Welcome,
Props are like a guarded secret with boats. You don't want to let them know what you're running. Were they running stock props or carbon fiber props?

The copper could have been any number of different props. Everyone has their fav though. Some like the x642, or 220, M445, X445, X440/3. There are so many combos with a setup for a boat and the water condition. There are also pros and cons to every prop.
(Here's what I think happened. That one guy figured what everyone else was using and to raise his chances of getting everyone else wet, he used an X440/3. That is if the others had a stock prop.)

I would recommend an x440/3, M445, X642 for starters. But you should really get a few more in your arsenal after reading the below thread. You'll learn a ton about what different props do and don't do. You'll learn what not to do.

http://www.rcuniverse.com/forum/m_4835624/tm.htm

Feel free to ask away using the above link. We'd be more than happy to discuss with you.