Duxbury selectmen voted unanimously last week to contest the flood-insurance-rate maps drawn up by the Federal Emergency Management Agency. “There were dramatic changes from the old . . . maps,” said Selectman Shawn Dahlen. He said homes on Gurnet Road would be among those particularly affected if the newly designed maps are approved. But, he said, no one knows what the redesign could mean financially. “No one is divulging, from FEMA, what the potential cost is,” he said. “You can’t ask that simple basic question and get an answer.” A public hearing was held recently to allow residents and officials to review and comment on the maps. A presentation was held in early September for Marshfield and Scituate residents. Property owners have until Oct. 17 to appeal their inclusion in the flood zone. “This is not an exact science. There is a lot of subjectivity to some of these decisions,” said Dahlen. He said in some cases assumptions are made about what bridges might be washed out in a 100-year storm, resulting in more flooding than there would be if they hold firm. Selectmen authorized up to $10,000 be spent to hire firms to review the maps.