Thinking something 3-4 in Dia, five or six blade with a surface piercing profile on the blades. I'm pretty sure nobody makes something like that so it will be custom work. I am going to start out with 3d printing which will probably not be able to handle the loads so then maybe onto aluminum castings or finding someone with a 5 axis mill. I know the size and RPM range is pretty unconventional for an RC boat but I'm not trying go fast, I want to do low cost research. Don't know if it will work or not but that's the business: prototype, fail fast, and iterate or move on.