In This Issue
Transportation Infrastructure
June 1, 2008 Volume 38 Issue 2
Transportation Infrastructure issue of The Bridge, Volume 38, Number 2, Summer 2008

Technological Advances in Maritime Transportation

Wednesday, December 3, 2008

Author: Keith Michel and Peter Noble

The maritime commercial shipping industry has achieved an extremely high level of efficiency.

More than 90 percent of world trade is moved by the maritime commercial shipping industry. Subject to free market forces, this industry has achieved a high level of efficiency, which has contributed to the expanding global economy by enabling the low-cost movement of goods around the world. Worldwide seaborne trade has more than quadrupled in the last 40 years and now exceeds 6 billion tonnes per annum, with an annual growth rate of about 4 percent. Currently some 10,000 shipping companies flying the flags of 150 different countries operate a commercial shipping fleet of roughly 50,000 vessels.

The liberalization of trade in the last few decades has led to specialization among regions around the world. Asian countries have become the leading providers of manufactured goods, for which container ships are the preferred form of transport to overseas markets. In the United States, the demand for petroleum products remains strong while domestic production continues to decline. Thus we can anticipate significant increases in the importation by sea of crude oil and liquefied natural gas (LNG). The growing demand for resources and continuing climate change are expected to create new opportunities for resource exploration, production, and shipping in the Arctic region. More than ever before, the economic and societal well-being of the United States is dependent on efficient, safe, and environmentally friendly deep-sea shipping.


Overview of the Shipping Industry
The merchant fleet consists of a variety of ship types and sizes (Figure 1):

  • Tankers carry liquid cargoes. The world tanker fleet consists of oil tankers (crude-oil tankers and product tankers), chemical carriers, LNG carriers, and liquefied petroleum gas carriers. Tankers vary in size from small coastal vessels to very large and ultra-large crude-oil carriers with cargo capacities in excess of 350,000 cubic meters (m3).
  • Bulk carriers are vessels designed to carry dry cargoes, such as ore and grain, in bulk. These ships range in size up to capsize bulk carriers, which are capable of carrying more than 200,000 tonnes of cargo.
  • Container ships are vessels designed to carry manufactured goods and unitized products in standard-sized freight containers. There are more than 4,000 container ships, ranging in size from small feeder ships to large post-Panamax container ships that can carry more than 12,000 20-foot equivalent containers (TEUs).
  • Other cargo ships and barges include general cargo ships, reefer ships, roll on-roll off (Ro-Ro) vessels, car carriers, forest-product carriers, barge carriers, heavy-lift ships, dry and tank barges, and articulated tug and barge units. Many of these are specialized vessels designed to carry specific types of cargoes.
Remarkable improvements in the efficiency of maritime transportation have been made in the last 50 years. The costs of bulk shipping have increased only about one-tenth of the overall inflation rate, not even double what they were 50 years ago. This translates into lower costs to the consumer. For example, in the United States seaborne transportation adds only about 2 cents to the price of a gallon of gasoline, $10 to the cost of a television, and a few hundred dollars to the cost of a car.

New concepts, such as container ships, LNG carriers, open-hatch forest-product ships, and car carriers have revolutionized the way products are moved. Other improvements have been in the productivity of shipbuilding, the efficiency of hulls and propulsion systems, reductions in manpower requirements through automation, and economies of scale brought about by larger and larger ships.

Comparative efficiencies of transportation modes.
FIGURE 2 - Comparative efficiencies of transportation modes.


As shown in Figure 2, compared to other transportation modes, shipping is a very efficient means of moving cargo over long distances. The high level of efficiency has not only lowered transportation costs, but also significantly reduced greenhouse gas emissions per tonne-mile of cargo moved.

Marine transportation systems have many components that must interact efficiently to provide overall system efficiency. These include ships, marine infrastructure, tugs, navigations aids, search and rescue facilities, salvage and firefighting support, port security systems, pilotage, bunkering facilities, ports and terminal infrastructure, multi-modal interfaces, environmental incident-response systems, and so on. In addition, the U.S. marine transportation system is multifaceted, including ocean-freight transport, Great Lakes and great river navigation and coastal cabotage, and major passenger ferry operations.

Although both domestic and international waterborne transportation are essential elements in the economic life of the United States, this article is focused on three specific sectors that are undergoing particularly rapid change: container shipping, LNG transportation, and Arctic navigation. In all three of these sectors, U.S. designers, shipbuilders, and owner/operators have played key roles in developing technologies that have led to major innovations and successful implementations.

Container Shipping
Container shipping began modestly in 1956 when Malcolm McLean moved 58 containers from New York to Houston. In the late 1950s and 1960s, McLean’s Sea-Land Services and Matson Navigation Company were pioneers in the design of cellular container ships, containers and the means to secure them, container cranes, and other port infrastructure. Within a short time, containerization had revolutionized the transportation industry, and intermodal movements by ship, truck, and rail had become the preferred method of moving manufactured goods and other unitized products.

During the early and mid-1980s, the size of container ships stabilized at about 4,500 TEUs, and the largest container ships had a beam of 32.2 m, the limiting dimension of the Panama Canal. In 1988, America President Lines (APL) took delivery of the first post-Panamax container ship (Figure 1d), which had a beam of 39.4 m and an overall length of about 275 m. Post-Panamax ships are specifically designed for trans-Pacific service. Arranged with a single 41,900 kilowatt (kW) slow-speed diesel directly connected to a single propeller, these vessels are capable of service speeds of more than 24 knots.

The APL post-Panamax design incorporated many innovative features, including lashing bridges for securing on-deck containers, which significantly increased the number of containers that could be carried. Coincident with the introduction of these larger ships, APL developed stack-train technology, which makes it possible to load containers two high on flat railcars. These technological advances provided marked competitive advantages, and in time, post-Panamax container ships became the de facto standard for moving containers in the trans-Pacific and Far East-to-Europe trades.

Although there are diminishing economies of scale for further increases in ship size, the rising price of fuel oil has encouraged the construction of increasingly large container ships. The largest container ships that can transit the Panama Canal have slot capacities up to 5,000 TEUs, but the canal is being enlarged to accommodate container ships of about 12,000 TEUs. The Suez Canal size limit is about 14,000 TEUs, and the Straits of Malacca limit is about 18,000 TEUs.

At this time, the Emma Maersk is the largest container ship, with a length of 398 m, a beam of 56.4 m, and an estimated capacity of more than 12,000 TEUs. Samsung Heavy Industries of Korea is now offering a design with a slot capacity of 16,000 TEUs.

The designers and builders of these mega container ships face many technical challenges. The main deck of a container ship has large hatchways so containers can be efficiently loaded into the holds. This open section leads to significant torsional deformation of the hull girder. Great care must be taken to ensure the watertightness and structural integrity of the hatches and to prevent fatigue cracking at the hatch corners and structural transitions. Sophisticated finite element models are used to evaluate design strength, and loads are developed from linear and nonlinear sea-keeping programs and model tests (Figure 3).


The rating of main engines (Figure 4) that drive mega container ships now approach 100,000 kW, heavy loading for a single propeller. Although twin propellers are an option, single-screw designs are more efficient. Thus the propeller must be designed to deliver high efficiency and maintain adequate structural strength while minimizing cavitation and propeller-induced vibration.

 

Another concern on large vessels is shaft alignment. Computational fluid dynamics (CFD) tools and model testing are used to optimize the propeller design, and finite element analysis is used to evaluate interactions among the hull structure, main engine, shafting, and propeller.


Port infrastructure is being continuously adapted to increases in ship size. Port planning is driven by pressures to increase productivity and throughput and reduce air emissions from the terminal equipment, as well as from the ships, trains, and trucks entering and leaving the port. The ports of Los Angeles and Long Beach, the largest container ports in the United States, have been in the forefront of these changes. For example, new cranes with greater vertical clearance and outreach that require less power are highly automated to improve productivity.

Both ports have embarked on a five-year project to reduce harmful air emissions by nearly 50 percent. This aggressive, multifaceted plan includes financing the replacement or retrofitting of “dirty” diesel trucks that move containers to and from terminals, the acquisition of all-electric cargo-handling vehicles, and the use of pollution-based impact fees to encourage good practices and provide financial support for pollution-mitigation initiatives. Facilities for “cold ironing,” (ships plugging into the port’s power grid rather than using their own diesel-driven generators) have been fitted at many of the berths.

 

Transportation of Liquefied Natural Gas
 

On January 25, 1959, the first ocean cargo of LNG was transported from Louisiana, bound for the United Kingdom, by a small U.S. cargo vessel that had been converted to the world’s first LNG tanker, the M.V. Methane Pioneer (Figure 5). Following delivery of the initial cargo, the ship continued to make periodic deliveries, but the first regular trade in LNG in purpose-built carriers was established between Algeria and the United Kingdom in the mid-1960s. In 1969, Phillips Petroleum (now ConocoPhillips) opened an LNG plant in Kenai, Alaska, and began to export U.S. gas to Japan. Almost 40 years later, this trade is still in place.


LNG cargo is lightweight and cryogenic, with a specific gravity of approximately 0.45 and temperature of −163?C. Because liquid gas slowly boils as it is transported, LNG carriers must have cargo-containment and cargo-handling systems capable of safely handling this cold cargo. Two types of cargo tank systems have been developed: independent tank systems and membrane tank systems.

Independent tank systems have stainless steel or aluminum tanks (both perform well at low temperatures) that are installed into a ship and are supported independently of the main ship structure. The most common independent tank system has spherical tanks that stick up through the deck, giving the ship a distinctive profile (Figure 6).

LNG ship with spherical tanks
FIGURE 6 - LNG ship with spherical tanks. Source: ConocoPhillips. Reprinted with permission.

 

Membrane tank systems have a cryogenic metallic membrane that is installed against the inner hull of a double-hulled ship to protect the ship’s steel from low-temperature effects. Membrane-type LNG carriers have a less distinctive profile, although they are relatively high freeboard ships (Figure 7). These ships require high-volume tanks because of the low specific gravity of LNG (approximately half the specific gravity of oil products).

 

Most new LNG ships have membrane tanks with a typical capacity of about 40,000 m3. Special techniques and equipment are required to manufacture and install membrane tank systems, and only a few shipbuilders, mostly in Korea, are constructing LNG ships. Figure 8 shows a typical membrane tank; the person in the background provides a sense of the enormous size of these tanks.

 

Until a few years ago, the largest LNG carriers had capacities of less than 160,000 m3. However, large gas developments in Qatar led to a major new building program of more than 40 new LNG carriers, ranging in size from the QFlex design (capacity of about 212,000 m3) to the QMax design (capacity of about 266,000 m3). This was a quantum jump in size for an industry that prefers to mitigate risk by making incremental changes. The designs were a collaborative effort of major oil companies and Korean shipyards.

To ensure safety and reliability, extensive design and risk evaluations were carried out during the design process. One of the principal concerns was the development of rational design parameters for scaling up the membrane-containment system. A single tank on a QMax LNG carrier measures about 48 m wide X 28 m high X 58 m long and can hold about 58,000 m3 of LNG, nearly twice the size of the tank shown in Figure 8. A variety of techniques were used to design these tanks, including CFD analysis and tank tests to evaluate the sloshing modes, first-principle structural analysis, and full-scale destructive testing of the membrane elements.

This new generation of LNG carriers has many unique characteristics, such as twin-screw, redundant propulsion and steering systems. The hull form is highly optimized, with a gondola-type stern that directs the flow into the propellers. Whereas most existing LNG carriers burn boil-off gas in steam plants, these ships have highly efficient diesel engines. Instead of burning the boil-off gas, it is re-liquefied and returned to the cargo tanks, enabling the delivery of the full cargo payload to market.

The current trend in LNG propulsion is dual-fuel engines that burn both boil-off gas and fuel oil. Designs are available for both medium-speed diesel engines and slow-speed diesel engines. Gas turbines are also being considered.

Arctic Navigation
For centuries, people searched for navigable routes from Europe to Asia along the Northwest Passage (North America) and the Northern Sea Route (Russia). Today these routes can be navigated, with some difficulty, allowing ships to pass from the Atlantic to the Pacific and vice versa. But experts generally agree that the main use of these northern sea-lanes is likely to remain voyages to specific destinations rather than transpolar voyages; access to Arctic resources and tourism are the main reasons for sailing north.

The Arctic, which is rich in natural resources, has historically provided both biological and mineral resources, such as fishing and whaling (Greenland, Alaska, Canada, and Russia), lead and zinc ore (Greenland, Canada, and Alaska), nickel ore (Russia), iron ore (Canada), coal (Norway), and oil and gas (Alaska, Canada, and Russia).

Global climate change over the past few years has reduced the Arctic Ocean sea-ice cover in the summer months, and some predictions are that the summer ice cover will disappear totally by mid-century. Winter ice cover will, however, remain, although predictions are that the thickness of the ice will decrease some. Nevertheless, navigation will still be challenging.

 

In the United States, major oil, gas, and mineral reserves have already been developed in Arctic Alaska. In the late 1960s, oil was discovered on the North Slope of Alaska near Prudhoe Bay, and production began in 1977. During the development planning for the North Slope, some consideration was given to exporting oil directly from the Arctic to the U.S. east coast via the Northwest Passage, and a specially converted tanker, the SS Manhattan, did in fact make two voyages in 1969 and 1970 to test out this possibility. In the final analysis, however, a pipeline was built across Alaska, and the crude oil was transported to the U.S. west coast in purpose-built tankers (Figure 9).

In parallel with oil and gas development, there has been some significant mining development in Alaska. In 1989, the largest zinc/lead mine in the world, the Red Dog Mine, started production about 80 miles north of Kotzebue. Today this mine produces about 600,000 tonnes of zinc concentrate per annum and about 100,000 tonnes of lead concentrate per annum.

The ore is stockpiled throughout the winter and exported by ship during the short summer open-water season. Because of the very shallow water near shore, which is typical of the U.S. Arctic, and the total absence of ports and other marine infrastructure, the mine has built a marine terminal for loading shallow-water barges with ore concentrate. Barges carry the ore from the terminal to bulk carriers anchored in deeper water, and the cargo is trans-shipped at sea.

Recent oil and gas lease sales by the U.S. government drew record-high bids. In February 2008, more than $2.5 billion was put up for leases in the Chukchi Sea. Development of these sites will require special marine assets, including drilling rigs, ships, semi-submersible or jack-up units, and supporting resupply and ice-management vessels. Similar arctic offshore explora-tion was successfully carried out in the Canadian Beaufort Sea in the early 1980s, and current and future exploration will build on that experience.

To date, development in the U.S. Arctic offshore has been mostly in very shallow water in the Prudhoe Bay area and has relied on traditional pipeline export systems to connect to the trans-Alaska pipeline. In the future, oil and gas discoveries in the Arctic may very well be in deeper water and farther from land, which will involve major shipping activities.

 

ConocoPhillips, with its Russian partner LukOil, is currently developing an arctic crude-oil export system that may be a prototype for the future. The system consists of a pipeline from short-term storage tanks to a fixed, offshore, ice-resistant off-take terminal (Figure 10), and three purpose-built ice-breaking oil tankers equipped with diesel electric propulsion and azimuthing electric drives (Figure 11). These tankers will shuttle oil out of the ice zone to Murmansk, where it will be trans-shipped into open-water tankers for delivery to markets in Europe and North America. In addition, two ice-breaking support vessels are being built to support activities around the terminal during loading (Figure 12).

 

The Changing Environment and Future Ship Design
Public expectations for improved safety and environmental performance will have a major influence on ship design in the next decade. Although oil spillage from ships has significantly decreased in the past 30 years, further reductions are expected by a concerned public.

International regulations now require that bunker tanks on new ships be double-hulled or provided with equivalent protection. Thus newly built ships can no longer carry fuel oil in wing tanks outboard of the cargo holds to maximize carrying capacity. To minimize the negative impacts of these changes on efficiency and capacity, new designs are being developed that allocate fuel in protected locations in superstructures and between holds.

Another environmental concern is the introduction of non-indigenous species from ballast water. Currently, ballast water is exchanged in the open ocean, and ballast-water treatment systems are used to reduce the likelihood of introducing invasive species. Eliminating ballast-water discharge completely is the failsafe solution. This is a practical option for large container ships and Ro-Ro vessels, which generally move cargo on every leg of the voyage. However, it would not be practical for tankers and LNG carriers, which typically deliver their cargo and return empty. A few recently built ships have internal freshwater ballast-transfer systems (for example, the Ro-Ro shown in Figure 1a), which not only enable the control of the vessel’s trim and heel but also eliminate the need for saltwater ballast with its corrosion-inducing properties.

The large diesel engines on oceangoing ships are well suited for burning residual oils, and the lower cost of heavy fuel oil (compared to the cost of distillates) has contributed to the efficiency of the marine transportation system. Unfortunately, because of the high sulfur content of residual oils, shipping is a major emitter of sulfur oxides (SOx), and pressure to reduce emissions of SOx, nitrogen oxides, and particulate matter is increasing. Full-scale tests are being conducted on various pre-treatment (e.g., water emulsion) and post-treatment (e.g., scrubbers and selective catalytic reduction) systems.

International regulations now under consideration will require that ships burn increasingly cleaner fuels. By 2020, it is likely that ships will only be permitted to burn low-sulfur diesel oil or marine-gas oil or to install treatment technologies that reduce emissions to equivalent levels. The shift toward these higher cost distillates, as well as the dramatic rise in fuel prices, will encourage further efforts to improve the efficiencies of the hull and propulsion systems.

Significant fuel savings can be realized by reducing ship speed, which would decrease wave-making resistance, which is magnified at higher speeds. With the rise in fuel costs, the optimal service speed for minimizing freight rates is now much lower than the typical container ship speed of 22–25 knots, LNG ship speed of 19–21 knots, and oil tanker speed of 14–16 knots. Market willingness to pay for faster delivery will surely be tested in the coming years.

In this rapidly changing environment, adaptability will be the key to success. Although U.S. shipyards are no longer internationally competitive in the labor-intensive business of shipbuilding, U.S. owners and designers will have significant influence on future ship designs. In the coming years, naval architects and marine engineers will have ample opportunity to explore creative options, because new markets such as mineral and petroleum production in the Arctic will require innovative concepts and techniques. In addition, existing markets will require continuous improvements in efficiency, safety, and environmental performance.

Multi-purpose icebreaking supply vessel
FIGURE 12 - Multi-purpose icebreaking supply vessel. Source: ConocoPhillips. Reprinted with permission.

Arctic Ice breaking tanker
FIGURE 11 - Arctic Ice breaking tanker. Source: ConocoPhillips. Reprinted with permission.

Fixed offshore ice-resistent offtake structure
FIGURE 10 - Fixed offshore ice-resistent offtake structure. Source: ConocoPhillips. Reprinted with permission.

Double hulled, twin screw tanker
FIGURE 9 - Double hulled, twin screw tanker. Source: ConocoPhillips. Reprinted with permission.

Main cargo tank of an LNG ship
FIGURE 8 - Main cargo tank of an LNG ship. Source: ConocoPhillips. Reprinted with permission.

Typical LNG ship with membrane tanks
FIGURE 7 - Typical LNG ship with membrane tanks. Source: ConocoPhillips. Reprinted with permission.

The M.V. Methane Pioneer at a loading berth in Louisiana
FIGURE 5 - The M.V. Methane Pioneer at a loading berth in Louisiana. Source: ConocoPhillips. Reprinted with permission.

A MAN B&W 12K98ME diesel engine (68,000 kW)
FIGURE 4 - A MAN B&W 12K98ME diesel engine (68,000 kW). Source: MAN Diesel. Reprinted with permission.

Test of a container ship model in extreme head seas.
FIGURE 3 - Test of a container ship model in extreme head seas. Source: American President Lines. Reprinted with permission.

Types of ships in the merchant fleet.
FIGURE 1 - Types of ships in the merchant fleet. 1a. Roll on-roll off (Ro-Ro) vessel. 1b. Bulk carrier. 1c. Crude-oil tanker. 1d. Container ship. Sources: Totem Ocean Trailer Express Inc.; EastWind Maritime; General Dynamics NASSCO and BP Shipping; American President Lines. All photos reprinted with permission.

About the Author:Keith Michel is chairman of Herbert Engineering Corporation. Peter Noble is chief naval architect at ConocoPhillips.