PORTLAND – The international ferry Scotia Prince is expected to be back in Portland next spring after undergoing a cleaning and refurbishing over the winter in South Carolina.

The 485-foot ferry saw its business decline last season, raising some doubts about its future. But Mark Hudson, vice president for finance and communications for Scotia Prince Cruises, said Wednesday that the vessel will resume its runs in May between Portland and Yarmouth, Nova Scotia.

While in a Charleston, S.C., dry dock, the ship will be lifted out of the water and have its bottom cleaned. Workers also plan to complete the installation of an $800,000 sprinkler system to ensure that the ship meets safety standards.

The Scotia Prince, which goes into dry dock every two years for routine maintenance, has been asked by the city to leave its terminal in order to accommodate a new cargo ship that will restart container traffic in and out of Portland Harbor.

Jeff Monroe, Portland’s director of ports and transportation, said the cargo ship is expected to arrive by the end of the month. It will make a weekly visit to the International Marine Terminal.

During the past summer, the Scotia Prince experienced a sharp drop in ridership. At the end of the season in October, Hudson calculated that passenger totals were down 23 percent from 2003 and 30 percent from 2002.

He blames mold and other problems at the International Marine Terminal, which is owned by the city of Portland, for some of the reduction in passengers.

“The season started low and then the revenues and sales were really picking up,” he said. Then mold was discovered in the terminal in August and the company pulled its employees out of the terminal and processed passengers in a tent outside.

“The mold problems at the terminal really dramatically affected the sales,” Hudson said. “They dropped off very quickly.”

Monroe said mold remediation work will soon be completed and the terminal will be ready for the Scotia Prince in the spring. Plans call for the ship to move into the new Ocean Gateway terminal at the eastern end of the waterfront, which is expected to open in 2006.