The United Way of Southwest Michigan is once again inviting people to sail the St. Joseph River in cardboard boats this week. Thursday will bring the second annual Rock the Boat races at the Inn at Harbor Shores. Just six boats took part in the races last year, and this time around, they’ve got 29. Volunteer teams are tasked with constructing seaworthy cardboard craft using only the base material, duct tape, and polyurethane. They can only be powered by human strength. Those boats will be competing for glory this Thursday starting at 6 p.m. at the Inn at Harbor Shores to raise money for the United Way of Southwest Michigan. Well-wishers are encouraged to stop by to cheer on their favorites.