A direct object always follows an action verb. The first step to determing the direct object is to identify the subject and then the action verb. Then you need to ask yourself "whom" or "what" is receiving the action.
The subject is "the townspeople" and the action verb is "launched." What is being launched? The boat.
Keep in mind that there can be sentences with more than one direct object and some sentences that don't have a direct object.
The president and vice president must be a natural-born citizen of the United States, at least 35 years old, and have been a resident of the United States of America for at least 14 years.
