Looking for a fun boat? Take a look at the Springer type tugs. Zipp Kits is one manufacture that makes the Springer easy to build and inexpensive. You can easily scratch build on yourself. I bought four of these.
At 18 inches long they are small and "turn on a dime" and can be quite quirky like trying to ride a wild horse - a lot of fun. You can build them in almost any style (above the deck) from looking like a real truckable pushboat (like this model) to something completely zany. Let you imagination run its course.
If you follow the regulations/specifications, these boats are meant to be "one-design" that is from the deck down there as rules and dimensions that apply so the boats can compete in water sports and racing.
This one is base on a real pushboat that I found on the internet. The cabin can rise up thanks to some old inkjet printer parts I save a while back.