Working Gill Jet (also called Pump Jet or Azimuth Thruster) for RC model boat application. The water duct is about 12 mm in diameter with controllable thrust vector that can be steered by a small RC servo.
Additionally needed parts:
The air vent (pointing up) is used to let out the air when the boat is watered and can either be used as is or shortened and connected to a silicone hose of about 3mm inner diameter. The impeller drive is set up to be used with a 12mm propeller (not included); the impeller part is removable for easier installation but needs to be glued to be waterproof once the propeller is installed (no O-ring seal).
For an assembly manual, details and further background information: see www.microboathobby.com (download section)