The 229 meter long freighter Petalon loaded with coal went aground in the Thimble Shoals Channel, Chesapeake Bay.   The vessel was refloated a few hours later.   The Coast Guard sent out a navigation team to check to see if the navigation buoys are in the proper place.   The Army Corps of Engineers are also doing a survey of the channel to verify the depths.   The Petalon will have an inspection for damage.   No reports of injuries or pollution being released.