What is a good theme for a school project involving boats?

My grade is having groups of 3 people build boats out of cardboard and duct tape. I was hoping someone would have a good idea for a theme but it can’t be:
Titanic, Pirates, or The Little Mermaid.
And it has to be easy to recreate from cardboard, markers, and colored duct tape. I’d really appreciate it!

Niche Profit Sites by