BOSTON (AP) — They're not castaways, but like the tourists on television's Gilligan's Island, a group of whale watchers expected only a three-hour tour but got much more after their boat was snagged by a lobster trap rope outside Boston.

Boston Harbor Cruises passenger Ken Maguire said they expected to be back Monday around 4:30 p.m. but about 10 minutes into the return trip their boat stopped after apparently hitting something.

Coast Guard Petty Officer MyeongHi Clegg said the boat's propeller became entangled in a lobster trap rope about 15 miles offshore. She said the cruise company couldn't remove the rope and plans to transfer the 157 passengers and six crew members to another vessel didn't pan out. Everyone will stay aboard the boat until sometime Tuesday morning.

Clegg said a Coast Guard boat and two cutters would remain alongside the boat overnight and that medical personnel would be available for those who suffer sea sickness or other maladies.

"We want to make sure all the passengers are safe," she said.

Divers will try again on Tuesday to untangle the rope.

Maguire said passengers were told they will get refunds and other assistance.

The boat company hasn't returned a phone message seeking comment.