they have overcome the resistance of the surrounding water, including frictional resistance and wave-related resistance that are always present in seas and oceans.

In addition, because they have to sail for extended periods of time, they require a constant power source to meet their various energy needs for operations, maintenance, and comfort. And the first thing that comes to mind when considering the cost of power for whatever purpose is the necessity of fuel or a supply source. As a result, during a ship’s journey, a large amount of fuel must be kept in its fuel tanks. There is never anything that can be considered safe or sufficient when it comes to storage or reserves.

On a long weekend, you decide to take your automobile to a favorite destination for a traditional lengthy road trip. You fill up your petrol tank completely before you leave and get going. You are certain that you will come across a lot of gas stations or fuel pumps where you can always fill up. But let’s say if, due to indifference or an unpleasant and unanticipated betrayal of your so-called trustworthy GPS map, you end yourself getting lost and traveling in circles on an unknown, dark road. Your car is about to come to a complete stop since your tank is practically empty!

To exacerbate matters, there is no network service for your phone, so you are unable to call for assistance! In a short while, a bear can appear out of nowhere and crash into your glass, or worse, a group of thugs with weapons and knives might besiege your automobile!

Depending on the length of your trip and the size of your automobile, it makes sense to carry a barrel or, at the very least, a jar of petrol if you really want to avoid these terrifying stories. The worst-case scenarios should be taken into account while evaluating the risks involved in any given circumstance. Naturally, you are powerless to stop it if you have a string of flat tires or an engine that won’t start!

In a similar vein, ships that travel great distances use a lot of fuel. Numerous variables, including ship type, size, route, length of travel, and weather, affect this usage. On average, a cargo vessel of average size uses more than 100 metric tonnes of voyage each day while at sea.

In the case of passenger ships, this number is larger for a vessel of the same size because these vessels have a very high power requirement to support the passengers and amenities (referred to as hotel loads in technical parlance). A large transcontinental passenger ship must use a few hundred metric tons of petroleum every day! Similarly, because of its size and numerous onboard equipment, such as heating systems, a huge crude oil tanker has to consume several hundred metric tonnes of petroleum.

In the early stages of design, a designer determines the fuel oil capacity and the related tankage depending on variables such size or displacement, engine type, speed, and, most crucially, range. The range is the furthest a vessel can go while carrying its entire load and not refueling to its maximum capacity from the coast.

Let’s say that a vessel has an R-designated range. If so, it is allowed to travel to ports of call that are located within that specific range R’s nautical radius. During the design phase, this range is estimated while simultaneously accounting for a safety buffer that maintains the value below the maximum distance the vessel may be technically able to cover at full tank capacity.

The Idea Behind Bunker Ships

Bunker Ships
(Credit: Wikipedia)

Even though a vessel’s tankage capacity is self-sufficient from the outset to operate within a certain range, challenges or deviations are never completely inescapable. During the course of its design lifetime, a vessel may require urgent midsea refueling.

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A detour from the planned route due to bad weather, choppy seas, or other safety concerns, the need to travel a greater distance because of a challenging requirement, or—most importantly—unexpected fuel loss from a tank or tanks as a result of accidental damage or breach—are just a few of the numerous reasons why this might happen. So what are the options in these situations?

Bunker Ships Fueling

A ship with a specific displacement design value cannot afford to have extra fuel on board. While many designs allow for the storage of additional or excess fuel tanks, those are all part of the onboard capacity and their depletion is frequently seen as part of the risk profile. Thus, the fuel supply from outside sources midsea is the solution. Additionally, the term “external sources” refers to bunker ships, which are ships that carry oil and provide fuel.

cost of fueling a cruise ship, how much does feul cost on a cruise ship
(Credit: DNV)

The concept is comparable to midair jet refueling, which fighter, military, cargo, and even passenger aircraft use as necessary. Because it occurs at such high altitudes and with both the supply and receiver aircraft traveling at such high speeds, midair refueling is a far more difficult procedure. Although it is still a very important procedure in vessels, it is much simpler because both float on the same body of water. During the refueling procedure, they can easily slow down or even stop for a while.

Therefore, tiny tankers that transport and carry bunker fuel—which is utilized for ship propulsion—are known as bunker ships. While traveling, they can transfer gasoline to a recipient’s vessel. It’s crucial to remember that tankers carrying marine fuel oil for widespread distribution or mass supply at ports are “not” bunker ships. Bunker ships deliver marine fuels or other related fuels, such as lubricants, straight to a vessel.

“Bunkering” is the process of moving these fuels from storage to a ship that is sailing or afloat. Hence, although bunker ships are frequently utilized for midsea fueling, they are also utilized for shore-based or nearby shore fueling, particularly in situations where supplies may be limited. The word “Bunk,” which originates in the Scottish dialect and denotes a reserve or something that is excess, is the source of the names bunker and bunkering.

During the World Wars, when the naval fleet worldwide was actively engaged in maritime warfare or supplied and thus needed to be continuously replenished with fuel for operation and service around the clock, the notion of bunkering was most prevalent for battleships. Furthermore, bunker ships were constructed and widely utilized as short-term reserves to supply boats with gasoline when needed, as many regions of the world were then negatively impacted by an interrupted fuel supply.

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But the idea of “bunkering” also affected other passenger and commercial ships. A recent example of when bunkering became more popular was during the COVID-19 pandemic, when all global supplies—including fuel—were severely disrupted. This, along with the US and many other European countries’ “overconsumption” of fuel reserves—which tended to attend to surplus self-sufficiency in the wake of the plummeting barrel rates and increasing scarcity—left several other maritime nations to look for other temporary respite, like bunkering.

Additionally, even though both countries had comfortable reserve self-sufficiency, they resorted to bunkering their naval vessels amid the ongoing Russian invasion of Ukraine.

Bunker Ships Design

Bunker Ships Design
(Credit: Elenger Marine)

Bunker ships are constructed like tankers, with separate tanks used to hold fuel oils. They frequently feature heating systems on board, particularly in colder regions. Because of their inflammability, which is a constant concern associated with carrying refined petroleum products, extra precautions are necessary to avoid fire outbreaks.

They mostly transport the standard fuels used in ships, such as gasoline, HFO, marine diesel oil, lubricant, and occasionally LNG for ships using it for direct or hybrid power. Their network of pipes is well-designed to facilitate the loading and unloading of gasoline onto other vessels.

Typically, bunker ships are not very big, with tankage capacity ranging from 2000 MT to 10,000 MT for heavier loads. They have two hulls because they are designed like classic tankers. One or two screws could propel them. Hull shapes can vary greatly, but spoon- or chin-shaped bows are typical. Because they transport extremely flammable fuels, tank arrangements are crucial, particularly for ships that transport several types of liquid bunkers that need to be properly separated according to flashpoints.

This technique of sea bunkering is known as “Underway Replenishment” in the naval language. The recipient’s vessel and the supply or bunker vessel may align longitudinally or side-to-side during refueling. The supply vessel can be placed in front of the receiving end or behind it.

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