PORTLAND – Large ferries such as The Cat and the Scotia Prince could be attractive targets for terrorists, says the Coast Guard, which is looking at ways to beef up security.

After five months of study of how to blow up large ferries, the Coast Guard is working with industry officials to help come up with security measures that would not interfere with the flow of passengers.

The Coast Guard is focusing on ferries that carry more than 2,000 passengers or more than 500 passengers plus vehicles.

The Cat and the Scotia Prince, which run between Maine and Nova Scotia, both fall in that category, although the Scotia Prince recently said it will not be sailing this season because of a mold problem at its Portland terminal.

The Coast Guard study was prompted by a terrorist attack against a large ferry in the Philippines last year that killed more than 100 people, said Jolie Shifflet, a Coast Guard spokeswoman in Washington.

“While we don’t have information that indicates a specific threat to the ferries, we do have information that shows this would be an attractive target,” Shifflet said.

“We recognize there is a potential for a significant loss of life on a ferry because of their size and because sometimes they are transiting very cold water,” which would reduce passengers’ chances of surviving an attack, she said.

All ferries have had to meet a set of security criteria since July, including the relatively small ferries that serve islands in Casco Bay. Those measures include monitoring the ships and landing facilities with either live patrols or security cameras.

The latest study aims to develop additional standards for larger ferries. The study is classified, but some ferry industry personnel have been given classified security clearance so they can give feedback on the study results and whether additional security steps are warranted.

The study included structural analyses of different types of ferries and computer models of what would happen if bombs of different sizes were set off at different locations in a vessel, Shifflet said.

“Knowing the amount of explosives it will take to sink the ferry will help determine the appropriate screening measures,” she said.

Ferry operators accept the analysis as part of business after the attacks of Sept. 11, 2001.