Propeller
At low speeds size matters. Hence the propeller should have a large diameter. On the downside the duct must also be larger.
I was looking for the largest propellers for RC Boats and ordered the MS-Propeller Serie 146 3Bl-130-R-M5 for 58€.
Mounting: M5
D [mm]: 130,0
Pitch [mm]: 133,2
Max. RPM [U/min]: 2150
Furthermore I ordered the low power boat prop Solas Amita 3 (Solas - Link to source)
Mounting: 10mm
D: 7 1/4"
Pitch: 6"
The hub radius is 49mm → 50mm tube would be perfect
The price of 40€ fits to my goal of keeping the costs down.
Based on these props we get the following motor requirements. RPMmin for 11km/h and RPMmax for 20km/h.
As we see the RPM max for the Raboesch propeller is slightly higher than RPMallowed (2581>2150) based on the propeller specification. It might be possible, that 20km/h would be a little to much. On the other hand the calculation is done with 20% slip, which might be a little to high… maybe RPM would be lower.
Right now I intend to use the Solas Amita3. I could not find suitable foldable props. Please reply if you know any!!! The only ones I found were for yachts and very expensive.