Higher pitch propellers for trolling motors seems to be a common theme on the internet, but I have not found much in the way of useful information to make decisions per the way forward.
I have a 165 pound semi-planing hull that will run about 10 MPH with a 2.3HP engine, and I would like to maximize the performance with an 86# thrust trolling motor (maybe 8 MPH). Given a 1,152 watt brushed DC motor with an efficiency of ~80%, that is about 1.2 HP. With a slower (1,800 RPM with no load) larger diameter propeller that is more efficient than the ICE counterpart, maybe it is approaching the performance of a 2HP outboard. In any event, the goal is to maximize the speed of the boat with this particular trolling motor, rather than to spend thousands of dollars on an electric outboard.
There are many references to a thin cross-section blade with a large diameter being the most efficient, a key factor for electric boats. However, Torqeedo and Epropulsion have more traditional looking propellers, although again with a larger diameter, so I cannot help to believe that their propellers are superior in some way (more rugged, larger surface area, etc.). I would like to try the Epropulsion Spirit and Navy 3.0 propellers given the lower cost as compared to Torqeedo, a diameter similar to my stock propeller (10.1"), and propeller pitches in the 6" range (about right per the online propeller calculators). However, there is not enough information (shaft diameter, distance from hub face to drive pin, and maximum outside hub diameter) to determine the mounting options in advance of purchasing. If anyone has this information, it would be greatly appreciated, especially the maximum outside hub diameter.
It is common that folks dismiss these electric outboard propellers based on the direction of rotation. I do not believe there is any degradation in the performance of a brushed DC motor with respect to the rotation direction, unlike some other DC motor configurations. My trolling motor wire leads are easily reversed at the speed controller, and the resistor coils are not polarity sensitive. If someone knows differently, please advise.
I also plan to try the RC plane pusher propeller (Masterscrew 15 x 7 as suggested in the Tech Ingredients hydrofoil catamaran), but I do not know what to expect for performance (are the blades strong enough, is there enough surface area, and will the airfoil shape of the blades cavitate at 1,800 RPM?). The good news is that the blades are inexpensive, come in many sizes and pitches, and are easily retrofitted (enlarge the hub hole, construct a backer plate/bushing that accepts the drive pin through the motor shaft, and reduce the diameter to match the rated current maximum of the motor).
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