NAHANT – A U.S. Coast Guard helicopter spotted a small pleasure boat under the waves in Lynn Harbor late Thursday morning, according to Nahant Harbormaster Robert Tibbo.He said the vessel was moored off the state Department of Conservation and Recreation boat ramp _ which is located on the border of Nahant and Lynn _ and apparently sank sometime Wednesday during the winter storm that hit the area.Tibbo said he called in a Coast Guard helicopter to fly over the area late Thursday morning to help locate the boat.?The U.S. Coast Guard determined the boat sank at its mooring,” Tibbo said.No one was on the boat when it sank, he said.Read Friday’s Daily Item for complete coverage of the story.