Hi, you have done a couple boats. How about this
build a foam boards for two fishermen. In yhe hull is a panel that if it records a hit the panel pops off and the canoe inks or roll over. Now the senario is c guys nshore hav an rc sub. They surface like the German U boats. Through a recorder they command the fishermen abandon ship. They speak German through interpreter. If the fishermen refuse, the U boat says you will be torpedoed. In some time say 2 minutes. The U boat releases an rc torpedo nd hits the marker on the canoe and water starts pourin in. Canoe rolls overb over. Angered fishermen start yelling at rc guys standing on shore, laughing like crazy.
model torpedoes are pretty hard to make. Possibly power with co2 cartridge, maybe two. Used as jets. Driving props is very difficult even counter rotating. A few guys have done them. There are a few under water videos . Maybe have a camera in the torpedo and do FPV control. It’s important that the torpedo not rotate, so fins must be aligned. Carefully.