Simple subject = boat
The simple subject is the specific subject without any modifiers that describe the subject.
Complete subject = A small boat
The complete subject includes the simple subject and any modifiers. The modifiers describe the subject and are usually adjectives.
Simple predicate = travels
The simple predicate is the main verb. in this case it is an action that tells what the boat is doing.
Complete predicate = travels there every hour.
The complete predicate is the main verb along with any modifiers and other details that describe what is going on.