ORIGINAL: Hydro Junkie
For those engines, an aircraft prop of the sizees listed sound about right since I have an OS Max 25FP that says 8X6, 9X5 and 9X6 in the instructions as well. With the RPM ranges listed, I hope you're not planning on putting them into high performance boats as they're both an aircraft engine with a cooling jacket. As far as boat props, I'd start out, depending on the hull, with something around 37mm in diameter for the 21 and a 42mm on the big one
Thanks.
So.
I'm finishing two old-style boats with 31.5 inches long
I think putting the motor 46m on the sport model and 21m in the traditional model
The weight of both without electronics and motor is 1050grs.