S5C4: Cargo Ships & Submarines

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a) The containerization of freight

Long gone are the days of sailing ships, then steamers, carrying passengers and goods across the oceans over long voyages. The voyages are still quite long but the plane has taken over for passenger transport, outside of the niche case of cruise ships that often start and end in the same place anyways, and the shape, size and powering of cargo ships has undergone a radical transformation involving more specialization. In the age of the containers, this statement deserves some clarification.

Containers are not ships, they wrap around goods that need to be transported so that all those goods now can be handled and transported in a standardized manner. Containers enable the treating of non-commoditized products as commodities with the caveat that each box is identified so ownership and intended destination can be tracked. Essentially, a container abstracts its content and reshapes it as a rectangular-shaped box with fixed dimensions of 20 feet or 40 feet in length (6.1m or 12.2m), 4.4m wide and 2.6 or 2.9m in height. Thus, the carrying capacity of a container ship is expressed in twenty-foot equivalent units (TEU).

This has been transformative for non-bulk cargo ships and equally so for ports’ infrastructure, equipment and productivity, as we will see in the upcoming Chapter 8 on ports and airports. The latest generation of container ships measures around 400m in length and can carry up to 24,000 TEU, which is more than 15 times the capacity of large pre-WW2 cargo ships. One cannot see it from the outside but the containers are not positioned on a flat deck, this would be not merely a waste of space but it would also make for a high centre of gravity and therefore less stability as compared to having weight as close to the waterline as possible. Therefore, containers are laid straight into the hold, separated into cells by vertical walls every now and then – of course these bays have step-like structures immediately against the hull to provide a horizontal and stable footing for the containers. No hatches involved, it is all open air, and the containers are lined next to each other and then stacked up pretty high with some lashing to prevent too many of them being dropped into the sea in high-wave conditions. The coordinates system works as follows: bay number starting from the front, row number across the ship starting from the centre and then alternating odd and even number at starboard and port side respectively, and the tier corresponds to the vertical level starting from the bottom.

Speed is not paramount for this type of ship, especially since goods requiring express logistics can be air-freighted, though the more trips a ship can make in a given year, the more revenues it can generate for its owner, hence the average cruising speed is still a rather sustained 20 knots or thereabout (around 35km/h). The technology of choice to propel these giants of the sea, and it is the same for the super large bulk carriers and tankers, is two-stroke diesel engines. We have seen two-stroke and diesel in S5 Section 2.b and the key difference is the size of the engines and pistons. For example, the Emma Maersk is equipped with a 2,300t engine with maximum power output in excess of 100,000hp at 102 rpm, that is the same as 600 mid-sized cars, and generates a stunning torque of 7.6 million N.m, which is a lot more of those cars.

The chemical reactant of choice for these engines is heavy fuel oil, also known as bunker fuel, because it is significantly cheaper. Not exactly the cleanest of petroleum distillates unfortunately, although some noticeable improvements have been made in reducing noxious content such as sulphur and the emission of particulate matter into the oceans. Could do with some kite lifting here (refer to S5 Section 2.e to understand this allusion). In an aqueous environment, the rotating crankshaft doesn’t drive wheels in contact with a road or rail, instead it drives the rotation of a propeller along a roughly horizontal axis. The screw-like shape of the blades pushes some water towards the back, creating a lower pressure zone immediately ahead of the blade and a higher-pressure zone behind, effectively causing the motion of the propeller forward, and that of the ship with it. This is analogous to the wind moving gaseous molecules from areas of high pressure to those with lower pressure.

Another important factor in the success of containerization, and this goes hand in hand with the commoditized aspect of the goods shaped in the form of metal boxes, is that any container ship is as good as any other, just like buses, or trains for passengers. This means boxes can be laid on the next available container ship and the container ship doesn’t have to wait for specific cargo; it can just pick up what is available, subject to the final destination. And even this is a somewhat flexible variable because, like classification yards for trains or airport hubs for aircraft, trans-shipment is relatively easy to carry out in modern harbours. Not ship-to-ship but ship-to-storage yard and then back onto another ship heading to the intended final destination this time. Accordingly, it is possible to drive efficiencies with many operators setting fixed line schedules so that producers or sellers have the option to time their logistics based on this and the assurance of some trips taking place over several months or even years is an important aspect in the development of robust supply chains.

b) Moving commodities

There are certainly more than three types of cargo ships plying our oceans and rivers though the vast majority of the tonnage is moved by one of three types: the container ships we saw in the previous section and the bulk carriers that can be sub-divided into dry bulk and tankers carrying liquid commodities such as crude oil.

Dry bulk carriers primarily carry raw materials, from the port situated closest to the mine (it would have been trucked or brought by train there) and up to smelters or other types of processing centres, and in the case of thermal coal, to power plants as well. This creates a significant asymmetry in the journey involved as bulk carriers quite often will return empty since the production and processing centres are rigidly set and are far from evenly distributed. Case in point: Brazil and Australia are exporters of iron ore or Indonesia of thermal coal with a lot of the flow going towards Northeast Asia (China, Japan and South Korea) and nothing much to pick up by way of raw materials there to fill the cargo ships on the way back. By the way, one should think of bulk as an unpackaged cargo, so it only works with commodity, where one part of the cargo is as valuable as another. To provide some flexibility and also for safety reasons, the cargo space is split into different holds that can transport different products without them commingling.

Generally, the larger the ship, the more economical the transport but with size and tonnage come some constraints such as width and draft (the vertical clearance required by a ship measured from the waterline so that the keel doesn’t ram into an obstacle). These parameters engender a classification of bulk carriers into six major types starting with “small” all the way to “very large” with that last term only being applicable for tankers. Above small are Handysize and Handymax classes with carrying capacity of up to 60,000 dead weight tons (DWT) and length of up to 200m, then we have Panamax with a max length of 290m, width of 32m and draft of 12m so those were allowed to navigate the Panama Canal (we will take a look at this well-known piece of infrastructure in section g) even before the third set of locks was opened a decade ago. And just below very large is Capesize, too large for the Panama and Suez canals so they have to go the long way around the Cape Horn at the tip of South America and the Cape Agulhas at the southern end of Africa (and farther south than the nearby but better-known Cape of Good Hope). It is worth noting that this classification for international routes is mirrored with other class names and dimensions for regional trades, depending on specific natural features and infrastructure limitations. For example, Seawaymax refers to the largest vessel that can fit through the locks of the St Lawrence Seaway between Lake Ontario and the Gulf of St. Lawrence opening into the Atlantic Ocean.

One of the two main differences between dry bulk carriers and tankers has to do with the loading and unloading of cargo because liquids offer the option of pumping content in and out of the ship through pipes, a much more effective way than using cranes and buckets, however large those are. The second key difference has to do with the effect of a leakage because the products transported by tankers can wreak havoc with ecosystems over a wide area and for many years if a large spill takes place. Following such disasters, the construction of single-hull tankers has been phased out and double-hull is now the norm.

Most of the products carried by tankers, and certainly the larger ones, is either chemicals or hydrocarbons. This includes unrefined oil called crude oil, refined petroleum products and petrochemicals, liquefied petroleum gas and more recently liquid natural gas (LNG), being mostly methane (CH₄) cooled down to -162°C, which is the phase transition threshold from gas into liquid at a pressure of 1 atm.

The largest of the ships, the very large crude carriers (VLCCs), can carry up to 2 million barrels (this is about 318 million litres and for heavy crude this would be about 320kt of cargo). Although it is quite uncommon, there are also some ultra large crude carriers that can transport up to 3 million barrels of crude. These are relatively low-technology ships, not so for LNG carriers given the critical aspect of cooling the fuel and maintaining it at this low temperature throughout the journey. The largest carriers can transport in excess of 250,000 m³ of LNG, which would translate into more than 150 million m³ of natural gas. These particular models use membrane storage but the more common sight is spherical tanks because they are more robust and optimize the surface-to-volume area, thus minimizing heat transfer, but they obviously do not fit neatly into the hull.

c) Ferries

Much more human-sized and trafficking in people as well as cargo are ferries. These can be quite small when fully dedicated to passengers over calm bodies of water or much larger to face the open seas and carry vehicles, equipment and food. If you do not live in an area serviced by ferries, it is easy to underestimate the importance of this mode of transport but, in archipelagos such as those of Indonesia and the Philippines, they provide vital economic links. They can also be used in places, such as the Norwegian fjords, where building bridges would be either uneconomical, unsightly or could have damaging effects on the local ecosystem. Another iconic place of operation is along the western coast of Canada and all the way to the Aleutian Islands, at the western end of Alaska. This is the domain of the Alaska Marine Highway System which goes as far south as Bellingham, near Seattle in the contiguous United States. And of course, the primordial ferryman was Charon, transporting souls across the River Styx and into the underworld of Greek mythology.

When carrying vehicles, these ferries are nicknamed ro-ro, which stands for roll-on/roll-off. It works like a moving piece of road: drive across a ramp onto the ship, park, and drive out when the ship has reached. These can be quite big and plying the route between Dublin (Ireland) and Holyhead (Northeast Wales) is a colossus named Ulysses which can carry up to 1,342 car-equivalent over its 4,101 lane meters of cargo. For long distance crossings, in addition to passenger seats, the ship can be outfitted with cabins, though not always with beds… nothing like sharing a mat overnight with strangers.

d) Maritime routes and chokepoints

Historically, land caravans had optionality in terms of routes between their point of departure and destination, though they were still beholden to topographical barriers such as mountain ranges and other practical aspects, in particular the necessity to resupply their food and freshwater reserves. This made certain oasis and specific locations must-go through zones, with associated risks and levies.

Maritime transport likewise can adopt different routes on the open seas and yet, there are natural bottlenecks, physical chokepoints for trade that can quickly escalate to become geopolitical flashpoints. In the days of the Mediterranean trade, the Straits of Gibraltar would have been the epitome of the chokepoint but there were also immense strategic advantages in taking and retaining control of places like Carthage/Tunis, Malta and Sicily. Later on, the British Empire would exert control over the Atlantic-to-Northern Europe trade moving through the English Channel and the Russian Empire always sought to establish a warm-water access for its merchant and military fleets from the Black Sea to the Mediterranean Sea by way of the Bosphorus Straits and the Dardanelles.

Nowadays, those chokepoints have to do with the flow of energy. We have already looked at this aspect when considering pipelines in S5 Section 1.f and here we will run through the five main strategic bottlenecks the maritime trade is exposed to, going from East to West on a Mercator projection world map, from one side of the Bering Strait to the other.

The Straits of Malacca have always been important in the Europe-to-Asia maritime trade. They are 900km long and as narrow as 65km between Sumatra and the Malaysian Peninsula. Through it, crude oil from the Middle East and Africa makes its way to the Singapore refineries, Vietnam and the large economies of Northeast Asia. That’s about 20 million barrels per day, not counting the LNG coming from Qatar. Thanks to increased multi-national cooperation in the region, the incidence of armed robberies has decreased from the levels seen during the 1990s and 2000s.
Almost an equivalent amount of oil plus the Qatari LNG goes through the Straits of Hormuz, that is about a third of the total LNG produced globally. Hormuz is an island situated to the south of Bandar Abbas in Iran and across the water from Oman and the UAE. This means it is the only way out for ships loading petrol and LNG in the Persian Gulf – think Kuwait, Iraq, Iran, Abu Dhabi, Qatar, and the northeast coast of Saudi Arabia, the one closest to the giant Ghawar oilfield. Here the risk is completely political with Iran holding a potential lever to exert pressure on countries it is doctrinally and politically confronting.
Piracy is somewhat under control in the Far East but still very much a problem in the Gulf of Aden, between Yemen, Djibouti and Somalia, as well as along the coast of Somalia, the Horn of Africa. The risk here is much less politically motivated and piracy is a profession with ransoms the main source of revenues. This illegal activity is so rife that insuring cargos and crews has become very expensive and military escorts are sometimes called upon.
The Suez Canal links up the Red Sea to the Mediterranean Sea through Egyptian territory, in close proximity to Israel, Jordan and Saudi Arabia. The nationalisation of the canal in 1956 triggered the Suez crisis; I include the link to the Wikipedia entry for this event at the end of this chapter. About 12% of global trade goes through this waterway, which includes a lot of container ships bringing Asian manufactured goods exported to Europe and the US East Coast. Depending on the point of origin of the cargo, the distance savings vary from 6,000 km at the bottom end to much more when coming from the Persian Gulf or heading into a port situated in the Mediterranean Sea.
For the Panama Canal, the distance savings range from 3,700km on a Europe to East Asia route and 6,500km from the East to the West coast of the USA. The canal goes through the namesake country and therefore enables ships to completely avoid going around South America, a long and arduous voyage considering the harsh seas near the Tierra de Fuego. Originally under US ownership and then handed over to the sovereign country of Panama in 1974, there has not been acute tension so far. However control of ports and assets in the area by China and the importance the waterway has for the trade of both China and the USA, make this an increasingly strategic location in the new cold war developing between the two competing powers. We will look at both this and the Suez Canal from a technical perspective in section g).

e) Technology under the sea

A submarine is a boat capable of being submerged and it does so by being negatively buoyant, meaning its weight is more than that of the water it displaces. However, it also needs to be able to make its way back to the surface, eventually, to change crew and resupply in food and possibly in fuel. For this, the craft needs to become positively buoyant. To alter buoyancy, submarines use ballast tanks that get filled with water to shift the submarine into negative buoyancy and filled with air kept in reserve in compressed form to go into ascent mode. Want to go down again? Just let the air escape and the ocean water back in the ballast tanks.

In reality, the process is not as intensive as it sounds in terms of air volume because the submarine is kept close to neutrally buoyant and most of the ascent or descent velocity is provided by the tilting of the U-boat by moving the air and water across the connecting tanks, by the various planes acting like sails to provide upward or downward lift, and by the propeller at the tail end. Most submarines are, like ships, fuelled with diesel (or diesel-electric) but military versions might be powered by small nuclear reactors permitting high cruising speeds and week or months-long surface intervals.

What about the oxygen and carbon dioxide content in the air though, how are these maintained over such long periods? As usual, nothing a little engineering and chemistry can’t solve. Oxygen is obtained from water (and there is plenty around a submarine) by electrolysis and the carbon dioxide can be “scrubbed away” through chemical reaction. For fresh water, the saltwater goes through reverse osmosis (we will explore this technology in S5 Section 9.d) to obtain purified water needed for cooking and potentially for operating the nuclear reactor.

In order to sense its surroundings and orientate itself, at or near the surface the craft can use GPS or radio for positioning and a periscope for visual sightings. At depth however, these methods are not available so dead-reckoning will be used thanks to equipment such as a gyrocompass and speed sensors as well as an inertial navigation system detecting positive and negative deceleration as well as pitch and roll – you may want to refer to S4 Section 9.c on the gyroscope and accelerometer to better understand these terms and sensing technologies. When not trying to go undetected, a U-boat can also rely on sonars that project underwater sound waves to map their surrounding through their echoes.

Civilian submarines are primarily used for scientific, repair and salvaging purposes but the military ones would come equipped with weapons such as torpedoes or missiles. Both are self-propelled and a torpedo operates underwater with the objective to breach hulls and sink ships whereas a missile would have targets at the surface or in the air. This means the torpedo tubes would be positioned horizontally in the submarine and the missiles would exit vertically, up through the water, and fire their rocket engine after breaching the surface.

f) The strategic submarine

The ability of submarines to avoid visual and even radar detection enables them to get around traditional geographic chokepoints as well as approach targets undetected. One way to think about it is that they do not play by the same rules, they cheat as far as traditional maritime military power is concerned.

The advantage is not merely tactical, during active warfare and engagement, it is also strategic through the potential impact over supply lines in case of a conflict or the threat presented by one armed with nuclear warheads. This military craft came into its own during the First World War with Germany attacking merchant and passenger ships plying the Atlantic, mostly between the USA and the UK. The British Royal Navy also suffered significant losses. Furthermore, submarines can be used not merely to attack ships but also to lay mines in the vicinity of harbours and, with modern technologies, they can launch missiles aimed at air and land targets, including both civilian infrastructure and military equipment.

During WW2, the USA turned the tables with their submarines destroying more than 1,000 ships in the Pacific Theatre, more than half the total loss of warship suffered by the entire Axis powers of Germany, Italy and Japan combined. Furthermore, they can be used to defend aircraft carriers and to carry out intelligence and special force assignments.

The installation of nuclear warheads has changed the nature of the game though and, from active threat, submarines have come to instantiate the Damocles sword represented by nuclear deterrence. Indeed, they represent launch locations that are difficult to detect and destroy because they are mobile and can reach any target in stealth mode. And it doesn’t take many of them to make the threat more than hypothetical.

g) Trivia – the Suez and Panama Canals

There had been early versions of the Suez Canal during the time of the Pharaohs, more than two millennia ago, nevertheless those only linked the Nile to the Red Sea and it took 10 years, throughout the 1860s, to cut through the mostly flat land with the benefit of the Great Bitter Lake on the way. The canal was initially operated by a concessionary company with mostly French and British shareholders until the nationalization of 1956.

The Suez Canal measures 193km in length and is 205m wide with a maximum allowed boat beam (width) of 77m and an allowed draft of 20m. The topography is such that there is no lock involved and only a minor difference in sea level between both ends. Thanks to the construction of a new section concluded in 2015, the canal can accommodate traffic in both directions simultaneously along that stretch and unidirectional convoys departing at fixed times each day can now go past each other in the central two-lane section.

The Panama Canal is a slightly more complex affair in terms of topography and locks. It bisects the Isthmus of Panama in the northwest to southeast direction, linking the Caribbean Sea near Colon to the Pacific Ocean near Panama City. There as well, navigation occurs across an existing lake for a substantial part of the waterway which happens to be 26m above sea level, hence the need for several locks to bring the ships up and back down. The canal’s total length is 82km, including the lake section, with maximum draft of 15m and maximum beam of 51m (it was 33m until the new set of locks completed in 2016 and then 49m until mid-2018).

There are a total of six pairs of locks, a 3-step flight at Gatun to get to Gatun Lake and then 1 step at Pedro Miguel followed by 2 steps at Miraflores to make it into the Pacific. The pair system is designed to allow ships to pass through in opposite directions simultaneously although turns need to be taken to go through the Culebra Cut so in reality the locks are often used in one direction and then in the other one, by batches.

The infrastructure project was completed by the USA in 1914 (it was started by France in 1881 and then stopped for 15 years due to lack of funding) and handed over to the Panamanian government in 1999.