Childen/young teen series Resembling Percy Jackson, read between 2002-2006

The series had at least 4 books in it. The main character traveled around fighting monsters. In one book he fought Medusa. In another email was being lured to an island by sirens. I believe he fought a cyclops. He traveled by boat. The covers were each a different color if I’m remembering correctly. For some reason I want to say the main characters name was Nick but that might be wrong. That’s about all I can remember.