Not surprisingly, fuel makes up a significant portion of a cruise ship’s operating budget – about $1 million for a 10 day trip – but due to tighter maritime industry emissions regulations, these costs are sharply rising.

Cruise ships are often described as floating hotels, but they are also floating power plants. “This ship is a diesel-electric plant,” Richard Pruitt, Associate Vice President of Safety and Environmental Stewardship at Royal Caribbean recently told a group of journalists during a tour of the “Explorer of the Seas,” at the Cape Liberty Cruise Port in Beyonne, New Jersey.

The ship is powered by 6 V12 diesel engines made in Finland by Wartsila that are connected to 6 12.6 MW electrical generators manufactured by Swiss company ABB. The ship was “bunkering” or taking on 1,300 tons of fuel during the tour. The Explorer holds two types of marine fuel because US and international law dictate that low sulfur fuel oil must be burned within 200 nautical miles of member-country shorelines, a boundary known as the Emissions Control Area established by the International Maritime Organization.

“IMO – the International Maritime Organization – is the United Nations specialized agency with responsibility for the safety and security of shipping and the prevention of marine pollution by ships,” according to organization’s website.

New air pollution regulations took effect in August, 2012 that impact cruise ships, and Royal Caribbean “had problems getting compliant fuel in the Pacific Northwest,” Pruitt told Breaking Energy. Dealing with the emissions issue is currently his greatest challenge, he said.

The IMO regulations specifically concern sulfur content, but sulfur is only one of many specifications that need to be met for a ship’s engines to run safely and efficiently. The low sulfur fuel grade offered by a regional supplier may not meet the specifications required by the engine configuration on a given class of ships.

Additionally, space comes at a premium on ships and the need to carry multiple grades of fuel means multiple tanks must compete for precious square feet.

Pruitt thinks the solution could lie in scrubbers, much like those used by utilities operating coal-fired power plants. He said two ships experimenting with them now “show great promise.”

But the regulations are scheduled to tighten even more from less than 1% sulfur fuel now to below 0.1%, which could double fuel costs inside the ECA, according to Pruitt. Scrubbers will likely be required to some extent, he said, because the sulfur content of fuel can only be reduced so much. In order to comply with regulations, some contaminants may need to be scrubbed out after the fuel is burned.

The dilemma is similar to that faced by utilities up against expensive retrofits needed to bring their fleets of coal-fired power plants within compliance. The difference is that utilities have been able to switch to cleaner burning – and currently cheaper – natural gas, while shipping interests don’t have that luxury.