Here is a concept for a hybrid jet/propeller drive. This concept avoids mechanical gear reduction while allowing a larger propeller for better efficiency.
The motor spins a pump.
The water then flows through a turbine rotating the opposite direction.
The turbine and propeller are a single integrated part
The turbine/propeller will be designed to decrease rotation speed of the turbine and increasing torque; hydraulic gear reduction.
The turbine/propeller will spin freely during unpowered foiling