Fuel advantage of raked propeller

The technology was invented by the Wright brothers. They used a household fan and an oily rag they set on fire. The smoke showed what the air flow was doing. The same method is used in water. Dye markers show what the water flow is doing.
Gilteva: be polite

 

Bravo Gonzo

 

The diameter and "disk area" is huge compared to boat props. A 40hp OB will have a 13.5" dia prop and my 40hp ultralight aircraft had a 57" dia prop. Pushed and acted upon a much greater volume of fluid.

Standing alongside the UL holding on to it at full throttle you know the jobs getting done. There was an UL (tractor) that had a 72" dia prop.

 

The OP obviously needs to do some study. My comments suggested the point. The dynamics are well understood, even though water is clear and air invisible.

 

@ Gilteva:

There are already "raked" propellers for planes. The problem is, that centrifugal forces require a straight blade. If rake is necessary, it can only be done by applying "winglets" on the prop blades.

I have already done a lot of research with CFD. These can show you the airflow and I bet that it will show you that there is inefficiency at any bending in your prop design.

Bendings cause interference drag, which is also the reason for airliners to switch from Winglets to Sharklets (Winglet with elliptic bending instead 90° edge) in order to get the last remaining percent in efficiency.

Best regards, Andreas