The National Transportation Safety Board is planning a Saturday afternoon briefing on the deadly crash of a duck boat and charter bus on a Seattle bridge. The investigation, which is expected to take months, is being watched by other operators of the popular duck boat tours. The amphibious vehicle tours are offered throughout the United States. Four international students died in the crash Thursday after witnesses said the duck boat veered into the oncoming bus. Federal investigators will spend a week or more inspecting the wrecked vehicles and the bridge and interviewing witnesses. Officials say 15 people remain hospitalized at Harborview Medical Center, including one in critical condition. The city of Seattle established a private location for families of the deceased and injured to receive assistance and counseling.