Exhaust Emissions and the Cruise Ship Industry

Toward the end of May, environmentalists arrived at the cruise ship terminal at New York City to protest exhaust emissions from cruise ship engines. Specifically, the protest was directed against cruise ship operators that were burning heavy fuel oil in their engines, courtesy of the American administration that has been more flexible that the European Community in terms of ship engine emissions. 

Until a decade ago, while transportation departments internationally imposed increasingly stringent standards on road vehicle exhaust emissions, they paid little attention to ship exhaust emissions. In recent years, the European Community initiated policy action to require cleaner exhaust emissions from large ships, including the use of exhaust scrubbers. In the U.S., environmentalists have expressed concern over cruise ships that the Alaska service using heavy fuel oil that increases output of black carbon in the exhaust emissions and especially from ships that sail into the Arctic region, where they believe black carbon to increase Arctic melting.

Carnival Cruises and their subsidiary ship companies represent a significant proportion of the cruise ship industry. While burning heavy fuel oil on some of their ships, their fleet currently includes two ships that while tied up in port, burn LNG. Later this year, they will introduce to the cruise market their first LNG powered ship that will burn LNG while at sea and have several additional LNG powered ships under construction. They advised that they have installed exhaust gas cleaning technology across 60 percent of their fleet, with cleaner emissions than non-modified ships burning low-sulfur fuel.

A small percentage of the cruise ship market seeks to travel aboard wind-driven vessels. Between 1987 and 2002, Carnival operated a four-mast schooner/yacht that could sail either on wind power or diesel fuel. An engine fire in 2002 led to the vessel being scrapped. Several other cruise ship operators own sail-powered passenger vessels with one company operating a cruise vessel that includes a kite to provide towing from more powerful winds that blow at higher elevation. Various designs of wind turbines have been tested for boat propulsion and have been applied to cargo transportation.

The diesel engine industry has made major strides in improving engine efficiency and reduce exhaust emissions. Computer controlled electric solenoids now drive fast acting fuel injectors with variable timing capability that have replaced slower operating mechanical fuel injection systems, and electrically driven solenoids instead of mechanical mechanisms now activate engine valves. Presently, the cruise ship industry is in the process of replacing older less efficient engines with newer more efficient engines that emit fewer pollutants.

Emissions Free Cruise Vessels

While the environmental movement supports the operation of emissions free tourist ships, there may be limited short-term application for such technology. It may be possible to convert river cruise boats to battery electric propulsion due to the ability to rapidly recharge graphene-based batteries at navigation locks. These batteries are still under development. Wave powered vessels sail at speeds of six to eight knots, in optimal wave conditions.

In tropical regions, surface seawater is warm while water deep down is barely above the freezing point. Proven technology can generate propulsive energy from the temperature difference, with a vessel of 500 passengers sailing at six to eight knots. Long-life thermal batteries based on heat-of-fusion technology could provide sufficient energy to propel a ship for up to 750 nautical miles and would need to recharge overnight from a coastal thermal power station. The main problem with battery propulsion is the amount of physical space it requires as well as the weight that would reduce payload capacity.

Tug Barge Option

One alternative to the weight and volume requirements of batteries would be to build cruise ships as barges to be pushed by ocean capable battery tugs. Such technology could be adapted to the river and inland waterway cruise industry, except that vessels would spend longer times at navigation locks to transit both barge and tug. Tugs pushing and navigating cruise ship size barges operate on North America’s Upper Great Lakes as well as along the American coast with waves of 20 feet (six meters), involving bulk carrier barges built to lengths of 600 feet to 875 feet. 

The large North American tug barges are proven technology that could serve as the basis to develop cruise ship tug barges that could sail around the Caribbean and Mediterranean regions. In port terminals, the super tugs would be uncoupled and at some brief stop overs at ports-of-call where tugs could be exchanged for a freshly recharged unit, while the exhausted unit undergoes a recharge after some 800 nautical miles of service. At the main terminal, the super tug would be coupled upon departure and uncoupled upon arrival. During at-sea emergencies involving propulsion system malfunctions, tugs could be exchanged.

Towed Electric Power

While bi-directional rotation diesel engines directly drive propellers on the majority of freight ships, most cruise ships use diesel electric propulsion, and most onboard cruise ship operations depend on electric power. It is technically possible for a cruise ship to tow a twin-hull catamaran floating electric power unit that includes electric power cables that connect directly into ship operations, including propulsion. The floating towed unit could carry any of a massive array of grid-scale chemical batteries, thermal energy storage that produced electric power, an LNG gas turbine generator or even a micro-nuclear electric generating technology.

While the towed electric unit increases available space aboard the ship, it can be designed to include some autonomous capability that includes hydrofoils. When one towed unit malfunctions, a stand-by unit could be rapidly dispatched from shore and ride on hydrofoils to assure faster arrival time. Popular tourist regions where such technology could operate include the Caribbean and Mediterranean areas. When at the main port terminal, the towed power unit would be uncoupled with shore based power sustaining hotel power, with onboard batteries providing short term power when leaving port and when arriving.

Conclusions

While some segments of the cruise ship industry still burn heavy oil, the industry is in the process of replacing some of the older engines with newer and more efficient engines that burn newer diesel formulations that deliver cleaner exhausts. However, the process will take several years. Zero emissions cruise vessels are possible, and in the near term future, will operate in specialized markets such as river cruises and windswept regions of the world where wind powered or wave powered propulsion is possible.